I have to caution you against doing this project. I will attempt to provide a lot of information on how to do it, what’s possible in technique and what to watch for in general by memory, but also caution that you need supervision in doing so and should not mess with the fixtures as planned.
In the question of SO verses SJ
wire, which would be better as a
fixture whip, it shows a lack of understanding of
wire types used in electrical practice which also provides red flags to me in the wish to re-wire fixtures or remove the
asbestos from them. Your intent is good but needs training and supervision in the practice of it. SO or SJ - both rubberized 90c
wire are better than a thermoplastic SJT
wire in some ways. As opposed to thermoplastic
wire, grade S cable will not melt down, instead it will become brittle and flake off in entire sections. Dielectrically there is not much insulating qualities to it once overheated, but at least as opposed to a melted
insulator, it will not be quite as dangerous. It however like SJT or SJE however could still start a fire when it gets hot enough. Such types of
wire above are specifically not recommended for use within a
stage lighting
fixture unless part of a
PAR can or similar
fixture which has a lot more cooling and open area within it. Even than, such
wire is not the best solution. Do not use extension
cord no matter the type SO, SJ, SJE, SJT,
SPT - any multi-conductor cords starting with a “S”
wire as
stage lighting
fixture cord should not be used.
Beyond this, follow very closely any mention of
asbestos here, on stagecraft and other places, it is not something to be just removing by way of a few precautions taken. This removal project is potentially very dangerous to you and many others in the future that visit your work area. Such problems won't be seen immediately, instead they would show up 10 or 20 years from now. This is not a recommended project to be doing as a student. Have someone or a disposal company instead remove it and clean the
fixture for you, than seek qualified supervision in attempting to re-wire the fixtures. Rewiring stuff without supervision is all a question of some potentially dangerous thing you forgot or did not know better than to watch out for. A second pair of eyes on what you do is always good even at least if only trained in general and not specifically for doing this.
Another option:
Otherwise, should it be determined that the fixtures are unsafe to be working on due to the
asbestos, an option in not fighting the authority and sense of not risking your health for a hundred dollars worth of antiquated inefficient lighting
fixture, would be to instead go with the flow of not service the equipment in question. Instead remove the
lamp cap from the
fixture and have it properly disposed of without attempting to remove it’s wiring. Save the rest of the
fixture perhaps in all but the
lamp cap, it’s wiring and
plug. If the
fixture is an antique, it should not be used and not require wiring within it. An antique
fixture requires removal at least of the
whip, and possibly qualified removal of the rest of the
asbestos, but otherwise if it’s old but intended to be used, having all it’s original parts should not matter in functioning thus getting rid of the
lamp cap and other components that require exposure will not be a problem.
Such parts you get rid of can possibly be replaced
thru the company that made the
fixture if still in business, other companies making often extremely similar equipment or old
fixture parts dealers that might
stock old parts such as
Hub Electric. Often if not the same some slight modification will be necessary to retrofit a
lamp cap to your style. This can get complex but once the first one is figured out, subsequent ones are much easier. Study and take photos of the old lamp caps before thrown out. Slight modifications to it’s fit or how the
base mounts to it’s plate sould be fairly easy to tinker with making work properly. Where possible buy the proper replacement parts or where other parts cannot be made to fit, your fixtures might not be worth the effort. This allowing the
lamp cap assembly to be disposed of, while a pain in the rear in re-fitting the lamp
base to a new cap would allow you potentially to less fight the problems of removing the
asbestos and still keep the
fixture. In retrofitting another type of old cap to a
fixture, much modification to the
lamp cap will be necessary anyway to modernize it, starting with a new
lamp cap assembly or using an old one in the end will be almost the same effort needed. This could be a good option for replacement as opposed to needing to work with the
asbestos. Even I would think twice about exposure to
asbestos in ways I allowed myself to in the past.
Below Are Some Notes On Old Radial Style
Leko Rewiring. (This is for discussion in technique, parts and things to watch and not a step by step guide for those without training and supervision in doing so. There is many steps and techniques that will without a doubt not be mentioned or noted dependant upon the individual
fixture. Trained eyes in helping with and supervising the project is necessary to
wire a
fixture safely.)
Wire to be used or avoided:
14ga
wire on grade S cable is rated for 15 amps = 1,800w. On 200°c heat
wire, it's commonly used for 2,000w loads. Are we sure this is the necessary
gauge of
wire to be using as recommended above???
