What is wrong with this picture
- Thread starterMayhem
- Start date
JahJahwarrior
Active Member
unable to resist the offer of swag, I am thinking about the threefer as well. Ship, I am wondering, is there any possibility of something being wired wrong outside of the threefer? like, one of the lamps it was plugged into? Like, could one of the wires have been reversed or something? I would think that if something like that had happened it wuld have hurt the lamp as well as the threefer so i don't view it as likely. my other wonderment is, could the problem have something to do with the breaking of the pin? I, not knowing much about stagepins, know that the pins are varying distance sform each other. so, it doesn't seem to me that it would fit in backwards, but could there have been some other problem to push the pin in and break it? like, could the thing he was plugging it into have had some sort of crap in it's female positive end? Something to shove the pin on your threefer in? perhaps he had another broken stagepin in it 
and oncec the pin was pushed in, could it have managed to touch any of the other wires in the stagepin? because that wouldn't exactly be good
and oncec the pin was pushed in, could it have managed to touch any of the other wires in the stagepin? because that wouldn't exactly be good JahJahwarrior
Active Member
sadly, I am no expert on electricity and oxidation...but, would oxidation only occur on the hot wire if the wire was wet while operating, or would it occur on ALL wires?? if it would only occur on the hot wire, then yeah, I think that soundman could have a point with it becoming a heating element like thing...now, ,why exactly did it oxidize? i know you don't need water for it to occur, but my first thought would be operating in a wet spot or in the rain or something. can any of you answer my first question? thanks!!!!
JahJahwarrior
Active Member
could it have oxidized that much in one show, presumably one-2 days, operating three lights at the maximum rated load of hte cable for a good deal of that time, if it was in either a very moist spot, or indeed in a small puddle? or if some watter got in it briefly and although they cleaned theoutside off, the inside stayed wet? and why did only one cable oxidize? i know metals can oxidize almost instantly given certain circumstances, but could this metal have oxidized that fast in these cirumstances?
JahJahwarrior
Active Member
Pics are taken for what they are. Waiting on Dave to post them.
Waiting on them to also comment much further about pins pushing in to be a cause and other things. Getting close to one of the possibilities, just not well thought out as to why yet.
On another possibility, a short at the fixture probably won't bother the plug two or three feet away from it even if directly attached to the fixture - it would most likely bother the male plug to the fixture and the female plug attached to it by way of heat. Probably won't being an operative term as if this caused a serious overload at the threefer because of the extra current it cold potentially also take out the threefer plug. Not because of the heat effects of the short but because of the overload in current now traveling thru the threefer going to the bad fixture and to the other things attached. A question of how bad that short first in what's taken out first - the fixture and it's plug or the threefer. In any case, it's also getting close to an second if not third possibility of the threefer's failure.
Still three potential causes of it and one specific way to rule out one of them which has not been recognized yet. A second thing you might note that could cross out the second one. Given the picture however it will confound and make it more confusing yet because the neutral I had not noticed at the time is also burned up - but not the ground. Nor is the plug in any way melted down.
Only damage to the plug is in the area that holds the hot pin in place It broke in allowing the hot pin to slide backwards some. You will also probably not note but have it noted that the pin spacing on the hot pin is smashed together. This is what's necessary for a tight connection. The pin itself looks like it got heated red hot for a period of time due to discoloring. The insulation off this pin and for some reason also the neutral having this heat also flaked off.
The plug was factory installed and was of crimp type thus there is no chance of a loose set screw in crimping wire to terminal. Strain relief was tight but not too tight, and the outer jacket on the wire at the strain relief and away from it looked to be in good shape.
Any help in re-stating the observations?
Waiting on them to also comment much further about pins pushing in to be a cause and other things. Getting close to one of the possibilities, just not well thought out as to why yet.
On another possibility, a short at the fixture probably won't bother the plug two or three feet away from it even if directly attached to the fixture - it would most likely bother the male plug to the fixture and the female plug attached to it by way of heat. Probably won't being an operative term as if this caused a serious overload at the threefer because of the extra current it cold potentially also take out the threefer plug. Not because of the heat effects of the short but because of the overload in current now traveling thru the threefer going to the bad fixture and to the other things attached. A question of how bad that short first in what's taken out first - the fixture and it's plug or the threefer. In any case, it's also getting close to an second if not third possibility of the threefer's failure.
Still three potential causes of it and one specific way to rule out one of them which has not been recognized yet. A second thing you might note that could cross out the second one. Given the picture however it will confound and make it more confusing yet because the neutral I had not noticed at the time is also burned up - but not the ground. Nor is the plug in any way melted down.
