“Hi Ship, I have a quick question for you regarding repairing cables....
I was always taught that if you damage or if it gets cut in half, that you basically stick a new plug on each end and give yourself 2 cables. In some instances this is quite acceptable but not always.
My problem is that repairing even a simple 3 core power cable causes the repaired area to be rigid and thus susceptible to breaks on either side of the join.
I was taught to stagger the joins on a multi core cable (where the individual cores are insulated) to ensure that you don’t end up with a bulge, and to limit shorts.
Eg:
Core 1 --------xxxxx-----------------------------
Core 2 -------------------xxxxx------------------
Core 3 ------------------------------xxxxx-------
Where xxxxx indicates a join.
Each join is soldered (keeping the join to about 6mm), covered with heat shrink and the exposed cores are then wrapped with electrical tape to make up the missing outer insulating cover. The whole area is then covered with a length of heat shrink.
This works perfectly for installations but I am not all that happy with the results for most other applications as the cable is continuously rolled and unrolled etc. “
This is my method:
What you describe is a rolling or offset line splice. This is a NEC approved method for line splicing but only when done properly and you are not. First heat shrink is not a approved method of replacing the insulation over the conductors for four reasons. First it in it’s normal type, it is not water proof, second with age and flexing it can tear, re-expand and move, third unless your solder joint is completely smooth, it can develop tears or punctures in it, and forth the largest reason is any protections you do to the wire must provide at least an equivalent if not 1.½ times the amount of insulation around the conductor per what was there before the splice. In addition to that, should there be a heating of the wire by way of too much amperage or voltage drop or the solder is a cold solder joint, the heat induced at the splice can be enough it will either melt the solder and allow the wires to become separated, or burn thru/cut or what ever the heat shrink. That’s just the heat shrink, electrical tape is not recognized as a permanent insulation replacement, nor will most of it hold up to your purpose without creeping, peeling etc. than it also will not be water tight. Electrical tape, especially typical store bought electrical tape has problems with heat, humidity and cold, and even if it were wrapped around the repair in sufficient thickness to reproduce the insulation covering the conductors, it still most likely will not be permanent, flexible, water resistant or adhere to the cable jacket strongly enough.
The method of splicing cable including rolling splices is primarily used for power supplies to outhouse, sheds and barns when buried or supported, otherwise not an approved or normal way to join cables for power. Such cables would not be subject to flexing, coiling and other abuses that your power cords would be. When such permanent install splices are done also they follow a specific set or rules for how to do so and how to replace the insulation between conductors. Soldering the joint while still acceptable has for the most part also been replaced by other splicing methods which are easier and stronger.
Your method would be fine for splicing multi-channel/pair data cable or sound snakes if expensive enough to try and save at the length, but for live power I would avoid this method and remove any such repairs from the inventory. On the whole, the rule of thumb for my application is there is no splices in live power cords without UL listed connectors and plugs between two sections of it. Simple rule which prevents guess work or possibly unsafe conditions.
Cable is cheap enough that if becomes damaged or broken, just replace it. If you cannot afford to replace what is not safe to be repairing, you should not be using it. Even on multi-circuit Socopex cable, if there is a cut in a conductor’s insulation, cut the cable there it’s part of the price of being in the business. You do not compromise safety. Ever. We all know this but have our own ideas of what is safe often based upon a lock of knowledge about it. By my standards, even if there is only a cut in the jacket and the insulation on a conductor exposes bare wire, cut it. Broken/cut strands even if for the most part the conductor is in tact means resistance at that point thus heat. This is what causes airplane crashes as I watched last night 12/17/04 on NOVA - a PBS show. Basically with heat the insulation in some planes develops cracks. With water, they arc together and cause a fire that brings down planes. Same concept with our cable, unless absolutely water tight but still flexible enough, even repaired cable can arc from just a little crack. Data cable does not have enough voltage to arc between conductors for all intensive purposes, the worst that will happen is you loose a control cable. With that repairs can be done but frequently are smarter to just cut also because they have the nasty habit of re-breaking or shorting later. Basically, if there is conductors/bare copper exposed on power cord, cut it.
CABLE JACKET REPAIR:
If you are repairing a cut in the cord and after inspection of the conductors, there is no exposed wire, it is safe to repair the outer jacket as long as no more than 50% of the circumference of the cable has been compromised. The reason for this is as the cable is stretched, unless at least 50% of the neoprene or thermoplastic is still linking the two sections together, it very likely will tear free of any repair re-exposing the inner conductors and adding stress to them. Also if the cut runs the length of the cable by more than 12"(300mm) as an absolute maximum, it is not worth repairing.
In addition to these dimensions, cable showing signs of age such as dry rot or other age, temperature, chemical or other abuse related damage such as crushing or extreme bending as a whole to the cable should not be repaired.
First if the writing either imprinted into it or written on it’s side is no longer observable along the majority of it’s length it no longer is Code Compliant for use, you need to be able to read what the cable is gauge/conductor/voltage wise plus the manufacturer. Second if you flex it and it shows little cracks all over the jacket which are more than just minor and surface level, the cable’s jacket has been compromised and should not be used. It is no longer water tight, dielectrically safe, or offering physical protection sufficient to protect the conductors - it’s gonna break again. Remember, this is power cord, it has a service life, don’t push it past that because if the outer jacket shows especially rot, the inner conductors will very likely have just as much damage and often be oxidized - air and moisture making it higher resistance. If the writing has warn off, especially if the neoprene becomes about slick and shiny in appearance instead of matt finish, it’s often about on it’s last legs for age and use and most of the time it’s inner conductors will be oxidized also.