If the
fixture is only rated for 500w, 18ga SF-2 silicone coated (sometimes Teflon) heat
wire (200°c rated) would be sufficient. It comes either as a silicone
wire or a silicone
wire with fiberglass braided sleeve over it. If given the option, go with the fiberglass sleeve over individual silicone coated conductors as it adds an extra layer of protection over the silicone
insulation.
Given your
fixture can probably also take a 750w lamp, it might be more safe to
wire it with the more commonly used SF-2, 16ga
wire. This is what
gauge most Lekos are wired with. This would be a 19
strand wire which is more flexible in a
cord whip than the otherwise higher temperature rated TGGT (250°c)
wire that is less flexible and not recommended for a
cord whip. Good
wire the TGGT, but not needed for this purpose. This might be the type and temperature
rating on some newer fixtures, but as opposed to commercially available TGGT, it would have smaller strands and more flexibility to it. In 14ga heat
wire while it will certainly carry the load would also be less flexible in a
fixture whip which is why it would not be best to be using due to wear and tear. Same reason one could
wire a
fixture with 12ga even 6ga heat
wire but would not wish to beyond cost of the
wire. There is no benefits to using a 14ga heat
wire on a
Leko unless rated for over 1,000 watts.
Conductors Colorings:
Given your fixtures will probably have a medium
pre-focus type of
polarized lamp
base, (P-28s) you will need a white, black and green
conductor. That hot (black)
wire must be wired to the hot
terminal of the
plug which is the center contact of the lamp
base. Otherwise should someone attempt to remove a lamp while the
fixture is live, they will get a
shock. This is common to all but double ended
RSC type (R-7s) lamp bases and
bi-pin or dual contact lamps in general. The reason for not needing color coding hot/
neutral on such lamp bases like a
par can, or modern
Leko is they don’t have one of it’s conductors going to the outer shell of the lamp
base, hot verses
neutral does not matter on them unless of a special type required by the lamp itself. Anything using a screw
base,
pre-focus base or single contact bayonet
base amongst others is dependant upon the
neutral going to the outer shell of the lamp
base and hot going to it’s center contact. Ignoring this is dangerous.
If a black heat
wire is not available, you can permanently otherwise color one of two white wires by way of paint marker or Sharpee as long as such coloring runs the length of the
wire and is clearly different from the other
conductor. A single or double stripe is sufficient as long as it runs the length of the
conductor. While no longer necessary by code to run the length of the
conductor, in a
fixture whip as opposed to it’s terminating ends, such a marking would be a good idea and within the spirit of the code. It is not worth attempting to color the entire
conductor. Part of the
NEC stipulates professional quality of work and you won't be able to get a
wire evenly black with just a marker. Cable companies dye the
wire but this is not something easy for the end user to do to silicone or fiberglass.
Your
ground wire does not have to be rated for the full 200c, but should be the same
wire gauge. It should be green and using a stripe of color is not within code for doing so. Either yellow/green (Euro) or entirely green is the only option for a
fixture whip. Buy a pre-dyed
ground wire. It is not required to be the same
wire gauge - you can step it down one in size, but in general it is a good idea to make it rated at capacity. The concept of stepping down the temperature
rating of the
ground wire would be something visible about the conductors that would show if they are getting overly hot. One would much rather note your
ground wire in melting down than the hot wires doing so after the fact. It also won't be as near the heat source. Type K Teflon Green 150c FEP
wire would be sufficient for a
ground. Having such lesser rated
ground wire within the
fixture will help in the
fixture’s at least yearly inspection to note other problems where over heating needs to be found the cause of.
Outer Sleeving Types:
On the outer covering of the
whip, normally type "0" fiberglass sleeving - 5/16" is the cable
whip outer covering is used on lighting fixtures to
cover the heat
wire conductors. I like a 1/4" sleeve better - less chance of snagging. Normally all fiberglass sleeving will have a internal foil to it which helps reflect heat and could offer electrically a further layer of protection in carrying a short to
ground instead of by way of your
hand. While not really designated for this purpose that I’m aware of, I have seen this to be the case at times that a short will conduct
thru the metallic liner of fiberglass sleeving for good or bad.
There is other types of sleeving that can be used on the
fixture to protect it’s conductors. Braided Polyester Mesh Sleeving is commonly available and used for a low cost retrofit. It is rated for only up to 257°F as opposed to High Temperature Woven Fiberglass Sleeving which is rated for 1,202°F. In such Poly sleeving and while both types snag, it has a more open weave to it that tends to snag easier. I’m not a great fan of this type of sleeving but many do use it effectively.