Only damage to the plug is in the area that holds the hot pin in place It broke in allowing the hot pin to slide backwards some. You will also probably not note but have it noted that the pin spacing on the hot pin is smashed together. This is what's necessary for a tight connection. The pin itself looks like it got heated red hot for a period of time due to discoloring. The insulation off this pin and for some reason also the neutral having this heat also flaked off.
The plug was factory installed and was of crimp type thus there is no chance of a loose set screw in crimping wire to terminal. Strain relief was tight but not too tight, and the outer jacket on the wire at the strain relief and away from it looked to be in good shape.
Any help in re-stating the observations?
JahJahwarrior
Active Member
man...i reallyuy feel stupid, first ic ant' answer very well the par question, and now this too....
but it's ok for the two sides of the pin to touch, ,right? i have seen stage pins, just not much. It sounds like the dude pushed it into a bad socket or somethig, pushing the two sides together because the hole was too small, and pushing in the pin because of some obstruction in the socket. i kow what crimping is, but i do not konw how you crimp the wire to the pin. ir eally can't think of what exactly the problem could be....is there anything really obvious that i am not noticing, or that i have touched upon but need to develpto more?? ?
but it's ok for the two sides of the pin to touch, ,right? i have seen stage pins, just not much. It sounds like the dude pushed it into a bad socket or somethig, pushing the two sides together because the hole was too small, and pushing in the pin because of some obstruction in the socket. i kow what crimping is, but i do not konw how you crimp the wire to the pin. ir eally can't think of what exactly the problem could be....is there anything really obvious that i am not noticing, or that i have touched upon but need to develpto more?? ?
Can we rule out something random like someone taking al ighter to the plug?
Plug has heat damage to wire and the plug is broke
Was plastic melted or was it cracked off?
If melted pin holder damage could be result of problem if cracked I would suggest it is the blame.
Where there any signs of damage on the outside to suggest that the problem did NOT origant inside?
Still strugling with a way to catc to see if it was too many amps, with out knowing where is was in the show some one could have abused it with a few differnt conectors.
I would chop off the broken end and bad wire and just make a new one as long as the wire is up to standerd.
Plug has heat damage to wire and the plug is broke
Was plastic melted or was it cracked off?
If melted pin holder damage could be result of problem if cracked I would suggest it is the blame.
Where there any signs of damage on the outside to suggest that the problem did NOT origant inside?
Still strugling with a way to catc to see if it was too many amps, with out knowing where is was in the show some one could have abused it with a few differnt conectors.
I would chop off the broken end and bad wire and just make a new one as long as the wire is up to standerd.
At some point I hope the pictures are posted. I’ll send them to Mayhem tonight to see if he beats Dave to the task on posting them. I was once sent a step by step set of directions for posting pictures here and it went right over my head. If I can find them, I’ll attempt again.
So far you both are doing just fine in thinking thru a problem and have at all times been right on the cusp of an answer. Perhaps not the proper technical answer or the specific cause of it much less the three possibilities for the cause, (might be four at this point) more in a related to and similar things centered around the same things one might notice, but still right on the cusp of an answer.
There was no damage or melting to the plug body itself except that the retaining part at the rear of the pin was broken - not by way of heat (probably); more from concussion such as from an un-lucky dropping of the adaptor on the pin in just such a way. Than again the pea and the princess type theory of something inside the other connector or something wrong with it is also a possibility in causing it to break and slide backwards. In this pin sliding backwards on a Bates plug - because there is different types of plug design thus it’s important, there was lots of room behind the pin for it to do so without shorting to another conductor. Shorting within this plug is not the cause given no shorts were noted where the conductors come back together at the strain relief. In looking at the conductors at the strain relief, if too tight or conductors were nicked while the wire was stripped, this could be a cause in other situations but not in this case.
Specifically in a too tight strain relief, the malleable material such as the insulation around conductors if forced out of the way - I have seen as little as 1/32" of insulation between conductors on cables carrying 20 amps and more given the rest of the insulation is forced out of the way. That strain relief holds really tight up until the insulation it’s forcing out of the way, at least the remainder of it allows the insulation to melt away in a dead short. Than it’s loose again once it’s done melting. (Always read and follow the manufacturer directions on doing a strain relief. Them little slips of paper are there for a reason, if you have not read it, perhaps you should because there is frequently details that are needed to know. Now if I could only get “professional” tech people to do so. They know what they are doing by way of making their living at doing so - “you trying to tell me my job?”) This especially becomes a problem where the wire flexes right next to the strain relief. Conductors move as the wire flexes and if the strain relief is too tight, they can cut thru what little insulation is left between conductors as the conductors move. Been there, done that on 208v plugs, not pretty.
