Another twist to this.

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I work in TV/Movie world. When we wire duplex receptacles on stage-built sets, we use your normal 120v duplex receptacles.
We break the L-N tabs and use two 20A circuits to feed the receptacle.
The top half of the receptacle is controlled by a dimmer. (Panel A) 800A
The bottom half of the receptacle is controlled by floor power (Panel B) 800A

One outlet fed from two circuits that come from different panels (usually, very far away from each other)
I've asked the qualified electricians in the studios if this is safe and no one will confirm (yes/no) It's either one or the other?
Can anyone please enlighten me?

Thanks
 

packersparky

Senior Member
Location
Wisconsin
Occupation
Inspector
I work in TV/Movie world. When we wire duplex receptacles on stage-built sets, we use your normal 120v duplex receptacles.
We break the L-N tabs and use two 20A circuits to feed the receptacle.
The top half of the receptacle is controlled by a dimmer. (Panel A) 800A
The bottom half of the receptacle is controlled by floor power (Panel B) 800A

One outlet fed from two circuits that come from different panels (usually, very far away from each other)
I've asked the qualified electricians in the studios if this is safe and no one will confirm (yes/no) It's either one or the other?
Can anyone please enlighten me?

Thanks

Not compliant in my opinion. Multiple branch circuits on the same yoke must simultaneously disconnect. See NEC 210.7.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
Is it safe? Probably. It's a restricted area; the only people to touch the wiring will be familiar with your local practice and aware that two breakers need to be turned off and locked out before it's deenergized.

Is it National Electrical Code-compliant? Probably not.

Does it need to be NEC-compliant? I'm not sure. Either "qualified personnel only" or "temporary wiring" exemptions might apply.

Article 530 of the NEC addresses Motion-Picture and Television Studios, but I don't think there's anything in there that addresses this question.
free online access: https://www.nfpa.org/codes-and-stan...des-and-standards/detail?code=70&tab=research
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The only thing you can really do to minimize danger would be to make sure both halves of each duplex are fed by the same phase, so there is no phase-to-phase voltage difference between the two hots.
 

ron

Senior Member
The top half of the receptacle is controlled by a dimmer. (Panel A) 800A
The bottom half of the receptacle is controlled by floor power (Panel B) 800A

NEC 2017 404.14(E) does not permit a dimmer to be connected to a receptacle. So it is also not code compliant in that respect as well as NEC 210.7 for common disconnect
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
NEC 2017 404.14(E) does not permit a dimmer to be connected to a receptacle. So it is also not code compliant in that respect as well as NEC 210.7 for common disconnect

I work in the Entertainment industry, and I can tell you this is common practice. It's often a necessity, as onstage lamps (practicals) must be controlled with the rest of the stage lighting. The bottom half of the receptacle is then used to operate other stage practicals that require constant power (record player, stereo, etc...)

Is it safe? Yes. Is it to code? Technically no, but it really doesn't matter. It's not permanently installed, and it's accessible only to trained, qualified stage electricians and stagehands that understand what's going on. We typically wire out of the outlet box with two 6' SO cable whips. The dimmed half of the receptacle is connected to the whip with a 20A stage pin plug, and the non-dim side is connected to an L5-20 Twist-Lok plug (prevented inadvertent swapping of dimmed and non-dimmed power to the receptacle). The local plugs serve as the "local disconnecting means" if you need to service the receptacle.

Everything backstage is connected with SO cable, so it's not "code" anyway. That's just the way it is in the Entertainment industry. No one is running conduit on a set that is only up for a few weeks.

I used to live and work in Chicago - possibly the most stringent jurisdiction in the country when it comes to electrical and fire safety in theater (for obvious reasons). The Fire Marshal was perfectly fine with "temporary" wiring methods, so long as things like wire gauge and grounding were up to snuff. The NEC can't always account for strange occurrences, and I can tell you that Entertainment can be the strangest of animals; it's amazing what designers will dream up.



SceneryDriver
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
The only thing you can really do to minimize danger would be to make sure both halves of each duplex are fed by the same phase ...
That would prevent 240 volts from appearing at the receptacle, (which I don't think is a violation or an inherent hazard) but wouldn't change the problem of two different breakers in two different panels needing to be turned off and locked out before the receptacle is completely deenergized.

At the cost of completely rewiring your sound stage, you could make this code-compliant by using a residential 120/240 panel, feeding one phase with floor power and the other from the dimmer, using a two-pole/one-handle breaker for each receptacle and feeding each receptacle with a single 4-wire cable.

You could reduce the hazard with a notation at each receptacle identifying the circuits and panels feeding it.
 
stage wiring

stage wiring

Thank you and everyone else on this board for your input on this situation.