I use three main methods for cable repair that are based off the line splicing techniques in Division 2 of American Electrician’s Handbook 13th Edition by Croft/Summers.
XLR/DMX Cable Repair: Not worth much, repairs to it’s jacket will be less electrically permanent repair and more or a permanent nuisance repair to it. First if the cable has any glue remaining from tape once covering it, the remaining adhesive needs to be completely removed by Goof Off or Goo Gone. Avoid abrasives on the cable jacket such as censers, steel wool or sand paper, it will not do a proper job of removing the adhesive and might damage the cable’s ability to accept glue. If the adhesive, paint or what ever is on well enough Goof Off will not take it off, leave it in place. Next the cable will be cleaned to remove the Goof Off and any dirt with Naphtha. Adhesive does not stick to dirt, oil, much less Goof Off a adhesive remover, your cable must be clean. Next apply a light layer of rubber adhesive to the surface extending beyond the cut by at least an inch.
There are three types of adhesive that are acceptable. First is rubber cement such as bicycle tire repair cement. This will work on neoprene/rubber insulated jackets but not thermoset or thermoplastic jackets as well. You must let the cement dry before you apply anything to it or it very likely will melt thru what you apply to the adhesive. Rubber/butyl/neoprene adhesive as opposed to rubber cement otherwise works well depending upon brand and type as long as it is allowed to set up. It will also work slightly better on the plastic types of wire. Some trial and error is necessary, as with a method of application of thin even coatings. The best adhesive for general purpose cable work on all types is 3M #2141 Rubber/Neoprene Adheasive. The smallest quantities available for it is in 1 Quart cans, and because it is fast drying, use of a glue pot or other specially designed applicator is necessary for more than one time use from the remaining quart. In other words, put it in a glue bottle, open the can than re-seal it, or any other method normal to glue application will expose the adhesive to the air and it will set up. Once the adhesive thickens, it is not possible to thin it and often will not be as strong in adhesion.
Glue pots are specially designed containers with a brush as part of it’s self sealing lid. Such items are not too expensive but hard to clean as will be necessary between fillings, short of taking the glue pot apart and re-sealing it with silicone each time. Brushes are easy to get and inexpensive.
This is a very good general purpose adhesive for most flexible plastic or rubber like things especially cable, but unless you have constant use for it the glue will get expensive due to even in a glue pot, it has a limited shelf life of 6 months on the outside once opened. It also needs to be well mixed for the initial use, having a paint company mix it for you on a machine will be helpful. #2141 runs about $20.00 per quart thru McMaster Carr #7509a74 so it’s not very cheap - you do not want to waste it.
Setup time is in the range of 30 seconds for a thin layer, to two or three minutes for a thicker layer this includes the brush so you need to apply the glue and don’t linger, stick the brush back into the glue pot as soon as possible this will both prevent the brush from drying and becoming gummy, and help prevent the remainder of the pot from drying too fast. The major advantages of the glue is it’s setup time and superior adhesive qualities. This is a very good glue, however if in a school you might want to verify with the MSDS data sheets such chemicals are allowed to be used or in stock. It is flammable but safe enough in use with a heat gun. A final advantage of using this adhesive is that once it’s dry it, any glue not under the tape will be safe to touch and leave exposed because it is no longer sticky. You want the adhesive to extend past the tape, the alternative option is having parts of your tape not permanently bonded to the wire since it is not atop the adhesive.
Since this is data cable, it is not worth a major repair job to it. In addition to that, if your repair using normal methods expands the size of the outer jacket too much, it will be a snag point for the wire as it is pulled and be subject to more abuse than the repair can withstand. Also, the dia. of the wire is too small to properly apply other forms of covering to it other than heat shrink below.
For these reasons, especially cost effectiveness verses labor, I use electrical tape atop the adhesive. If you are making a repair with electrical tape, use the best tape you can so it does not come loose. This stuff is abused and exposed to handling not sealed up within a wall box. It’s temperature and moisture exposures will be subject to more extremes than household electrical tape will be exposed to also. In other words, use 3M Super 33, there is no better general purpose electrical tape on the market for cable repair. Otherwise if the cable is to be exposed to extreme cold, use cold weather electrical tape. The Super 33 will for the most part stick well to itself but not sufficiently to the cable jacket thus the adhesive is necessary. Two to three stretched and tapered layers is sufficient in most cases as protection over the cut.
Atop the electrical tape I apply Black Liquid Electrical tape. Frequently I will apply it directly to the electrical tape or add another layer of adhesive than the Liquid E-Tape. This takes the place of cable paint as required for splicing, but since cable paint is not generally available on the market, the Liquid E-Tape when fresh will suffice. Liquid E-Tape is available in 4oz containers with a brush on it’s lid, when it becomes a little less fresh it will not paint the cable very well but will fill holes better - see below. Again it has a shelf life, you need to ensure the cap goes all the way back on after use and don’t expect it to last once opened more than a few months. The purpose of the Liquid E-Tape is three fold. First it provides added water resistance to the tape and repair. Second it adds to the abrasion resistance of the tape and will help prevent it from coming loose or rolling up along it’s edges. Third it provides a visible indication that the repair has been inspected and properly repaired as opposed to a repair with just electrical tape covering it but no idea if it was properly repaired and inspected. If the cable is subject to a lot of abuse, it might be necessary to periodically re-apply the Liquid E-Tape.