A third type of sleeving available is not cheap but which solves the problems of wear and snagging is vinyl or silicone coated fiberglass sleeving. Vinyl coated fiberglass sleeving while not rated for as much in temperature and less flexible is a good somewhat economical
fixture whip sleeving product where otherwise replacing fiberglass sleeving frequently. Silicone coated fiberglass sleeving on the other
hand is really useful in both temperature and abrasion resistance. Were it not very expensive, it would be a really good other than limited application alternative to normal fiberglass sleeving.
High Temperature Multi-Conductor Cable Whips:
Another less used option would be to go with a "Rockbestos" type of multi-conductor cable. A few companies sell various versions of it and I believe actual Rockbestos brand is off the market though might still be available
thru Altman or perhaps Mole Richardson. Basically given a
wire gauge, it is like a SJ cable, only high temperature based in having a
ground,
neutral and hot within a outer
jacket, all of which that is rated for 200c. Rockbestos is really good stuff. Some of the
fixture whip multi
conductor cable most other especially theater supply companies sell that is Euro based, it will work but is not as good. (My opinion.) It tends to have problems with oil from
fog fluid and at times heat in cracking all the way down to the copper. It just does not react well to compression, abrasion and other things a more natural outer
jacket/inner
jacket with fillers type of cable will better deal with over that molded around the conductors. This especially will be the case should you nick in slightly cutting the
jacket of the heat cable than pull on it. Such Euro heat cable/
fixture wire will often be found on
PAR can whips of a higher quality than SJT (75c) also used on them otherwise normally, or on other than domestic movie/location lights. The heat
wire used on Kupo fixtures or available
thru them might be a better alternative in being both thicker and different in style. Such heat
wire is under study. Domestic movie/location lighting will either use Rockbestos or at times SO cable where it is not directly exposed to heat. Normally on the Euro type heat
wire/
fixture wire, the silicone will be molded around a set of frequently brown/blue/green-yellow conductors. Such cable will be rated for anything from 105°c, 150°c and 200°c, when buying it verify what the temperature
rating it is. Rockbestos where still available has a outer sleeve that is not molded around conductors and is rated for 200c. Such a 200°c temperature on your conductors would be a good temperature
rating to use on a
Leko and every
bit as similar to SF-2 in heat
rating - only with a outer
jacket more resistant to abrasion or snags. Anything in temperature
rating less could melt down and cause problems.
Heat
wire or cable in general is available
thru most theater suppliers, cable suppliers and of course McMaster Carr. A cable is an assembly of multiple - including three conductors within an outer
jacket as opposed to a
wire with only one
conductor. A
fixture whip within a fiberglass or other type of sleeving as an assembly of conductors than would also be a cable to some extent in having a protective sleeving over individual conductors. While done at times individual conductors should not be used without a protective
jacket or sleeving over them, nor should a
fixture be used with such
jacket or sleeving having serious holes or cuts in it. Various glues such as Plyobond can glue together in preventing fraying a small cut or hole, but use of a fiberglass sleeve that is overly damaged defeats the purpose of a protection of the conductors and must be replaced.
Things to check on the lamp
base:
Your lamp
base if Medium
Pre-focus (P-28s) will normally have screw terminals on it. This will allow direct termination of the replacement
whip conductors to the lamp
base without replacement of the lamp
base. Before you attempt this, determine if the lamp
base is worth saving. Does it have arcing and other damage to it's center contact? Is the
pre-focus locking ring working properly, is the center spring providing enough tension and in general is it in good shape? While you can re-surface such a thing as a center contact, that's another project than rewiring and often might be more cost effective to just replace it. Other things to watch for would be rivets tight and not allowing the sell to be loose,
porcelain not over heated or breaking and terminals the screws thread into not loose.
Resurfacing of things like shutters and types of spray on graphite
etc. or various paints would also be another topic of inspection or work, along with cleaning the lenses or inspecting the grade of them to be done while working on the
fixture as a project.
In this same concept, before you attempt to re-install an old lamp, have a look at it's center contact. This especially if you do replace a lamp
base. Put a bad lamp into a good
base and you just destroyed the new lamp
base. Put a good lamp into a bad lamp
base and it won’t have much better results. Start swapping out semi-used lamps between semi-used bases if not all around in good condition and you
gain a lot of stuff with new problems added to them. The lamp should not show blackening or any arc welding on it’s contacts, the brass coloring should not be blue or white, or otherwise discolored much more than normal for brass, the cement should not be cracking in having large gaps or missing parts of it, the
filament should not be sagging or coming loose from it’s support structure and the
globe should not be blackening or otherwise misshapen.. The
base contact points should be a smooth or semi-smooth surface and one without pits, discoloring or melted areas.