In nicking the wires you strip, even if not all the way thru the insulation, with use and pulling on the wires, those nicks open up in exposing wires. All you need than is either moisture to bridge the gap between conductors or sufficient amperage for a short to occur. As said however, both conditions were not present. Such things were the subject of a PBS special on why some planes started falling out of the sky. In either case, it was noted that neither was the case.
The pins of these plugs a little gap or slit cut in them which serves two purposes over pins of say a Cee Form pin and sleeve plug that does not have any slits cut parallel to the length of the pin.
The purpose of this slit is two fold. As the pin gets heated up with current, it allows for expansion and contraction of the pin without adverse effects to it. Second with this slit, it allows some amount of spring to the pin both in retention in the socket, and even when hot and expanded, allowing the plug to be removed.
To maintain a proper tension plug to connector, it’s necessary for this slot to stay parallel on each of the pins that join with a socket. With use and abuse this gap in the pin frequently becomes crunched together. Ever hear about not dropping your cables “clunk” on the stage deck? Beyond possibly breaking the pin loose from it’s housing so it slides backwards within the body of the plug, or even breaks the outer shell of the plug, such dropping can cause the pins to bend or gap to squeeze together. This stepping on them etc.
These abuse issues and lot number differences between plugs of a specific date in alignment with plugs of another date; much less wee bit of differences between one brand joining with another while the slotted pin will compensate for some of it, does cause the slot in the pin to be squeezed together at times in use. No big thing take out your handy pin splitter and correct the problem. Short of re- slitting the pin, it forms a sort of cone shape in two of the three dimensions. In having a cone shape fitting into a parallel slot, naturally it’s going to have less surface contact with the other sleeve it’s connected to. This less surface contact can have a certain amount of heating effect on the pin when under load but normally not sufficient enough to cause failure. Something to watch with these male pins, but not something that’s normally going to burn down a building. The other reason to watch the gapping of a male stage pin is because of tension reasons. If the plug does not have a bit of resistance as it slides home into a female connector, it might slide out during a show, much less either it or the female connector’s gapping is in proper in causing even at times the current to jump between socket and pin which causes a lot of heat. These arcs will tend to either weld the connectors together or cause pitting from welding on the surface of the pins and sockets. Pitting is also a bad thing in removing surface area to conduct electricity.
Raised sections from the welding will tend to prevent the other than raised sections of the plug to contact the female part of it, pitts and recesses while less dire remove that amount of area from contacting the other conductor. That’s why you don’t hot patch or in other words plug in or remove a load from the power source. In doing so you tend to arc the conductors together in causing this at the first point of contact. This arc welding can prevent the surface area of a pin from contacting a sleeve with sufficient amounts of contact. (Need to test a fixture, install a switch that is designed to turn power off and on. Need to check a fixture, turn the dimmer off.)
Specific to this problem, while the male hot pin was squeezed together, there was no arcing observed on it’s surface, just a change in the color on the pin due to heating.
This heating can be because of a loose screw in holding the wire even furrled wire to the pin or sleeve/female connector. The wire without good contact to the pin it’s attached to tends to heat up in an extreme when current flows thru it at a high resistance due to the means of clamping. Never put a bare wire under a set screw, never over tighten it. In over tightning it, you cut into the conductor and by way of pressure on it or specifically those conductors most under tension by the screw, you cause a high resistance load because some of the conductors are really clamped hard together, and some are not as tight. In a loose connection, none of the conductors are really tight to the screw terminal. As above, some less than others unless in a ferrule or wrapped in holding the conductors together in a similar way.
Remember that current follows the path of least resistance. Since a wire is a path of least resistance it tends to follow it as long as it’s easy to do as if a water hose. Clamp down too tight on the hose and the water will wish to find another place to escape. Clamp down too loose on the fittings and it’s also going to escape. This escaping energy becomes heat in the form of resistance to the current flow. I have another set of pictures TBA demonstrating this in the case of a 100 amp distribution block when these conditions and others were found on a three phase 400A distro panel.
In any case, given current follows the path of least resistance, it will also tend to flow down the outer round surface of a conductor because of this. This term is the term “skin effect.” There is less resistance to current flow towards the outer parts of the conductor than in the inner parts of the conductor that’s all copper and no air as it were. Never cut down the outside of a conductor cable so it fits within a lug that’s too small otherwise to fit. When absolutely necessary to make the cable smaller, always cut the inner conductors and bend the outer conductors inwards due to this skin effect while tying in power (later).
In the case of a high tension clamping of the wire to the plug or any terminal of it, you squeeze a conductor in high resistance because of the skin effect. The current will still wish to flow to the outer edges around the pressure applied by the set screw. Some parts of the conductor will be less clamped than other parts of it especially when you don’t use a ferrule or similar means to ensure all conductors receive the same pressure. The current will naturally flow to these parts of least resistance. If the conductors are not clamped sufficiently, the individual strands both under screw terminal and strand to strand will than ac to each other in jumping the current. This arcing than causes heat which melts the conductors jumping in the current which further causes resistance in even more heat yet.