If the cable does not have a connector on it, often it will be easier to install some heat shrink with the above adhesive over the cut, or to slightly stretch a 3/4" expanded 3:1 or 4:1 heat shrink so it fits over the plug so it will shrink down over the cut. Expanded 3/4" heat shrink at 3:1 shrink ratio will shrink down to about 1/4" dia.
Power Cable Repair with it’s ends off: If the cable does not have a plug on it, or it’s easy enough to remove it, heat shrink with adhesive under it as per the above method will work sufficiently to protect a cut but not a hole in the jacket. In this case you will want to apply some Liquid E-Tape into the cut to adhere it together and seal the cut. Liquid E-Tape inside of cut has the advantage over adhesive of not being as strong of a bond which if it also adheres to the inner conductors can make the insulation over them tear off and expose conductors inside the jacket as the wire moves. It is necessary to ensure inner conductors are allowed to remain independent from the outer jacket because within the cable jacket they will have different amounts of movement from the outer jacket. I tend to use red Liquid E-Tape to seal up a cut, this way should the cut become exposed again it is much easier to spot the needed repair. Liquid E-Tape does not stick that well to thermoplastic insulations such as on most Socopex type or SJT/SJE cable but will fill the hole in preventing the opening from constantly opening and closing. An alternative would be to use the adhesive as long as it does not glue inner conductors to the repair. Again, if the inner conductors are also cut you are better off not attempting to repair the cable.
As per the above XLR repair, clean the cable jacket with Goof Off as needed than Naptha, than apply some adhesive and allow it to set up. In this case, you want to extend past the cut at least four times the diameter of the cut for proper protection of the repair. A light even coating of adhesive is better than a thick one that can become hard and crack, or even bubble up. An added advantage of the adhesive will be that as opposed to normal heat shrink that splits when over heated, the adhesive below the heat shrink once it is compressed enough will bond to the glue and not split. Above the adhesive apply sufficient layers of heat shrink to bring the repair up to the same thickness as the cable jacket started out to be. In other words, for a SJ type cable that’s two layers of ½" expanded 2:1 Polyolefin heat shrink, or possibly one of a 3/4" expanded 2:1 or 3:1 heat shrink due to it’s completed shrunk thickness. On XLR cable, as single layer is probably sufficient, but on SO and SC grades of cable, multiple layers might be necessary. It might be advisable to apply some adhesive between layers of heat shrink to prevent it from re-expanding. Avoid PVC heat shrink, it is not UV resistant and in general does not flex well or last as long. A single layer of adhesive lined 3/4" expanded 3:1 heat shrink will work best for all cuts including ones with slight holes. Basically it is heat shrink with hot melt glue inside of it which will allow it to stick to other layers of heat shrink or repairs better. Note the hot melt glue is insufficient to bond with the neoprene jacket, rubber adhesive is still necessary, but it in addition to the hot melt glue will produce a very good bond, and a tough hard repair which is very abrasion and damage resistant. It’s disadvantage is it will not be flexible so it’s maximum serviceable length for a repair is 6". Shrink tubing in general should not be used for repairs of over 8". Once the heat shrink is on no further covering should be necessary.
Of note on heat shrink is you need to slide it into place before the adhesive has set up or you might not be able to slide it into position. Should your adhesive set up before the heat shrink gets into place, Denatured Alcohol will often temporarily allow the heat shrink to slide. Once the heat shrink is in place, allow the glue to set up before shrinking it or it might boil and create a bubble in the heat shrink. Should a bubble develop, do not puncture it, let it shrink down on it’s own. Or replace the heat shrink if it does not go away. Take that part of the heat shrink away from the heat as soon as possible, allow the heat shrink to cool and hopefully bubble go down, than continue shrinking it over the repair.
Vulcanized Power Cord repairs in General: This method will work very safely when used for anything from 4/0 feeder cable to fixture whips - though fixture whips are better off with heat shrink repairs if not replaced overall. It is directly based upon the above book’s intent, only the length of the splice and thickness has been reduced due to flexibility needs and the fact that the inner conductors still have their factory protection over the conductors. You are not covering a splice, just fixing a cut or hole in the outer jacket.
Step one: clean the cable as above than fill the hole with Liquid E-Tape. Allow it to set up if not come very close to drying if it is used to fill in a hole up to ½" in dia. If the hole is large and long or larger than ½" it will be necessary to use friction tape as long as the jacket of the cable is not compromised by more than 12" or ½ it’s circumference. If it is necessary to apply a thick layer of Liquid E-Tape, it is necessary to let is set up if not come very close to drying, adhesive will bond with it but will loose some of it’s strength in bonding tape to cable jacket if mixed with Liquid E-Tape and smeared on the cable jacket. This repair technique assumes 3M #2141 adhesive is used in general other than where other notes are involved for rubber cement such as rubber cement does not bond as well with Liquid E-Tape so it’s use is limited on friction tape repairs.
