Melting Twistlocks

[BenjaminD]

My highschool auditorium hasn't been maintained in a while, and we have a bunch of twistlock sockets (on pigtails) melted to the plugs in them. Have any of you encountered this problem before?
Why does this happen? Is this just a case of Abused 20 Year Old High School Auditorium Syndrome, or is it something I can prevent?
What is the best way to fix this (I have been using a hammer and destroying the connectors too damaged to open).
Ben

[Jezza]

If you don't actually "twist and lock" the connector, you can inadvertently create an arc between the barely connected pins inside the connector which will melt the connector.

Also, if you overload the connector over 20A, your breakers should trip, but if for some reason they don't, the connector might be the next place to release the energy.

I wouldn't be taking a hammer to the connectors. Just doesn't sound like a good idea. I would attempt to unscrew the twist and lock from the cable if possible and remove it that way, or cut the pigtail and put on a new connector. Unless your fixtures are twist and lock as well, put on female stage pin connectors on and make your life easier.

[soundman]

Something is very wrong if the plugs have melted together. It could be casued by several things not limited to pulling more amps through them then they are rated for or a loose conection that has caused some arcing. If it were my space I would pull the dimmers for the affected circuts and cut the pig tails. If there was enough heat to melt the plastic plugs there is a fair chance that the insulation is shot. Replacing the pig tails completly would be best.

[soundlight]

I had some of those at my HS. They were on the sockets that I was running 1800W through, and I think that (even though the cable and connectors were rated for above what I was pumping through them) there was some sort of short inside the connector due to lousy wiring that melted the plastic.

[BenjaminD]

Jezza: The connectors are too badly melted to unscrew. That's part of the problem. The socket and plug are melted together, and they're both melted enough that I can't undo them without a hammer. I have no idea if they were locked, originally... they were probably hung over 10-15 years ago (there is enough dust on the fixtures to grow a small garden. I'm cleaning them... slowly....

Everything in my theatre is twistlock. I wish we had stagepin, but we just... don't.

soundman: Due to the fuses on the dimmer (never blowing) vs the rating of the plugs, I don't think they could draw enough power to melt the connector. Actually, it might be a loose connection... except that I've found 6 connections melted together. It's possible that a previous TD didn't understand the concept of twistlock, but unlikely.

I'm scared/worried about this because it creates sparks (like when you hot-plug a fixture, except they don't go away. I caught one doing it today, I noticed the fixture behaving erratically, and went down to check it out, and discovered the connector was buzzing and occasionally sparking. And the screws holding the connector together were slightly charged(!). I flipped out, of course, (and replaced the plug and socket) but what if I hadn't noticed?

And how on earth can you replace a pigtail without removing the entire electric/batten assembly?!

soundlight: most of these channels are for striplights, not loaded over a KW... Again, I'm not sure of the intelligence of previous electricians/TD's/random people that would install plugs

[icewolf08]

It sounds to me like what you need to do is check every plug on every fixture and every plug-in strip/raceway. Make sure that all of the wiring is attached securely and correctly to each connector, and replace any that have any signs of damage (chips, cracks, charring, scorches, etc.). This could turn out to be a costly and time consuming project, but it will be totally worth it, not to mention that it is a safety issue.

[rmarston]

Been using twist locks forever - no problems. Souinds to me like an impedance problem in the connect / plug - that is if they are not being loaded beyond their rating. I bet there is loose connections on one or both sides of the connection - resulting in meltdown.

[Charc]

Edit:

Read Ship's post, next page.

[icewolf08]

Twist lock connectors are not unsafe (when installed correctly). The Key-Out twist lock connectors (I always forget the code numbers) are not supported under the NEC as I understand it, but the Key-In connectors are NEC compliant. I wouldn't quote me on this, but I believe that is true. There are still many theatre that use both kinds of twist lock connectors, and there is no reason to change everything to stage pin if you can fix/replace parts with the same connectors.

ADDITION:
Key-IN Twist Lock: L5-20 is NEMA compliant. below is a photo of one from altman:


Key-OUT Twist Lock: non NEMA compliant. below is a photo from altman:

[Edrick]

Being that your theater isn't anchient but it isn't brand new what is some of the equiptment you have for lighting and sound? Being that I'm the first person to go through the first year at our new high school I can only wonder how it will be 20+ years from now.