New lamp bases are standardized parts in design so it won’t matter if really old or new or what brand it is, they will all fit. Replacing the lamp
base when in doubt given they are not expensive is a very good solution.
Check also the fiber
insulator pad under the lamp
base - washer like part between the lamp
base and the mounting bracket for it. Hopefully it's a fiber one and not an
asbestos one. Should it be blackened and crack rather than flex - replace it. Such things might be sold separately or come with new lamp bases. A good
insulator here is very necessary. One that is damaged also does not dielectrically protect well. Fiber of a proper high temperature and
dielectric resistance can be bought and cut to fit separately in sheet form if not otherwise available.
Dielectric resistance meaning the amount of resistance to short a material has.
Terminating the wires:
On terminating the hot and
neutral to the lamp
base, do not attempt to just mount the wires directly under the screw
terminal. As such
wire heats up, it expands and contracts causing what was once a tight connection to loosen. You will almost never find an instance of purpose to have a stranded
wire directly under a screw
terminal without a plate,
ferrule or
terminal between it and the turning head of a screw. Don't over-tighten your screws either, this causes resistance due to the pressure and can strip the screw. 1/4 turn past finger tight is the normal rule.
Tinning your wires around the screw also is not a great option in both ability to tin heat
wire and the solder potentially melting and having the same problem as without of the conductors settling.
In the past there was a type of both
ferrule and washer that would encase the
wire within a circle and compress under the screw head. Good option if you can find a source for them. Perhaps Allied Electronic, Mouser or Newerk might have them if you really search. I have seen such a part still available but forgot the source. Such things were commonly used in the past.
Otherwise you will need a crimped
ring terminal to terminate the
wire to the screw
terminal of the lamp
base. Your normal vinyl insulated ring terminals won't work well even with the plastic removed in a high temperature application. Under a lamp
base, you must have a high temperature
ring terminal. McMaster Carr is a good supplier of them. You don't need the 900°F ring terminals, the 600°F terminals will be fine and you do need them. Dependant upon the lamp
base, it will either use 6-32 or 8-32 screws on it - most likely 8-32. Size the ring terminals for the screw stud size and
AWG (American
Wire Gauge) of the
wire. Use of the wrong stud size of
ring terminal or wrong
gauge of
wire in a
ring terminal type can come loose on the
terminal or allow the
conductor slip out in becoming a
safety hazzard and in general problem with badly crimped terminals done on the cheap. Due to the design of a P-28s lamp
base, you will need to be careful of using a
ring terminal due to it’s longer length, larger size and not being able to
bend around a more or less curved surface inside the bottom of the lamp
base. They were not really designed for use with a
ring terminal, and in general one should be careful to ensure the
wire or
crimp does not get pinched between
base and
insulator.
Crimp Tools:
To
crimp any and especially these ring terminals, the standard hardware store bought multi-strip/
crimp tool won't do a sufficient job on a steel or in practice any type of
crimp terminal.
Throw the local hardware store crap away. This especially in the useless "insulated
terminal”
crimp tool jaws. This is even the case with a overly large tooth of a multi-tool
crimp that still more crushes the
crimp than displaces material within it. Insulated crimpers just crush the
crimp terminal and don't displace the material of the
crimp in keeping it similar in size - only the space
wire is allowed to be within is compressed around the
wire. Very bad connection in general that of a flattening out of the round
crimp or
wire. In a crushed
crimp, some of the conductors towards the edges will have less pressure on them than others. Most hardware store multi-tool strip/
crimp/screw cutters are of the badly
crimping - much less badly stripping type. Avoid the use of them. Also in leverage you want your
crimp jaws to be close to and on the opposite side of the plier pivot for the best use of leverage.
You will be needing something with a tooth and saddle to it which will
send part of the
crimp jaw inward into the conductors. Such tools are frequently called "Stakon
crimp tools." They have a double or single jaw (with insulated crimper on the single jaw version) and both types have a cutting blade on it's tip. Very standardized type of tool amongst most manufacturers. Klien #1005 and #1006 would be examples of them.