(Note: this is a very important concept to understand by way of lamps fitting into sockets or any other electrical joining of materials that other wise are individual conductors.)
Clamp the conductor too loose, and you have the same problem as above with little arcs of electricity following the path of least resistance much less any movement with the cable will tend to make a higher arcing contact point with it. Once you get back to the wire from this clamped junction, you also get back into the classic skin effect of the current traveling around a round outer surface of the wire. In going from clamp to round conductor, you get into problems mentioned above about cutting those outer strands of a feeder cable about what happens when the current has in a cable to get between the area of the clamp, less supported outer areas of a plug or even inner conductors of a cable that now have an outer layer to go to in a thinned out conductor. This even to the point of broken strands of wire tends to cause heat in the current following that path of least resistance going from say a flat section of it with the outer edges less clamped and often broken than to the outer edges of the round wire. Lots of resistance to a easy flow of current here.
Also in a turning screw clamping down on individual conductors of a stranded wire you tend to get the cutting effect on the wire that happens as the screw turns it’s way into clamping. Another reason for using a ferrule or sleeve around the stranded wires. That said, a ferrule that’s too large to clamp the conductors won’t really support them in keeping them tightly bound under the clamp, nor will the ferrule in not having bulk around it’s cylinder prevent the screw from just cutting thru it as if it were screw going into individual conductors.
For this reason, say if I’m wiring a lighting fixture that uses 16ga wire, I don’t just use the 12ga ferrule unless I double up the fixture’s 16 ga conductor to 13ga a much closer fit, because the screw in clamping down on it will just cut thru the ferrule and even use the ferrule’s sharp cut thru edges to further cut into the wire conductors. Instead I use a 16ga ferrule sized for the wire with the 12ga ferrule sleeved over it so as to provide both a larger area under the set screw for it to hit and also for more metal in using two ferrules for that set screw to tighten into. 16ga inner sleeve than bands the wire conductors so all receive about the same amount of pressure on them, the outer sleeve closer fits the opening in the hole and provides a second layer of metal between screw clamping down on it and it just cutting because there is no support under it.
Think of the use of a ferrule as similar to the mechanical advantage you might have in clamping a piece of rope to a woodworking C-Clamp. First the strands of the rope won't clamp too well to the C-Clamp in being sufficient to pull it. Next we add a soup can around the wire. This metal surround around the say 3/4" rope better clamps down on the rope, but does not really encase the rope well. Next we find a 3/4" ID can or tube to fit around the wire, but it's really thin thus cut thru easily. Given this we add something to gap between the rope encasing ferrule and the screw down clamp in adding thickness and resistance to this twisting clamping pressure.
Given these details, why does wire in plugs once they failed, often seem like the person that tightened the plug did not ensure the terminal was tight? In addition to the skin effect of current flow, remember expansion and contraction also. Might be someone was using a cordless drill or cordless screw driver to tighten the screw terminals without verifying tension by hand. Such tools reduces torque on the screw with each use due to less voltage given off by the battery no matter the clutch setting - always verify the tension by hand. Many times a clutch set cordless tool will click off but the terminal will still be loose. Beyond this and important no matter if by hand or by tool is another key factor - expansion and contraction. This especially the case both when over clamped and when used without ferrules. The conductor in explained above will get hot by way of resistance. Hot metals expand. While they expand they tend to re-settle the stacking on individual conductors in pushing them out of the way. Once those conductors expanded that were pushed out of the way of other conductors that expanded more, when cool, they tend to make for a loose connection. Re-use this connection and it’s now high resistance no matter the installation torque. This especially the case when you put bare wires into a terminal without the benefit of a ferrule to keep the wires together. Some of them conductors will be cut, some clamped so they are solid with other conductors, some short of this ferrule band will just be frayed and loose conductors.
While you do tend to want a tension device applied to wire to be sufficiently tight not to come loose, you don’t want to over tighten them or be under tight given your theory of what’s tight is different than the standard. This is also why specific torque tensions is specified on most plug instruction sheets. Something like 20 PSI for a 60 amp stage pin plug as opposed to 120 PSF for a CamLoc terminal. Given most of don’t have torque screw drivers or wrenches to be used, we and the industry in general relies upon the 1/4 turn past finger tight method in general. Given this base of finger tight is something you have to verify against a known source - someone that by way of their own training has also been verified to have the right tension. Short of this it is torque wrenches in verifying your tension or feel for what’s what PSI in tension.