Apply adhesive to the cable jacket and Liquid E-Tape. If your hole is large or a wire is popping out of the jacket, it will be necessary to apply friction tape over the hole or around the cable in pushing the wire into the hole. In the case of a hole, it will replace the strength of the jacket with a strong covering protection over it. Three layers thick of friction tape for a minimum over wires and holes. If you are covering a long or wide cut, friction tape in general can be of value in pulling back together the cable jacket and offering a strong protection to it. In the case of a wire that has pulled out of the jacket, it’s a value question as to if it is better to cut the cable at that point or attempt to fold the wire back into the cut, hope it pulls back into the cable or at least letting the friction tape protect it. On normal power cord, cutting the jacket will be the best option. For Multi-Cable with a thermoplastic jacket, likely the thermoplastic covering will not be overly adversely bonded to the Liquid E-Tape or Friction tape and the conductor will move some as normal, but not pull itself back into place if it is out any real distance from the jacket. Be careful not to apply any adhesive directly to this wire or any wires in general under the friction tape. Liquid E-Tape protected wires can have adhesive attached to it, but otherwise it is better to let the friction tape attach directly to the conductors as it will not rip off their insulation. The friction tape will be strong enough to hold the wire in it’s place and prevent the jacket from bunching up or spreading apart. Next apply a generous amount of adhesive over the friction tape. This will serve a double purpose. First it will allow the rubber splicing tape to bond with the friction tape, and second it will act as a somewhat flexible hardener for the friction tape in much the same way as application of rosin or epoxy on fiberglass sheets works.
If you are not repairing a large hole or cut, friction tape is not necessary skip it’s step and start with Liquid E-Tape in the cut, than apply and let set up the adhesive to the jacket. The adhesive should extend at least 2" past the end of the cut, and up to 4" depending upon the cable thickness and amperage. Next apply self-vulcanizing rubber electrical splicing tape to the adhesive. If you are using rubber cement, you will need to wait for the cement to completely dry or it will burn thru rubber splicing tape and reopen the hole no matter how many layers of tape you put on it. Otherwise with adhesive you need to allow it to set up because if still wet it likely will not complete drying and might not allow the tape to adhere sufficiently or tight enough. Rubberized electrical tape will permanently bond to itself but not the cable jacket thus the need for adhesive. It will provide a water tight, and electrically intact and safe protection over the repair in sufficient thickness as required. This needs to be as thick as the cable jacket and extend for at least thee times the diameter of the cable past the cut. Normally this would mean three stretched and tapering layers over a SJ cable or more on a SO or SC cable. You stretch the tape until it either changes colors or becomes half width, and if it has a plastic tape covering over the rubber splicing tape, you do have to remove the plastic as you apply the tape. Also if you do not stretch the tape sufficiently, it will not vulcanize to itself, and will probably fall apart with time. Start at the cut and work off to one direction, than back towards the center and to the other side. Continue wrapping the cut in a tapered pattern meaning the second layer will end ½" in from the layer below it. This will allow for the cable to be pulled without snagging or flex easier. You are looking for a rounded or smooth repair. Should the tape break as you stretch it, apply the next section, start wrapping the tape again near where it broke, wrap the tape back on itself to cover the end and starting seams than continue on. The goal in rubberized electrical tape as with any taped repairs is to only have one seam - the end of the tape where it is cut exposed, where you start wrapping and where it breaks should be covered by the tape completely. After you cut the tape, stretch and push to blend the end of it into the repair so the seam well adhered and not as easy to snag. Three layers of Rubberized Electrical tape would be about the norm for SJ cable.
Apply a layer of adhesive above the rubberized electrical tape and allow it to set up. Extend the glue 1" past the rubberized electrical tape. Apply two layers of Super 33 tape atop the glue and extend it 3/4" past the edges of the rubber E-Tape. The Super 33 will provide abrasion resistance to the otherwise too soft rubber electrical tape. If you attempt to apply more than two layers of Super 33, there is an increased chance it will with use loose it’s bond with itself and become unraveled. Stretch the Super 33 by about 1/3 it’s width. Apply a thick layer or two normal coatings of Liquid E-Tape over the electrical tape. Wait for the first layer to dry before applying a second coating of Liquid E-Tape. This will complete the repair and provide extra weather and abrasion resistance. For added abrasion resistance, you can apply a very light layer of adhesive atop the Super 33. Allow it to set up and almost dry before adding the Liquid E-Tape, this will better bond the Liquid E-Tape to the repair. With use it might be necessary to apply more Liquid E-Tape over the repair or use cable paint such as a electrician/linesmen might use if you can find any.
These are the methods I have developed and have been using for cable repair for about 5 years now professionally. They work very well to protect the cable and are permanent. If done properly with a taper, the repair will not be overly large or too seriously effect it’s flexibility.
Never trust anything that is just taped together as a repair. This is a temporary repair at best and possibly covering something that can be dangerous. All it takes is a little moisture, heat or exposed conductors and your wire given sufficient amperage and voltage can short causing all kinds of problems if not a fire. Proper repairs are very necessary if you want to continue using the cable without cutting it and making it into at best two usable sections. If not the above or an even more proper linesmen’s splicing covering method, just cut the cable and make what ever you can out of it. Electrical tape alone does not make a permanent repair, it just makes me suspicious. All repairs need to be inspected by trained personal looking for damage to the conductors before it should be repaired permanently than placed back into general use stock. Should you need to do an in the field repair to cable, it is a nice courtesy to provide a strip of colored electrical tape near the repair in a yellow orange or red so such a repair will be noticed after the production. An alternative method especially for feeder cable would be to apply the friction tape and rubber tape as above, than use heat shrink to form the outer protective skin over the repair.
