Feeder cable gauge question - ground vs. hots & neutral

[gafftapegreenia]

Forgive me if this has been discussed before, so here goes:

A few weeks ago their was a photo shoot in the main space here on campus. Professional local film people were hired to do the job. Part of what they did was tie in directly to our company switch so they could use their own distribution equipment to power the 6K spacelights w/ 60 amp Bates connectors that they brought in. (It was quite a weekend, we ended up dumping 54K of pure white light on to a 16'x16' space, quite a different world for someone who had done primarily theatre, such as myself)

So heres the question. When they tied in their feeder, the hots and neutrals were all 2/0, but the ground was #2. Is this allowable practice? For some reason I thought this was frowned upon? I'm only ever been used to seeing a five wire feeder system where all 5 cables are of the same gauge. I should also add that these five cables had been loomed, and looked like they had been for a long time. (not that that is bad persay, but it does derate the conductors, which always has to be considered)


On a related note regarding cam-lock orientation: Their distro had males for the hots and neutral, and a female for ground, instead of all five being males, or the hots males with neutral and ground being females. Another variant in the mix.

 

[Footer]

First, never consider what film guys do as standard practice. This is the industry that uses vice grips with cam connections after all.

But yes, an undersized ground is totally kosher. Its not usually done in the theatre world because we don't haul feeder like the film guys do, but it can be done. I can not remember the formula off the top of my head at 1am.... Steveterry will probably chime in on this one...

 

[derekleffew]

... So heres the question. When they tied in their feeder, the hots and neutrals were all 2/0, but the ground was #2. Is this allowable practice? For some reason I thought this was frowned upon? ...

See 2011 NEC 250.122 for EGC sizing.
.

 

[MisterTim]

On a related note regarding cam-lock orientation: Their distro had males for the hots and neutral, and a female for ground, instead of all five being males, or the hots males with neutral and ground being females. Another variant in the mix.

I don't know how common this is, but it's also totally kosher. It's to prevent accidental swapping of ground with a hot wire, same as having both ground and neutral swapped. They're just slightly different standards; I've seen them all. Ours are ground and neutral swapped.

 

[gafftapegreenia]

I don't know how common this is, but it's also totally kosher. It's to prevent accidental swapping of ground with a hot wire, same as having both ground and neutral swapped. They're just slightly different standards; I've seen them all. Ours are ground and neutral swapped.

Oh I know it's totally kosher - just had to mention it as we recently had the discussion about which way the feeder cams go

 

[derekleffew]

I don't know how common this is, ...

Reversing-only-the-ground is a very distant third, besting only last place finisher reversing-only-the-neutral in the feeder gender wars. http://www.controlbooth.com/forums/lighting-electrics/20237-cam-lok-gender-orientation.html

 

[epimetheus]

See 2011 NEC 250.122 for EGC sizing.

To further Derek's reference for those who don't have a copy of the NEC handy, the EGC is sized based on the rating on the upstream overcurrent protective device. In the case of a #2 copper EGC, the upstream overcurrent device would have a maximum rating of 500A (based on NEC Table 250.122).

 

[STEVETERRY]

To further Derek's reference for those who don't have a copy of the NEC handy, the EGC is sized based on the rating on the upstream overcurrent protective device. In the case of a #2 copper EGC, the upstream overcurrent device would have a maximum rating of 500A (based on NEC Table 250.122).

Right you are.

And don't forget that NEC section 520.53(H)(2) prohibits a single conductor grounding cable smaller than #6AWG, no matter what the rating of the overcurrent protective device.

ST

 

[meatpopsicle]

Right you are.

And don't forget that NEC section 520.53(H)(2) prohibits a single conductor grounding cable smaller than #6AWG, no matter what the rating of the overcurrent protective device.

ST

@STEVETERRY - people in the local still talk about your zip cord ground demonstrations at P.A.

@Footer - Those guys with the vice grip tie ins were film guys...but we still frown on that practice.

 

[derekleffew]

... NEC section 520.53(H)(2) ...

520.53(H)(2), which references 250.122, is actually more on point to the original question than my answer in post #3.

To further Derek's reference for those who don't have a copy of the NEC handy, ...

1. WHY would anyone NOT have a copy handy?
2. NFPA 70 may be viewed free (with registration) at http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70 . (I swear they keep hiding/changing the link, in an attempt to persuade people to just buy the dang thing.)

 

[STEVETERRY]

@STEVETERRY - people in the local still talk about your zip cord ground demonstrations at P.A.

Clearly, my class and the grounding demo must have had the desired effect, if they still remember it! Perhaps it was the smell of burning PVC or the hot glow of #18AWG copper on fire that printed it on their memories!

Cheers

ST

 

[mstaylor]

Just curious, what did you do?