Given all of this, the plug in question had a factory installed crimp pin instead of a screw terminal. More specifically, the company that manufactured the plugs onto the cable for me were using a four pin indent tool onto a plug using a smaller sized pin cavity specifically designed for the size of a 12ga wire to fit into it. This four pin indent tool costing big bucks, not only accurately crimps the terminal with the accuracy you might expect of a expensive tool, but also in crimping the wire by way of all four sides to it tends to crimp down onto the wire very benevolent to it’s skin effect. Unless the dial for wire size on the crimp tool was set for the wrong gauge of wire - up or down from 12 AWG, there is little to no chance the specific plug in question had other than the proper and low resistance crimp applied to the wire attached to it. We can thus assume in seeing a crimped terminal done by a pro company that it is the proper pressure on the wire on this plug and that it was done properly until proven otherwise.
Such crimp terminals on the stage pin plug is an alternative to the set screw and ferrule method more normal to similar plugs given you need specialized gear to crimp such things.
Hope this info gives out more info on the question and gives out more hints about the options for what went wrong, much less in general how such electricity flows down a wire. Such areas that get hot are hot indeed either by arching or just resistance in general. This heat is dissipated outward from the source of the heat. As a overt hint, this might be a key factor in tracking down the source for the heat, or as soundman says, “I would chop off the broken end and bad wire and just make a new one as long as the wire is up to standard.” Perhaps you might have found a key test as to one of the causes of the failure in better stating an observation as to what went wrong. Now it’s a question of if you note what you than would be studying and crossing out what things could not be the cause of the problem. Thus my also note of being on the cusp of the problem or rational for it's cause.
So far you both are doing just fine in thinking thru a problem and have at all times been right on the cusp of an answer. Perhaps not the proper technical answer or the specific cause of it much less the three possibilities for the cause, (might be four at this point) more in a related to and similar things centered around the same things one might notice, but still right on the cusp of an answer.
There was no damage or melting to the plug body itself except that the retaining part at the rear of the pin was broken - not by way of heat (probably); more from concussion such as from an un-lucky dropping of the adaptor on the pin in just such a way. Than again the pea and the princess type theory of something inside the other connector or something wrong with it is also a possibility in causing it to break and slide backwards. In this pin sliding backwards on a Bates plug - because there is different types of plug design thus it’s important, there was lots of room behind the pin for it to do so without shorting to another conductor. Shorting within this plug is not the cause given no shorts were noted where the conductors come back together at the strain relief. In looking at the conductors at the strain relief, if too tight or conductors were nicked while the wire was stripped, this could be a cause in other situations but not in this case.
Specifically in a too tight strain relief, the malleable material such as the insulation around conductors if forced out of the way - I have seen as little as 1/32" of insulation between conductors on cables carrying 20 amps and more given the rest of the insulation is forced out of the way. That strain relief holds really tight up until the insulation it’s forcing out of the way, at least the remainder of it allows the insulation to melt away in a dead short. Than it’s loose again once it’s done melting. (Always read and follow the manufacturer directions on doing a strain relief. Them little slips of paper are there for a reason, if you have not read it, perhaps you should because there is frequently details that are needed to know. Now if I could only get “professional” tech people to do so. They know what they are doing by way of making their living at doing so - “you trying to tell me my job?”) This especially becomes a problem where the wire flexes right next to the strain relief. Conductors move as the wire flexes and if the strain relief is too tight, they can cut thru what little insulation is left between conductors as the conductors move. Been there, done that on 208v plugs, not pretty.
In nicking the wires you strip, even if not all the way thru the insulation, with use and pulling on the wires, those nicks open up in exposing wires. All you need than is either moisture to bridge the gap between conductors or sufficient amperage for a short to occur. As said however, both conditions were not present. Such things were the subject of a PBS special on why some planes started falling out of the sky. In either case, it was noted that neither was the case.
The pins of these plugs a little gap or slit cut in them which serves two purposes over pins of say a Cee Form pin and sleeve plug that does not have any slits cut parallel to the length of the pin.
The purpose of this slit is two fold. As the pin gets heated up with current, it allows for expansion and contraction of the pin without adverse effects to it. Second with this slit, it allows some amount of spring to the pin both in retention in the socket, and even when hot and expanded, allowing the plug to be removed.
To maintain a proper tension plug to connector, it’s necessary for this slot to stay parallel on each of the pins that join with a socket. With use and abuse this gap in the pin frequently becomes crunched together. Ever hear about not dropping your cables “clunk” on the stage deck? Beyond possibly breaking the pin loose from it’s housing so it slides backwards within the body of the plug, or even breaks the outer shell of the plug, such dropping can cause the pins to bend or gap to squeeze together. This stepping on them etc.