Brian Shipinski
I was always taught that if you damage or if it gets cut in half, that you basically stick a new plug on each end and give yourself 2 cables. In some instances this is quite acceptable but not always.
My problem is that repairing even a simple 3 core power cable causes the repaired area to be rigid and thus susceptible to breaks on either side of the join.
I was taught to stagger the joins on a multi core cable (where the individual cores are insulated) to ensure that you don’t end up with a bulge, and to limit shorts.
Eg:
Core 1 --------xxxxx-----------------------------
Core 2 -------------------xxxxx------------------
Core 3 ------------------------------xxxxx-------
Where xxxxx indicates a join.
Each join is soldered (keeping the join to about 6mm), covered with heat shrink and the exposed cores are then wrapped with electrical tape to make up the missing outer insulating cover. The whole area is then covered with a length of heat shrink.
This works perfectly for installations but I am not all that happy with the results for most other applications as the cable is continuously rolled and unrolled etc. “
This is my method:
What you describe is a rolling or offset line splice. This is a NEC approved method for line splicing but only when done properly and you are not. First heat shrink is not a approved method of replacing the insulation over the conductors for four reasons. First it in it’s normal type, it is not water proof, second with age and flexing it can tear, re-expand and move, third unless your solder joint is completely smooth, it can develop tears or punctures in it, and forth the largest reason is any protections you do to the wire must provide at least an equivalent if not 1.½ times the amount of insulation around the conductor per what was there before the splice. In addition to that, should there be a heating of the wire by way of too much amperage or voltage drop or the solder is a cold solder joint, the heat induced at the splice can be enough it will either melt the solder and allow the wires to become separated, or burn thru/cut or what ever the heat shrink. That’s just the heat shrink, electrical tape is not recognized as a permanent insulation replacement, nor will most of it hold up to your purpose without creeping, peeling etc. than it also will not be water tight. Electrical tape, especially typical store bought electrical tape has problems with heat, humidity and cold, and even if it were wrapped around the repair in sufficient thickness to reproduce the insulation covering the conductors, it still most likely will not be permanent, flexible, water resistant or adhere to the cable jacket strongly enough.
The method of splicing cable including rolling splices is primarily used for power supplies to outhouse, sheds and barns when buried or supported, otherwise not an approved or normal way to join cables for power. Such cables would not be subject to flexing, coiling and other abuses that your power cords would be. When such permanent install splices are done also they follow a specific set or rules for how to do so and how to replace the insulation between conductors. Soldering the joint while still acceptable has for the most part also been replaced by other splicing methods which are easier and stronger.
Your method would be fine for splicing multi-channel/pair data cable or sound snakes if expensive enough to try and save at the length, but for live power I would avoid this method and remove any such repairs from the inventory. On the whole, the rule of thumb for my application is there is no splices in live power cords without UL listed connectors and plugs between two sections of it. Simple rule which prevents guess work or possibly unsafe conditions.
Cable is cheap enough that if becomes damaged or broken, just replace it. If you cannot afford to replace what is not safe to be repairing, you should not be using it. Even on multi-circuit Socopex cable, if there is a cut in a conductor’s insulation, cut the cable there it’s part of the price of being in the business. You do not compromise safety. Ever. We all know this but have our own ideas of what is safe often based upon a lock of knowledge about it. By my standards, even if there is only a cut in the jacket and the insulation on a conductor exposes bare wire, cut it. Broken/cut strands even if for the most part the conductor is in tact means resistance at that point thus heat. This is what causes airplane crashes as I watched last night 12/17/04 on NOVA - a PBS show. Basically with heat the insulation in some planes develops cracks. With water, they arc together and cause a fire that brings down planes. Same concept with our cable, unless absolutely water tight but still flexible enough, even repaired cable can arc from just a little crack. Data cable does not have enough voltage to arc between conductors for all intensive purposes, the worst that will happen is you loose a control cable. With that repairs can be done but frequently are smarter to just cut also because they have the nasty habit of re-breaking or shorting later. Basically, if there is conductors/bare copper exposed on power cord, cut it.
CABLE JACKET REPAIR:
If you are repairing a cut in the cord and after inspection of the conductors, there is no exposed wire, it is safe to repair the outer jacket as long as no more than 50% of the circumference of the cable has been compromised. The reason for this is as the cable is stretched, unless at least 50% of the neoprene or thermoplastic is still linking the two sections together, it very likely will tear free of any repair re-exposing the inner conductors and adding stress to them. Also if the cut runs the length of the cable by more than 12"(300mm) as an absolute maximum, it is not worth repairing.
In addition to these dimensions, cable showing signs of age such as dry rot or other age, temperature, chemical or other abuse related damage such as crushing or extreme bending as a whole to the cable should not be repaired.
First if the writing either imprinted into it or written on it’s side is no longer observable along the majority of it’s length it no longer is Code Compliant for use, you need to be able to read what the cable is gauge/conductor/voltage wise plus the manufacturer. Second if you flex it and it shows little cracks all over the jacket which are more than just minor and surface level, the cable’s jacket has been compromised and should not be used. It is no longer water tight, dielectrically safe, or offering physical protection sufficient to protect the conductors - it’s gonna break again. Remember, this is power cord, it has a service life, don’t push it past that because if the outer jacket shows especially rot, the inner conductors will very likely have just as much damage and often be oxidized - air and moisture making it higher resistance. If the writing has warn off, especially if the neoprene becomes about slick and shiny in appearance instead of matt finish, it’s often about on it’s last legs for age and use and most of the time it’s inner conductors will be oxidized also.