Proper
crimp tension would have a crimped
wire you could yank on as much as you want and it won't come loose or break strands to. On a 12/3 cable, you could screw them to a wall and climb the cable without the crimps coming loose. Always after
crimping your
terminal and while the tool is still compressed pull on the
wire to verify that your
crimp is tight enough. Always put the seam of the
crimp into the saddle of the
crimp tool.
Crimping the seam with the tools jaw will result in
wire that can pull free or be cut. Some amount of practice will be necessary to balance between something overly tight which damages the
ring terminal and conductors and a sufficient pressure that the
wire cannot come out.
Of the above #1005 single jaw and #1006 double jaw tools, the double jaw
crimp tool works best with 10-12ga. crimps and 18-22ga crimps. The single jaw tool works best with 14-16ga
crimp terminals. If you grind off the cutting blade tip, both tools work well with
crimping old style Union brand
stage pin flag terminals - especially the #1005 type. Any Electrical supply store will have these tools available or know what a "Stakon" tool is as a brand name for a standard type of
crimp quality tool.
Insulating the terminals:
Once these terminals are mounted on the wires, you should install either high temperature fiberglass electrical tape or high temperature teflon tape over the
barrel of the
crimp. A
roll of 1/2" size three layers thick works well. This will in addition to the fiber
insulator under the lamp
base protect against shorting. These tapes are 3M normally products - McMaster Carr again as one supplier. This tape - especially the fiberglass tape will both insulate the berrel of the
crimp and prevent the fiberglass braiding over the
conductor in the
terminal from fraying. Width of the three layers of tape should be 3/4" and tapered.
If possible also while not necessary, install some 1/8" silicone coated fiberglass spaghetti tubing for double insulating over the first three inches of the wires coming off the lamp
base. This will both prevent damage due to any abrasion and double insulate for heat where the
insulation is hottest and normally melts down first. The McMaster Carr sold - silicone coated fiberglass sleeving - same type of thing as above for a
fixture whip but in a smaller size. 12ga tubing would work well.
Attachment of ring terminals to lamp
base:
The
ring terminal attachment to the lamp
base needs to have a good contact. If your screw terminals are discolored and in general looking rough, seek replacements for them. Brass screws will be necessary due to heat and conductance. Avoid
Phillips head screws for this purpose. It is harder to get them to the proper tension without stripping (especially with a cheap or stripped screw
driver), and the amount of push down pressure required to get them tight could damage the lamp
base in doing so. Also if not already available, add a silicone bronze external tooth lock washer under the head of the pan-head screw. This will help prevent it from coming loose. Do not use anything other than brass or bronze for a
terminal. This especially not zinc plated or even stainless steel hardware for what conducts in a high temperature application. Also do not use chemicals such as even high temperature thread lockers in this area - they will not help
current to flow. Deoxident and other types of oxygen reducing or surface cleaning products are okay but not needed in most instances. Often such products will also lubricate the contact which is bad for the concept of a
terminal that should not come loose.
Other screws:
On the subject of screws, in mounting the lamp
base, or in general about the
fixture 18-8 at least if not type 306 stainless steel screws, lock washers and nuts are of a major advantage over that of anything zinc plated in a lighting
fixture. Should your screws show any rust or discoloring, replace them with Stainless Steel hardware. Otherwise they will tend to rust even more. Stainless will also have less a problem with dissimilar materials connections such as where a steel screw is threaded into a aluminum body. Avoid also black oxide coated hardware inside the
fixture, such screws often rust easily. Avoid also nylon insert nuts (nylock nuts), the nylon on them begins to break down at about 221°F which would than prevent any lock
nut advantages of such hardware. Instead of Nylock nuts, use side lock or top lock nuts where possible otherwise other types including
crown lock nuts. In the case of a screw to
nut fitting, do not attempt to use a stainless steel thread deforming
nut (top lock/side lock) with a stainless steel screw. Such screws have a lot of surface hardness to them and especially on a smaller screw will strip and break rather than deform the threads of the screw in doing a proper job of locking. Use either a stainless screw with a zinc thread deforming
nut or zinc screw with stainless thread deforming
nut. An alternative to this would be to use a stainless steel
nut with a external tooth lock washer attached to it. This will to some extent prevent coming loose especially when high temperature Threadlocker is used.