These abuse issues and lot number differences between plugs of a specific date in alignment with plugs of another date; much less wee bit of differences between one brand joining with another while the slotted pin will compensate for some of it, does cause the slot in the pin to be squeezed together at times in use. No big thing take out your handy pin splitter and correct the problem. Short of re- slitting the pin, it forms a sort of cone shape in two of the three dimensions. In having a cone shape fitting into a parallel slot, naturally it’s going to have less surface contact with the other sleeve it’s connected to. This less surface contact can have a certain amount of heating effect on the pin when under load but normally not sufficient enough to cause failure. Something to watch with these male pins, but not something that’s normally going to burn down a building. The other reason to watch the gapping of a male stage pin is because of tension reasons. If the plug does not have a bit of resistance as it slides home into a female connector, it might slide out during a show, much less either it or the female connector’s gapping is in proper in causing even at times the current to jump between socket and pin which causes a lot of heat. These arcs will tend to either weld the connectors together or cause pitting from welding on the surface of the pins and sockets. Pitting is also a bad thing in removing surface area to conduct electricity.
Raised sections from the welding will tend to prevent the other than raised sections of the plug to contact the female part of it, pitts and recesses while less dire remove that amount of area from contacting the other conductor. That’s why you don’t hot patch or in other words plug in or remove a load from the power source. In doing so you tend to arc the conductors together in causing this at the first point of contact. This arc welding can prevent the surface area of a pin from contacting a sleeve with sufficient amounts of contact. (Need to test a fixture, install a switch that is designed to turn power off and on. Need to check a fixture, turn the dimmer off.)
Specific to this problem, while the male hot pin was squeezed together, there was no arcing observed on it’s surface, just a change in the color on the pin due to heating.
This heating can be because of a loose screw in holding the wire even furrled wire to the pin or sleeve/female connector. The wire without good contact to the pin it’s attached to tends to heat up in an extreme when current flows thru it at a high resistance due to the means of clamping. Never put a bare wire under a set screw, never over tighten it. In over tightning it, you cut into the conductor and by way of pressure on it or specifically those conductors most under tension by the screw, you cause a high resistance load because some of the conductors are really clamped hard together, and some are not as tight. In a loose connection, none of the conductors are really tight to the screw terminal. As above, some less than others unless in a ferrule or wrapped in holding the conductors together in a similar way.
Remember that current follows the path of least resistance. Since a wire is a path of least resistance it tends to follow it as long as it’s easy to do as if a water hose. Clamp down too tight on the hose and the water will wish to find another place to escape. Clamp down too loose on the fittings and it’s also going to escape. This escaping energy becomes heat in the form of resistance to the current flow. I have another set of pictures TBA demonstrating this in the case of a 100 amp distribution block when these conditions and others were found on a three phase 400A distro panel.
In any case, given current follows the path of least resistance, it will also tend to flow down the outer round surface of a conductor because of this. This term is the term “skin effect.” There is less resistance to current flow towards the outer parts of the conductor than in the inner parts of the conductor that’s all copper and no air as it were. Never cut down the outside of a conductor cable so it fits within a lug that’s too small otherwise to fit. When absolutely necessary to make the cable smaller, always cut the inner conductors and bend the outer conductors inwards due to this skin effect while tying in power (later).
In the case of a high tension clamping of the wire to the plug or any terminal of it, you squeeze a conductor in high resistance because of the skin effect. The current will still wish to flow to the outer edges around the pressure applied by the set screw. Some parts of the conductor will be less clamped than other parts of it especially when you don’t use a ferrule or similar means to ensure all conductors receive the same pressure. The current will naturally flow to these parts of least resistance. If the conductors are not clamped sufficiently, the individual strands both under screw terminal and strand to strand will than ac to each other in jumping the current. This arcing than causes heat which melts the conductors jumping in the current which further causes resistance in even more heat yet.
(Note: this is a very important concept to understand by way of lamps fitting into sockets or any other electrical joining of materials that other wise are individual conductors.)
Clamp the conductor too loose, and you have the same problem as above with little arcs of electricity following the path of least resistance much less any movement with the cable will tend to make a higher arcing contact point with it. Once you get back to the wire from this clamped junction, you also get back into the classic skin effect of the current traveling around a round outer surface of the wire. In going from clamp to round conductor, you get into problems mentioned above about cutting those outer strands of a feeder cable about what happens when the current has in a cable to get between the area of the clamp, less supported outer areas of a plug or even inner conductors of a cable that now have an outer layer to go to in a thinned out conductor. This even to the point of broken strands of wire tends to cause heat in the current following that path of least resistance going from say a flat section of it with the outer edges less clamped and often broken than to the outer edges of the round wire. Lots of resistance to a easy flow of current here.