I use three main methods for cable repair that are based off the line splicing techniques in Division 2 of American Electrician’s Handbook 13th Edition by Croft/Summers.
XLR/DMX Cable Repair: Not worth much, repairs to it’s jacket will be less electrically permanent repair and more or a permanent nuisance repair to it. First if the cable has any glue remaining from tape once covering it, the remaining adhesive needs to be completely removed by Goof Off or Goo Gone. Avoid abrasives on the cable jacket such as censers, steel wool or sand paper, it will not do a proper job of removing the adhesive and might damage the cable’s ability to accept glue. If the adhesive, paint or what ever is on well enough Goof Off will not take it off, leave it in place. Next the cable will be cleaned to remove the Goof Off and any dirt with Naphtha. Adhesive does not stick to dirt, oil, much less Goof Off a adhesive remover, your cable must be clean. Next apply a light layer of rubber adhesive to the surface extending beyond the cut by at least an inch.
There are three types of adhesive that are acceptable. First is rubber cement such as bicycle tire repair cement. This will work on neoprene/rubber insulated jackets but not thermoset or thermoplastic jackets as well. You must let the cement dry before you apply anything to it or it very likely will melt thru what you apply to the adhesive. Rubber/butyl/neoprene adhesive as opposed to rubber cement otherwise works well depending upon brand and type as long as it is allowed to set up. It will also work slightly better on the plastic types of wire. Some trial and error is necessary, as with a method of application of thin even coatings. The best adhesive for general purpose cable work on all types is 3M #2141 Rubber/Neoprene Adheasive. The smallest quantities available for it is in 1 Quart cans, and because it is fast drying, use of a glue pot or other specially designed applicator is necessary for more than one time use from the remaining quart. In other words, put it in a glue bottle, open the can than re-seal it, or any other method normal to glue application will expose the adhesive to the air and it will set up. Once the adhesive thickens, it is not possible to thin it and often will not be as strong in adhesion.
Glue pots are specially designed containers with a brush as part of it’s self sealing lid. Such items are not too expensive but hard to clean as will be necessary between fillings, short of taking the glue pot apart and re-sealing it with silicone each time. Brushes are easy to get and inexpensive.
This is a very good general purpose adhesive for most flexible plastic or rubber like things especially cable, but unless you have constant use for it the glue will get expensive due to even in a glue pot, it has a limited shelf life of 6 months on the outside once opened. It also needs to be well mixed for the initial use, having a paint company mix it for you on a machine will be helpful. #2141 runs about $20.00 per quart thru McMaster Carr #7509a74 so it’s not very cheap - you do not want to waste it.
Setup time is in the range of 30 seconds for a thin layer, to two or three minutes for a thicker layer this includes the brush so you need to apply the glue and don’t linger, stick the brush back into the glue pot as soon as possible this will both prevent the brush from drying and becoming gummy, and help prevent the remainder of the pot from drying too fast. The major advantages of the glue is it’s setup time and superior adhesive qualities. This is a very good glue, however if in a school you might want to verify with the MSDS data sheets such chemicals are allowed to be used or in stock. It is flammable but safe enough in use with a heat gun. A final advantage of using this adhesive is that once it’s dry it, any glue not under the tape will be safe to touch and leave exposed because it is no longer sticky. You want the adhesive to extend past the tape, the alternative option is having parts of your tape not permanently bonded to the wire since it is not atop the adhesive.
Since this is data cable, it is not worth a major repair job to it. In addition to that, if your repair using normal methods expands the size of the outer jacket too much, it will be a snag point for the wire as it is pulled and be subject to more abuse than the repair can withstand. Also, the dia. of the wire is too small to properly apply other forms of covering to it other than heat shrink below.
For these reasons, especially cost effectiveness verses labor, I use electrical tape atop the adhesive. If you are making a repair with electrical tape, use the best tape you can so it does not come loose. This stuff is abused and exposed to handling not sealed up within a wall box. It’s temperature and moisture exposures will be subject to more extremes than household electrical tape will be exposed to also. In other words, use 3M Super 33, there is no better general purpose electrical tape on the market for cable repair. Otherwise if the cable is to be exposed to extreme cold, use cold weather electrical tape. The Super 33 will for the most part stick well to itself but not sufficiently to the cable jacket thus the adhesive is necessary. Two to three stretched and tapered layers is sufficient in most cases as protection over the cut.
Atop the electrical tape I apply Black Liquid Electrical tape. Frequently I will apply it directly to the electrical tape or add another layer of adhesive than the Liquid E-Tape. This takes the place of cable paint as required for splicing, but since cable paint is not generally available on the market, the Liquid E-Tape when fresh will suffice. Liquid E-Tape is available in 4oz containers with a brush on it’s lid, when it becomes a little less fresh it will not paint the cable very well but will fill holes better - see below. Again it has a shelf life, you need to ensure the cap goes all the way back on after use and don’t expect it to last once opened more than a few months. The purpose of the Liquid E-Tape is three fold. First it provides added water resistance to the tape and repair. Second it adds to the abrasion resistance of the tape and will help prevent it from coming loose or rolling up along it’s edges. Third it provides a visible indication that the repair has been inspected and properly repaired as opposed to a repair with just electrical tape covering it but no idea if it was properly repaired and inspected. If the cable is subject to a lot of abuse, it might be necessary to periodically re-apply the Liquid E-Tape.