In general for all bolts use external tooth lock washers over any from of spring lock washers, or at least internal tooth lock washers under the smaller size round head or fillister head screws. Much better and distributed gripping
power. High temperature type threadlocker is also a good idea in all applications other than to the lamp
base electrical contacts. Should your screw head be in direct contact with the
porcelain of the lamp
base, be very careful not to over torque that screw. Also use a teflon washer or other high temperature padding washer under the screw head for this metal to
porcelain contact to prevent breaking or chipping. Round head screws are more commonly used in a lamp
base than pan head screws. Be mindful of what type of screw was used and what properly fits within a
porcelain lamp
base because use of a screw head which is too large such as on a pan head screw while it might fit will either require downsizing of the proper screw or could break the
porcelain around it. A 18-8 stainless steel slotted round head screw will be the screw probably provided when new or at least should be the better replacement. On other screws such as the ones to adjust the
lamp cap or sheet metal ones attaching the
lens train should be observed for corrosion and replaced also replaced as needed.
Grounding:
Your
fixture if old and
asbestos, probably won’t be grounded. You need to install a
ground if not already installed or install a new mounting for it if installed in the wrong place. The proper place to attach a
ground on most fixtures is to the adjustable mounting plate of the lamp
base. Given this part for the most part
floats within the
fixture due to adjustment needs, attachment to other places will not provide as solid a
ground where it is most needed.
Easy enough to drill and tap for a
ground screw the plate that holds the lamp
base. Don’t attempt to just toss the
ground terminal under something already there for a hole or screw. Normally there is lots of room on the mounting plate to do so. Do not use cutting oil in drilling or tapping the plate either. You want this to conduct and oil will not help in doing so and could pose a fire risk or
smoke up your
reflector and lamp. On a
ground screw, it should not be stainless steel since it does not conduct that well as a material. Zinc is ok but I like using actual grounding screws for them. Hex head slotted thread forming 10-32 x ½" grounding screws such as Raco makes by the hundred pack. The green coating to them both tells what it is and helps them as a surface treatment to conduct. Such screws as yet have not had problems in taking the heat or corroding due to dissimilar materials attached to. Driving them with a 5/16"
nut driver is also much easier than driving them with a screw
driver. Use a Stainless Steel external tooth lock washer under it’s head also. A loose
ground is all a question of path of least resistance in either you or the loose
terminal being a better path to grounding out a short. Better to ensure it won’t come loose - ever. In doing this part of the regular maintenance of any
fixture should be to verify that you can’t move the
ground wire around in it’s attachment. A loose
ground wire attachment does not conduct as well. Since your lamp
base mounting plate will probably be aluminum, threading the plate for the
ground screw can when over tightened or even tightened sufficiently allow it to become stripped. Better to drill
thru this and install a top lock stainless steel
nut on the opposing side of the
ground terminal. (I’m not a fan of rivets for grounds - they loosen especially if aluminum.) As with above for the lamp
base terminals, the
ground wire should be terminated in a
ring terminal. Since this area has less direct heat on it, a more normal non-high temperature
ring terminal as long as un-insulated would be sufficient. In this case, a 16ga x #10 stud un-insluated
ring terminal.
Strain Relief Types:
Your
fixture if
asbestos probably did not have a
strain relief to it’s cap. Instead they used brass grommets most often for each
conductor. You now will need to drill out one of these holes for a proper
strain relief. 3/8" NPT (National Pipe Thread) - two screw
cord grip strain reliefs are the best to replace such things with. Plastic
Heyco type strain reliefs tend to become brittle with heat and anything in weather proof rubber
grommet grip or other more store bought types in ½" NPT are going to require a 7/8" hole which is a
bit large. Make sure that any metal projecting inside the
lamp cap will not get in the way of operation of the adjustment or pinch the wires.
You can use a ½" NPT two screw
strain relief as a alternative but it’s not needed in size and will possibly be too large a hole under the clamp unless old style in having a smaller hole shape to clamp the cable. 3/8" NPT two screw strain reliefs are available by way of
Altman and their distributers and by way of other suppliers for a 3/16" to 1/4" gripping clamp of 3/8" NPT size. The ones listed in the McMaster catalog are ½" NPT types even if listed as 3/8". They will
grip a 3/8" cable but not a
fixture whip as well - see below on bulking it up in making do.
If you buy the
Altman strain relief, give it a good go on a soft bench mounted
wire wheel. Otherwise the very rough cast = made in China
strain relief will have some very sharp cast edges to it. The currently available
Altman strain relief also does not have a very good thread class fit to it either. In other words, the
nut will be very loose on it’s threads and potentially come loose in the future with use. Use of high temperature
thread locker on this to help prevent this problem will help, or don’t use what they offer seek other sources for such a 3/8" NPT
strain relief. Another option would be to thread the
lamp cap’s hole for 3/8" NPT but only use the beginning few threads of the
taper tap so it is a tighter
fitting and more close to that of the China crap. Than to use the
nut to lock into place the now double nutted
strain relief threads. This with High Temperature
Thread Locker would probably work well. There are other versions of a two screw strain reliefs if not even two screw/liquid tight
grip strain relief combinations available such as for the
Altman 2000L
Fresnel fixture that are much more refined. They would work well.