Also in a turning screw clamping down on individual conductors of a stranded wire you tend to get the cutting effect on the wire that happens as the screw turns it’s way into clamping. Another reason for using a ferrule or sleeve around the stranded wires. That said, a ferrule that’s too large to clamp the conductors won’t really support them in keeping them tightly bound under the clamp, nor will the ferrule in not having bulk around it’s cylinder prevent the screw from just cutting thru it as if it were screw going into individual conductors.
For this reason, say if I’m wiring a lighting fixture that uses 16ga wire, I don’t just use the 12ga ferrule unless I double up the fixture’s 16 ga conductor to 13ga a much closer fit, because the screw in clamping down on it will just cut thru the ferrule and even use the ferrule’s sharp cut thru edges to further cut into the wire conductors. Instead I use a 16ga ferrule sized for the wire with the 12ga ferrule sleeved over it so as to provide both a larger area under the set screw for it to hit and also for more metal in using two ferrules for that set screw to tighten into. 16ga inner sleeve than bands the wire conductors so all receive about the same amount of pressure on them, the outer sleeve closer fits the opening in the hole and provides a second layer of metal between screw clamping down on it and it just cutting because there is no support under it.
Think of the use of a ferrule as similar to the mechanical advantage you might have in clamping a piece of rope to a woodworking C-Clamp. First the strands of the rope won't clamp too well to the C-Clamp in being sufficient to pull it. Next we add a soup can around the wire. This metal surround around the say 3/4" rope better clamps down on the rope, but does not really encase the rope well. Next we find a 3/4" ID can or tube to fit around the wire, but it's really thin thus cut thru easily. Given this we add something to gap between the rope encasing ferrule and the screw down clamp in adding thickness and resistance to this twisting clamping pressure.
Given these details, why does wire in plugs once they failed, often seem like the person that tightened the plug did not ensure the terminal was tight? In addition to the skin effect of current flow, remember expansion and contraction also. Might be someone was using a cordless drill or cordless screw driver to tighten the screw terminals without verifying tension by hand. Such tools reduces torque on the screw with each use due to less voltage given off by the battery no matter the clutch setting - always verify the tension by hand. Many times a clutch set cordless tool will click off but the terminal will still be loose. Beyond this and important no matter if by hand or by tool is another key factor - expansion and contraction. This especially the case both when over clamped and when used without ferrules. The conductor in explained above will get hot by way of resistance. Hot metals expand. While they expand they tend to re-settle the stacking on individual conductors in pushing them out of the way. Once those conductors expanded that were pushed out of the way of other conductors that expanded more, when cool, they tend to make for a loose connection. Re-use this connection and it’s now high resistance no matter the installation torque. This especially the case when you put bare wires into a terminal without the benefit of a ferrule to keep the wires together. Some of them conductors will be cut, some clamped so they are solid with other conductors, some short of this ferrule band will just be frayed and loose conductors.
While you do tend to want a tension device applied to wire to be sufficiently tight not to come loose, you don’t want to over tighten them or be under tight given your theory of what’s tight is different than the standard. This is also why specific torque tensions is specified on most plug instruction sheets. Something like 20 PSI for a 60 amp stage pin plug as opposed to 120 PSF for a CamLoc terminal. Given most of don’t have torque screw drivers or wrenches to be used, we and the industry in general relies upon the 1/4 turn past finger tight method in general. Given this base of finger tight is something you have to verify against a known source - someone that by way of their own training has also been verified to have the right tension. Short of this it is torque wrenches in verifying your tension or feel for what’s what PSI in tension.
Given all of this, the plug in question had a factory installed crimp pin instead of a screw terminal. More specifically, the company that manufactured the plugs onto the cable for me were using a four pin indent tool onto a plug using a smaller sized pin cavity specifically designed for the size of a 12ga wire to fit into it. This four pin indent tool costing big bucks, not only accurately crimps the terminal with the accuracy you might expect of a expensive tool, but also in crimping the wire by way of all four sides to it tends to crimp down onto the wire very benevolent to it’s skin effect. Unless the dial for wire size on the crimp tool was set for the wrong gauge of wire - up or down from 12 AWG, there is little to no chance the specific plug in question had other than the proper and low resistance crimp applied to the wire attached to it. We can thus assume in seeing a crimped terminal done by a pro company that it is the proper pressure on the wire on this plug and that it was done properly until proven otherwise.
Such crimp terminals on the stage pin plug is an alternative to the set screw and ferrule method more normal to similar plugs given you need specialized gear to crimp such things.