If the cable does not have a connector on it, often it will be easier to install some heat shrink with the above adhesive over the cut, or to slightly stretch a 3/4" expanded 3:1 or 4:1 heat shrink so it fits over the plug so it will shrink down over the cut. Expanded 3/4" heat shrink at 3:1 shrink ratio will shrink down to about 1/4" dia.
Power Cable Repair with it’s ends off: If the cable does not have a plug on it, or it’s easy enough to remove it, heat shrink with adhesive under it as per the above method will work sufficiently to protect a cut but not a hole in the jacket. In this case you will want to apply some Liquid E-Tape into the cut to adhere it together and seal the cut. Liquid E-Tape inside of cut has the advantage over adhesive of not being as strong of a bond which if it also adheres to the inner conductors can make the insulation over them tear off and expose conductors inside the jacket as the wire moves. It is necessary to ensure inner conductors are allowed to remain independent from the outer jacket because within the cable jacket they will have different amounts of movement from the outer jacket. I tend to use red Liquid E-Tape to seal up a cut, this way should the cut become exposed again it is much easier to spot the needed repair. Liquid E-Tape does not stick that well to thermoplastic insulations such as on most Socopex type or SJT/SJE cable but will fill the hole in preventing the opening from constantly opening and closing. An alternative would be to use the adhesive as long as it does not glue inner conductors to the repair. Again, if the inner conductors are also cut you are better off not attempting to repair the cable.
As per the above XLR repair, clean the cable jacket with Goof Off as needed than Naptha, than apply some adhesive and allow it to set up. In this case, you want to extend past the cut at least four times the diameter of the cut for proper protection of the repair. A light even coating of adhesive is better than a thick one that can become hard and crack, or even bubble up. An added advantage of the adhesive will be that as opposed to normal heat shrink that splits when over heated, the adhesive below the heat shrink once it is compressed enough will bond to the glue and not split. Above the adhesive apply sufficient layers of heat shrink to bring the repair up to the same thickness as the cable jacket started out to be. In other words, for a SJ type cable that’s two layers of ½" expanded 2:1 Polyolefin heat shrink, or possibly one of a 3/4" expanded 2:1 or 3:1 heat shrink due to it’s completed shrunk thickness. On XLR cable, as single layer is probably sufficient, but on SO and SC grades of cable, multiple layers might be necessary. It might be advisable to apply some adhesive between layers of heat shrink to prevent it from re-expanding. Avoid PVC heat shrink, it is not UV resistant and in general does not flex well or last as long. A single layer of adhesive lined 3/4" expanded 3:1 heat shrink will work best for all cuts including ones with slight holes. Basically it is heat shrink with hot melt glue inside of it which will allow it to stick to other layers of heat shrink or repairs better. Note the hot melt glue is insufficient to bond with the neoprene jacket, rubber adhesive is still necessary, but it in addition to the hot melt glue will produce a very good bond, and a tough hard repair which is very abrasion and damage resistant. It’s disadvantage is it will not be flexible so it’s maximum serviceable length for a repair is 6". Shrink tubing in general should not be used for repairs of over 8". Once the heat shrink is on no further covering should be necessary.
Of note on heat shrink is you need to slide it into place before the adhesive has set up or you might not be able to slide it into position. Should your adhesive set up before the heat shrink gets into place, Denatured Alcohol will often temporarily allow the heat shrink to slide. Once the heat shrink is in place, allow the glue to set up before shrinking it or it might boil and create a bubble in the heat shrink. Should a bubble develop, do not puncture it, let it shrink down on it’s own. Or replace the heat shrink if it does not go away. Take that part of the heat shrink away from the heat as soon as possible, allow the heat shrink to cool and hopefully bubble go down, than continue shrinking it over the repair.
Vulcanized Power Cord repairs in General: This method will work very safely when used for anything from 4/0 feeder cable to fixture whips - though fixture whips are better off with heat shrink repairs if not replaced overall. It is directly based upon the above book’s intent, only the length of the splice and thickness has been reduced due to flexibility needs and the fact that the inner conductors still have their factory protection over the conductors. You are not covering a splice, just fixing a cut or hole in the outer jacket.
Step one: clean the cable as above than fill the hole with Liquid E-Tape. Allow it to set up if not come very close to drying if it is used to fill in a hole up to ½" in dia. If the hole is large and long or larger than ½" it will be necessary to use friction tape as long as the jacket of the cable is not compromised by more than 12" or ½ it’s circumference. If it is necessary to apply a thick layer of Liquid E-Tape, it is necessary to let is set up if not come very close to drying, adhesive will bond with it but will loose some of it’s strength in bonding tape to cable jacket if mixed with Liquid E-Tape and smeared on the cable jacket. This repair technique assumes 3M #2141 adhesive is used in general other than where other notes are involved for rubber cement such as rubber cement does not bond as well with Liquid E-Tape so it’s use is limited on friction tape repairs.