Another option that is oddball and slightly large for the top of the
fixture but would work well is the GB brand of store bought - Menards,
Romex type
flat cable
cord grip strain relief. Such a
strain relief will be rough cast aluminum and have a rubber clamp that is in a oval in shape small enough to
grip your conductors. There is enough rubber on it that it once gripping the cable probably won’t have as much of a problem with being damaged by the heat. This granted a larger hole needed for the ½" NPT threads. Tapping your hole would probably also be a good idea for this
strain relief for the double
nut technique of preventing strain reliefs with a lesser class of fit (looser tolerance between thread and
nut) from coming loose.
Other types of
strain relief used will be the
Heyco (there is other brands)
line of nylon
strain relief. Some will be found on rock and
roll par cans in being “liquid tight” nylon. Such strain reliefs - commonly the metric PG-11 size or the ½" NPT size don’t work well with the heat of a
Leko. Both it’s screw threads and
nut will melt some in becoming loose or brittle, and it’s rubber
grip will break down with heat. Two better versions of this type would be the high temperature - grey ones, or the while still normal nylon,
Romex/
flat cable gripping
strain relief. As above, the larger amount of rubber in an oval shape will
grip the cable somewhat better
grip and be less prone to getting too hot - though in a non-high temperature
grip have the other more normal problems. Normal steel or aluminum “liquid type” moisture proof strain reliefs that have a rubber insert in compression that grips the
wire such as the Amfi type or Neer will work well when properly sized but be fairly heavy and bulky. They are not much used and in this type of
fixture as with the above GB or
Heyco types probably not a good solution due to the heat on this compressed rubber gripping
strain relief. They all work well on other types of
fixture.
Another
Heyco type commonly used on Lekos would be the “
Snap in
Cord Grip Fitting.” These strain reliefs compress and fold the
cord within a two piece relief when inserted into the proper sized hole. The best hole for them is a oval shape not a round hole, though a properly sized round hole will also often work in gripping but not preventing rotation. A slight downsizing of such round holes will be necessary to prevent rotation of the
strain relief than. A improperly sized hole will allow the
strain relief to pull loose, allow the fiberglass sleeving to slip or crush conductors. Each type of
strain relief will have a code printed on it such as 6P3-4 used on a
Altman 360Q cap. This designation is important to match for replacements as each determines either
flat or round
cord and the size of the hole the
strain relief is designed to fit in. Check the
Heyco website for proper hole sizes to match up with the
cord grip used on a retrofit situation. These strain reliefs are hard to work with unless you have the specially designed
Heyco pliers to compress and insert or remove them. As above with ring terminals and nylock nuts, nylon becomes brittle when over heated. Replacement of them once removed is frequent. When properly sized, it is a good option and the only one you should not use the fiberglass tape on mentioned below.
Installation of the
wire in the
strain relief:
A trick to doing your
strain relief is to coat the end of the fiberglass sleeving over the conductors with a 1.1/2" section of the fiberglass electrical tape at least three layers thick. This should stick outside of the
strain relief by about an inch so as to prevent flexing of the
wire too close to the clamping part of it that otherwise could cut into the conductors while flexed. The fiberglass also helps prevent against wear at the
point it flexes or is gripped. Such fiberglass tape can also be used to bulk up a slightly wider
strain relief hole. Installation of the tape should start and finish under the clamp so as to prevent it from un-wrapping.
