What happens when you assume

[porkchop]

So back in August my boss decided that a 1200W Clay Paky Alpha Wash pulls 1200/208 = ~6A, divided over two phases means ~3A per leg. We had some 30A 3Ø 277/480V connectors laying around so he had cables made with these connectors to run 4 lights using the female 30A as the beginning of a big ole' 4 fer. The way it was wired was (arbitrarily naming the phases) unit 1 and 2 powered by phases X and Y and units 3 and 4 powered by Y and Z. That should work right, no problem well under rating. Well the reality is these lights pull almost 10A per leg so that means that the draw is 20A on phase X, 40 on Phase Y, 20 on Phase Z, not to mention the angry neutral because of the unbalanced phases. So yah, not good.

Fast forward to now in February, the two 30A connectors haven't been unplugged since the cables where built, the cables are picked up and put down every week as one. The lights are on for between 20 and 60 hours a week, every week. Yah I'm pretty sure the only reason this worked for this long is the fact the connectors where fused together. Today (after load in and three shows this week) the 4 lights won't turn on, I go up and look at the connectors in question, when I find it impossible to take the connectors apart I know we're in trouble. I go and unplug the distro end, come back, and have to BEAT THE CONNECTORS AGAINST THE TRUSS to get them to come apart. These are the results, I would have taken a picture of the rest of the female connector but the rest of it turned into dust as soon as I got the connectors apart.

 

[Footer]

I can't believe that no one could smell that when they were dressing the cable on the in or out. Usually that burnt plastic smell lingers days or even weeks after its burnt. I hate that smell.

 

[cprted]

I can't believe that no one could smell that when they were dressing the cable on the in or out. Usually that burnt plastic smell lingers days or even weeks after its burnt. I hate that smell.

That's the first place my mind went too. How could you not smell that thing smouldering away?

 

[Footer]

When your in a 20,000 seat arena that exchanges air every 10 minutes and your truss is 30' off deck, I does not suprise me no one smelled it when it was in operation.

 

[porkchop]

Yup 40' trim, 5k seats is a small venue for us, and we have a good bit of smoke producing pyro so the air exchangers are on pretty high. This isn't a cable I run, but I've walked by it every week since august and never got a hint of that odor that I sadly know oh too well.

 

[cprted]

Yup 40' trim, 5k seats is a small venue for us, and we have a good bit of smoke producing pyro so the air exchangers are on pretty high. This isn't a cable I run, but I've walked by it every week since august and never got a hint of that odor that I sadly know oh too well.

Well, that's what I get for assuming ... totally missed this was an arena show ... carry on ...

 

[soundman]

Not to nitpick but I bet the neutral didn't even notice the unbalanced load because with most 208V lights the neutral isn't used.

 

[porkchop]

Sorry angry ground, the wire that would have been the neutral on unit is used for the second leg. That's how Clay Paky made it. None the less three phase power is supposed to be balanced and it most certainly wasn't.

 

[gcpsoundlight]

that is scary. we had an incedent where some extention leads were hanging next to some 1k parcans, and the socket fused onto the light! they were hired too.

 

[Chris15]

Whilst still not compliant, had these *lovely" adapters been wired for 3 fixtures in an XY, YZ, ZX configuration, they would have probably survived. Compliance would require breakers...

I hope that it was a MALE that formed the start of this contraption, else we need to really go back to Electrics 101.

Remember that in phase to phase loading, the neutral is not even connected and so you have the same current down each leg of the load. So there was a fundamental flaw in your boss's sums. 6A per leg per fixture... If you've got 20A on each load, then the load on phase Y won't be 40A because o the phase shifting, but it will a fair proportion of that. (I'll do the sums if someone cares enough).

Ground should also have not cared in this config, unless something shorted and it was dumping the fault current. So it really would just be the Y conductor that's really unhappy.

Folks, unless you have the insurance coverage for it, don't go making funky adapters. And if you do have the insurance for it, then chances are you also will have or have access to the know how to make it safe... I've built adapters that were perfectly safe IN THEIR SPECIFIC APPLICATION but would never be approved and were destroyed after that particular job...

 

[zmb]

Based on the looks of the connectors, I'm surprised those didn't catch fire.