Hope this info gives out more info on the question and gives out more hints about the options for what went wrong, much less in general how such electricity flows down a wire. Such areas that get hot are hot indeed either by arching or just resistance in general. This heat is dissipated outward from the source of the heat. As a overt hint, this might be a key factor in tracking down the source for the heat, or as soundman says, “I would chop off the broken end and bad wire and just make a new one as long as the wire is up to standard.” Perhaps you might have found a key test as to one of the causes of the failure in better stating an observation as to what went wrong. Now it’s a question of if you note what you than would be studying and crossing out what things could not be the cause of the problem. Thus my also note of being on the cusp of the problem or rational for it's cause.
Mayhem my buddie from down under that also talks funny, he is my bud.
In any case, as mentioned later in me noting it, this also melted neutral conductor but not the ground conductor noted later when taking photos disturbs and throws off all the simple three causes left for even me based upon only a hot conductor melting.
There is a fourth and fith perhaps option now that even I have not figured out for sure given this now. For even me, the like melted neutral adds a new factor that even I can't at this point explain as one of three factors.
In any case, as mentioned later in me noting it, this also melted neutral conductor but not the ground conductor noted later when taking photos disturbs and throws off all the simple three causes left for even me based upon only a hot conductor melting.
There is a fourth and fith perhaps option now that even I have not figured out for sure given this now. For even me, the like melted neutral adds a new factor that even I can't at this point explain as one of three factors.
wow, that was defanatly a ship post!
I still dont think I understand the entire situation well enough to have any kind of idea what is going on (not that it's ship's fault, I am much more of a show me it, let me feel it, kind of guy). I am probably restating ship's hints, but what I can gather is that there has probably been arcing between some parts of the plug. Could this have been arcing between the ground pin and the hot pin that is damaged? (I seem to remember something from way back that the ground pin was one of the pins with damage) If the plug was dropped, or jammed the wrong way, it seems to me that the pins and wireing inside could be jostled enough, that if some small arcing had melted abit of the insulation already, arcing between two of the pins could have taken place. Again, I really have no idea if I am on the right path here or not, but hey, I might as well share what I am thinking!
Ship, you left me with another question after reading your last post (well, probably several, but I'll just ask one for now b/c it's on the top of my head) what is a ferrule? Maybe it's something I know, but just dont know the real name for, or maybe I am not familar with it. Could someone discribe it or post a pic? Thanks!
I still dont think I understand the entire situation well enough to have any kind of idea what is going on (not that it's ship's fault, I am much more of a show me it, let me feel it, kind of guy). I am probably restating ship's hints, but what I can gather is that there has probably been arcing between some parts of the plug. Could this have been arcing between the ground pin and the hot pin that is damaged? (I seem to remember something from way back that the ground pin was one of the pins with damage) If the plug was dropped, or jammed the wrong way, it seems to me that the pins and wireing inside could be jostled enough, that if some small arcing had melted abit of the insulation already, arcing between two of the pins could have taken place. Again, I really have no idea if I am on the right path here or not, but hey, I might as well share what I am thinking!
Ship, you left me with another question after reading your last post (well, probably several, but I'll just ask one for now b/c it's on the top of my head) what is a ferrule? Maybe it's something I know, but just dont know the real name for, or maybe I am not familar with it. Could someone discribe it or post a pic? Thanks!
A ferrule is a nickel plated copper surround for the wire that is sized to the wire size in encapsulating it and providing a cyllinder of metal between it and the individual conductors beneath it and the screw terminal twisting into individual conductors.
McMaster Carr or Allied Elecronics in using the key word ferrule might provode the best results in a cadd cam picture of such a thing. In McMastercarr.com look say for part number 9681k22 for an insulated version of it I most use with a 12ga of the same length sleeve over it for lighting fixture wiring. You gonna like McMaster Carr as a supplier over time this given freqent double orders to them on a busy work day for me such as today in getting parts. First order this morning arrived before 3PM direct delivery, second order in having faxed to them after noon will come UPS by 12 PM the next day. Gotta love for me while I have it at lest same day delivery and most frequent stuff in stock thus no matter the sales adds by other vendors, or how much cheaper at times, just ensuring that you get the product is worth the extra price.
McMaster Carr or Allied Elecronics in using the key word ferrule might provode the best results in a cadd cam picture of such a thing. In McMastercarr.com look say for part number 9681k22 for an insulated version of it I most use with a 12ga of the same length sleeve over it for lighting fixture wiring. You gonna like McMaster Carr as a supplier over time this given freqent double orders to them on a busy work day for me such as today in getting parts. First order this morning arrived before 3PM direct delivery, second order in having faxed to them after noon will come UPS by 12 PM the next day. Gotta love for me while I have it at lest same day delivery and most frequent stuff in stock thus no matter the sales adds by other vendors, or how much cheaper at times, just ensuring that you get the product is worth the extra price.
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