Plugs:
Finally what is not at this
point much considered but something to consider is at the
plug end of the
fixture. First read the instruction sheet that comes with each new
plug. Don’t attempt to save the
plug that was on the
asbestos whip. Not worth your time nor effort. Buy a new
plug and read it’s instructions especially where it comes to proper
strain relief. You would not believe how many professionals in the industry have no idea beyond safe (Gee as long as the black
wire goes somewhere not the
ground and
ferrule used or not) professional wiring how to finish their professional job by way of doing a proper tension and clamp setting
strain relief. Stuff like if using 12/3 SJ cable on a
stage pin plug, both
strain relief fittings used in the round to really clamp that cable tight. Don’t know how they clamped it all the way down without breaking the
plug but once there all the rubber in the
wire was once under pressure displaced to an extent only about 1/32" between conductors in the area under the
strain relief was left. This area now with a minute amount of
insulation between conductors tends to get flexed a lot in potentially cutting
thru what’s left insulating them = I would not
call that professional given the professional wasting time and money and potentially injuring someone in the future by way of his or her “professionalism” was too professional to read the instructions for proper
strain relief or have a thought about over tightening screws or strain reliefs. On a
Bates style
plug, one insert on the
flat and one on the round would be proper for three 16ga heat wires within a fiberglass sleeve. Oterwise, there is a instruction
manual to determine what is proper for other types of cable. “I thought” in being wrong by way of too lazy to learn or consider and test or “I was too busy” to do it right should never be an excuse where doing electrical work properly. This even if only on a
strain relief. Impossible witout double
wire ferrule to fit two 12ga wires within a
Bates style
plug, much less one cannot fit two cords within it’s
strain relief. The
Bates plug and it’s clowns is a good design in
fitting many types of cable within it. Other types of
stage pin,
Edison and Twist will take more observation and instruction reading to ensure your cables are properly gripped without being either too lose or tight.
Read the instructions for installing a
plug before installing it = no matter the type. Sometimes if the
plug does not include an insert, it will be necessary to add some tubing or
friction tape under the
plug so as to bulk up the cable. Such a option is fine also. This as long as you can pull the outer
jacket of a cable and it is both not loose within the
strain relief or pulls out of it, and does not crush
insulation between conductors. Always use commercial grade plugs also. It’s not your
house so some crap but cheap
plug should not be used.
After this there is a concept of
stage pin plug.
Twist lock and
Edison have clamps that don’t twist
wire around a
terminal or clamp them directly under the threads of a screw. They are different. If using a
stage pin plug, and given you are not using 12ga
wire the terminals or ferrules for under the
terminal are provided with, you should not be using such things with a 16ga
wire. When you install 16ga wires inside a 10ga hole, it tends to have a lot of slack within it and will not
crimp or otherwise ensure a proper termination.
Seperation at this
point between
crimp type ring terminals and
ferrule type
stage pin plugs than is necessary. On
crimp terminals even flag terminals, 16ga flag type ring terminals are a McMaster Carr type thing as with other 16ga #8 stud type
crimp terminals.
What’s provided with a
stage plug is a 12AWG
ferrule. This is for use only with 12ga
wire. If your
fixture is using 16ga
wire, it in inserting the conductors under a larger
terminal only asks for that ferule to be useless. First because in not encasing the
wire strands, they fan out under pressure and
settle thus don’t conduct well if not even break. The
ferrule itslef in having nothing behind it frequently gets cut
thru by the screw
terminal attchment. There is an option of folding in half your
fixture wire so in a concept of every time you double the size (fold in half a single
conductor) the resulting size of
conductor will be three sizes larger in size. Thus in the above, were one to fold a 13ga
wire in half, it would than be 10ga and not fit within a 12ga
ring terminal.
While ignored, often it will be noted that on a
Bates type of
plug that the screw will cut
thru the 12ga
ferrule than proceed in turning tight also cut
thru conductors of the
fixture wire. That’s a bad thing in both not being able to get your wires out of a
plug and by way of cut conductors - higher resistance. Cuts
thru the conductors of the
wire either by way of the screw or sharp cut
edge of the
ferrule under clamping pressure
Just as with a
ring terminal type of
plug or even flag
terminal type of
stage pin plug, by way of McMaster Carr, there is proper for the
wire used sized ring terminals, there is also properly sized ferrules available. Buy an insulated 16ga
ferrule than sleeve the 12ga
ferrule over it. This than in having two ferrules resists a cutting trough by way of the screw and in encasing the
wire and also being the proper size for the
plug’s
terminal will fit correctly in a non-damaged way.
In termination of the
plug, follow
strain relief instructions - including that detail of not having non-outer jacketed conductors under the
strain relief - follow the strip
gauge to the
plug, and add for a
fixture a second properly sized
ring terminal, flag
terminal or
ferrule.
Some notes amongst many on
fixture working on type stuff. Hope it helps, and as one might see it’s not quite as simple as it could be to just re-wire the thing. Good project to work on given supervision once the
asbestos part is taken away, but not something to just “have at” in having a few free hours short of having the proper parts and techniques to do it properly. Many more details I am sure I forgot to mention.