Apply adhesive to the cable jacket and Liquid E-Tape. If your hole is large or a wire is popping out of the jacket, it will be necessary to apply friction tape over the hole or around the cable in pushing the wire into the hole. In the case of a hole, it will replace the strength of the jacket with a strong covering protection over it. Three layers thick of friction tape for a minimum over wires and holes. If you are covering a long or wide cut, friction tape in general can be of value in pulling back together the cable jacket and offering a strong protection to it. In the case of a wire that has pulled out of the jacket, it’s a value question as to if it is better to cut the cable at that point or attempt to fold the wire back into the cut, hope it pulls back into the cable or at least letting the friction tape protect it. On normal power cord, cutting the jacket will be the best option. For Multi-Cable with a thermoplastic jacket, likely the thermoplastic covering will not be overly adversely bonded to the Liquid E-Tape or Friction tape and the conductor will move some as normal, but not pull itself back into place if it is out any real distance from the jacket. Be careful not to apply any adhesive directly to this wire or any wires in general under the friction tape. Liquid E-Tape protected wires can have adhesive attached to it, but otherwise it is better to let the friction tape attach directly to the conductors as it will not rip off their insulation. The friction tape will be strong enough to hold the wire in it’s place and prevent the jacket from bunching up or spreading apart. Next apply a generous amount of adhesive over the friction tape. This will serve a double purpose. First it will allow the rubber splicing tape to bond with the friction tape, and second it will act as a somewhat flexible hardener for the friction tape in much the same way as application of rosin or epoxy on fiberglass sheets works.
If you are not repairing a large hole or cut, friction tape is not necessary skip it’s step and start with Liquid E-Tape in the cut, than apply and let set up the adhesive to the jacket. The adhesive should extend at least 2" past the end of the cut, and up to 4" depending upon the cable thickness and amperage. Next apply self-vulcanizing rubber electrical splicing tape to the adhesive. If you are using rubber cement, you will need to wait for the cement to completely dry or it will burn thru rubber splicing tape and reopen the hole no matter how many layers of tape you put on it. Otherwise with adhesive you need to allow it to set up because if still wet it likely will not complete drying and might not allow the tape to adhere sufficiently or tight enough. Rubberized electrical tape will permanently bond to itself but not the cable jacket thus the need for adhesive. It will provide a water tight, and electrically intact and safe protection over the repair in sufficient thickness as required. This needs to be as thick as the cable jacket and extend for at least thee times the diameter of the cable past the cut. Normally this would mean three stretched and tapering layers over a SJ cable or more on a SO or SC cable. You stretch the tape until it either changes colors or becomes half width, and if it has a plastic tape covering over the rubber splicing tape, you do have to remove the plastic as you apply the tape. Also if you do not stretch the tape sufficiently, it will not vulcanize to itself, and will probably fall apart with time. Start at the cut and work off to one direction, than back towards the center and to the other side. Continue wrapping the cut in a tapered pattern meaning the second layer will end ½" in from the layer below it. This will allow for the cable to be pulled without snagging or flex easier. You are looking for a rounded or smooth repair. Should the tape break as you stretch it, apply the next section, start wrapping the tape again near where it broke, wrap the tape back on itself to cover the end and starting seams than continue on. The goal in rubberized electrical tape as with any taped repairs is to only have one seam - the end of the tape where it is cut exposed, where you start wrapping and where it breaks should be covered by the tape completely. After you cut the tape, stretch and push to blend the end of it into the repair so the seam well adhered and not as easy to snag. Three layers of Rubberized Electrical tape would be about the norm for SJ cable.
Apply a layer of adhesive above the rubberized electrical tape and allow it to set up. Extend the glue 1" past the rubberized electrical tape. Apply two layers of Super 33 tape atop the glue and extend it 3/4" past the edges of the rubber E-Tape. The Super 33 will provide abrasion resistance to the otherwise too soft rubber electrical tape. If you attempt to apply more than two layers of Super 33, there is an increased chance it will with use loose it’s bond with itself and become unraveled. Stretch the Super 33 by about 1/3 it’s width. Apply a thick layer or two normal coatings of Liquid E-Tape over the electrical tape. Wait for the first layer to dry before applying a second coating of Liquid E-Tape. This will complete the repair and provide extra weather and abrasion resistance. For added abrasion resistance, you can apply a very light layer of adhesive atop the Super 33. Allow it to set up and almost dry before adding the Liquid E-Tape, this will better bond the Liquid E-Tape to the repair. With use it might be necessary to apply more Liquid E-Tape over the repair or use cable paint such as a electrician/linesmen might use if you can find any.
These are the methods I have developed and have been using for cable repair for about 5 years now professionally. They work very well to protect the cable and are permanent. If done properly with a taper, the repair will not be overly large or too seriously effect it’s flexibility.
Never trust anything that is just taped together as a repair. This is a temporary repair at best and possibly covering something that can be dangerous. All it takes is a little moisture, heat or exposed conductors and your wire given sufficient amperage and voltage can short causing all kinds of problems if not a fire. Proper repairs are very necessary if you want to continue using the cable without cutting it and making it into at best two usable sections. If not the above or an even more proper linesmen’s splicing covering method, just cut the cable and make what ever you can out of it. Electrical tape alone does not make a permanent repair, it just makes me suspicious. All repairs need to be inspected by trained personal looking for damage to the conductors before it should be repaired permanently than placed back into general use stock. Should you need to do an in the field repair to cable, it is a nice courtesy to provide a strip of colored electrical tape near the repair in a yellow orange or red so such a repair will be noticed after the production. An alternative method especially for feeder cable would be to apply the friction tape and rubber tape as above, than use heat shrink to form the outer protective skin over the repair.
Brian Shipinski