 

[Edrick]

As stated the film industry does everything different than most of the other industries. It's one of the only one I know that can get away with the crazy concoctions they put together for grip, lighting, effects and get away with it. It's always amazed me that you have so many people in the industry working with the power distribution hacking things together yet don't really have a clue what they're dealing with. The loomed cable you see is very very common (at least on all the sets I've worked on) the 5 wire one you saw is sometimes known as a 5-Wire-Banded. But every areas got their own terminology. I was amazed when I went from the theater to film then back to help out in theater how small the 20A bates looked afterwards.

Take a look at ARRI Lighting and Mole Richardson, two of the most popular lighting suppliers for film and Mole does a lot of the distribution. Lunch Boxes, Snack Boxes, Distribution, etc...

 

[STEVETERRY]

Just curious, what did you do?

5kW fresnel, 50A branch circuit, #18AWG zip cord grounding conductor to the dimmer rack, 50A ground fault. Burning insulation and grounding conductor.

Moral of the story: use a grounding conductor of the right size, or it won't protect you.

ST

 

[jstandfast]

5kW fresnel, 50A branch circuit, #18AWG zip cord grounding conductor to the dimmer rack, 50A ground fault. Burning insulation and grounding conductor.

Moral of the story: use a grounding conductor of the right size, or it won't protect you.

ST

I remember Jeff Turner telling me about that one @ the time. Still sounds instructive.

 

[reggie98]

First, never consider what film guys do as standard practice. This is the industry that uses vice grips with cam connections after all.

Cut me a break, the clamp is a Trico (test clamp) and used for temporary tie-ins to "house power" on location. Not used all that often and easier than installing lugs in someone else's panel.

 

[STEVETERRY]

Cut me a break, the clamp is a Trico (test clamp) and used for temporary tie-ins to "house power" on location. Not used all that often and easier than installing lugs in someone else's panel.

Following this line of thinking, let's go back to using Tweco welding connectors, because they're easier to assemble than Cam-Loks.

My point: safety is an evolving standard. Twecos were once considered acceptable for 120/208 feeders, because there was nothing else available. Now they are considered unsafe, which they surely are in that application.

Trico clamps, while "easier", also fall into that unsafe category. They have no NRTL certification, and have undergone no testing for the application you describe. They have no current rating, only a wire gauge specification.The fact that they are easier does not make them remotely safe.

Trico clamps have a "notionally insulated" handle of who knows what voltage or dielectric rating, which invites live tie-ins, a bad thing.

I've done lots of tie-ins with Trico clamps. At the time, did I understand anything about arc-flash hazards? Nope. If I did, the Trico clamps would have been in the garbage, and I would have been looking for the main breaker to shut it off and lock it out before doing the tie-in with proper lugs. Safety also evolves with knowledge. The more ignorant one is of the risks, the safer things seem.

Last week, I was walking by a location film shoot at Lincoln Center in New York. It was pissing down rain. There was a 5-wire 2/0 feeder set running in the gutter, with water flowing over it. At one point in the set, there was a set of Cam-Lok tees in line, with the open contacts of the tees facing skyward and collecting water. The set was live. there was no barrier to protect the public or crew from this hazard.

No knock on you, the poster, but I often wonder why such unsafe practices are tolerated in the film industry by the crews that are placed at risk. "I've done it many times without a problem" is not a good answer.


Just my 2 cents.

ST

 

[Dionysus]

I have to completely agree with SteveTerry, way too many unsafe practices are tolerated way too much still with electricity. Especially after getting my arc-flash training I realize more about just how stupid some of the things I've seen done (or have done myself) were. How many times I've done live tie-ins, with no arc-flash gear, or tools rated for it either. Then again there are times I've gone in to fix/diagnose main services where arc-flash gear would of done no good anyways lol.

There is a reason that there is a whole section in the CEC for grounding, and other rules besides. And very specific guidelines on neutral/identified conductors.

Even more scary is there is one company I know of who will not work with me or hire me because they know I will not tolerate some of their vastly-below-code practices. I've threatened to call the Electrical Safety Authority on them actually. And I really should.

 

[reggie98]

No knock on you, the poster, but I often wonder why such unsafe practices are tolerated in the film industry by the crews that are placed at risk. "I've done it many times without a problem" is not a good answer.


Just my 2 cents.

ST

"I've done it many times without a problem" is not my answer either, nor is doing live tie-ins.
Why are unsafe practices observed on some film/video location shoots? Because bad habits/practices are being passed from more senior crew members (who were taught incorrectly or not at all) to those more junior. Electrical safety is really the realm of the Gaffer and his wishes and instructions on a non-union shoot are sometimes ignored. "I don't care, I just want to get this shot", says the DP, AD, Director, Producer, etc.
Do you think that the film schools, even the major ones are teaching the fundamentals of generators and power distribution? They are not. Can you learn it all from reading the Harry Box book? No again. Standard practice is to raise all cam connections up on wood, rain or not, wrap camloks with plastic if it's raining and cover Distro boxes with plastic, cover the unused port on a "T" with tape. Is it always done? No, for a litany of bad reasons.