Scenery Driver explained the way that sets are rigged in a lot more detail than I did.
My main concern about this method was the fact that:
Example: Top of receptacle (panel A, blue phase) controlled by dimmer board.
Bottom half of receptacle (panel B, red phase) controlled by circuit breaker.
Now, we have an antique two wire table lamp plugged into the top of receptacle. (a prop for part of the scene)
In the bottom half of the receptacle, we have a "studio light" (often, we need more light for filming)
These two lights are sometimes in very close proximity to each other; within arms reach.
If there happened to be a fault in either of these fixtures and someone was touching both units at the same time, would that be... a bad day?
Also: a couple of replies mentioned; ...must be on the same phase. Another: must be on a different phase.
Which one is correct?
We now use a lot of LED studio lights combined with our existing incandescent lights and every now and then, we have a some power problems (flickering lights and malfunctions) a couple of times when they were plugged into a set wall outlet.
We then test them on floor power and the units are fine?

Thanks for your time.









I work in the Entertainment industry, and I can tell you this is common practice. It's often a necessity, as onstage lamps (practicals) must be controlled with the rest of the stage lighting. The bottom half of the receptacle is then used to operate other stage practicals that require constant power (record player, stereo, etc...)

Is it safe? Yes. Is it to code? Technically no, but it really doesn't matter. It's not permanently installed, and it's accessible only to trained, qualified stage electricians and stagehands that understand what's going on. We typically wire out of the outlet box with two 6' SO cable whips. The dimmed half of the receptacle is connected to the whip with a 20A stage pin plug, and the non-dim side is connected to an L5-20 Twist-Lok plug (prevented inadvertent swapping of dimmed and non-dimmed power to the receptacle). The local plugs serve as the "local disconnecting means" if you need to service the receptacle.

Everything backstage is connected with SO cable, so it's not "code" anyway. That's just the way it is in the Entertainment industry. No one is running conduit on a set that is only up for a few weeks.

I used to live and work in Chicago - possibly the most stringent jurisdiction in the country when it comes to electrical and fire safety in theater (for obvious reasons). The Fire Marshal was perfectly fine with "temporary" wiring methods, so long as things like wire gauge and grounding were up to snuff. The NEC can't always account for strange occurrences, and I can tell you that Entertainment can be the strangest of animals; it's amazing what designers will dream up.



SceneryDriver
 

MAC702

Senior Member
Location
Clark County, NV
Yet another thread that I never remember what it's about until I hover or click on it. Can we PLEASE use the actual subjects in the subject line?

The stage world is a different world. I hope the NEC doesn't apply (or has the big exception) or these guys would never get their job done. They have their own rules and things are not usually haphazard. Things that are rushed are done by guys with some serious skills.

That said, we do need to make sure things are done safely. But NEC "safely?" No. I've no problem with the STANDARD being discussed in the OP. But I better not see that somewhere else.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
I work in the Entertainment industry, and I can tell you this is common practice. It's often a necessity, as onstage lamps (practicals) must be controlled with the rest of the stage lighting. The bottom half of the receptacle is then used to operate other stage practicals that require constant power (record player, stereo, etc...)

SceneryDriver

As others have said, there is nothing wrong with split wiring a duplex, and there is nothing wrong with switching half the receptacle off by some means.

The code compliance issues are not that hard to fix: either feed the switched and un-switched from the same panel, or run them to separate duplexes.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Also: a couple of replies mentioned; ...must be on the same phase. Another: must be on a different phase.
Which one is correct?
I suggested same phase for less hazard while energized, not when de-energizing.

Different phase is only necessary when supplying two loads with a shared neutral.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Enough responders have already said it isn't compliant with NEC requirements. I will take one such requirement and expand on it. There are devices that could burn themselves up or even start a fire, if you fed them with too low a voltage. You really don't want to plug such an item into an outlet that is controlled by a dimmer. To prevent an inadvertent use of a dimmer on a device that can't tolerate it, the code requires that the outlet itself not be the standard type we all see in our homes and offices. It has to be a receptacle (with matching plug) that is unique (i.e., nothing like anything else used in the area). You will clearly reply that you don't need to worry bout that, because you only use that outlet for a light fixture. And as long as that remains true, you shouldn't have an issue.

But is the installation you describe "safe"? Well, let's think about that. Suppose you turned all burners of your electric range on high, and left them on day and night. Would that be "safe"? I suppose that if you don't touch the range top with your hand, and if the cat doesn't try to walk over the range top, and if you don't have any combustible materials too close to the range top, then nothing bad should happen. You could define "safe" as meaning nothing bad will happen unless and until someone does something stupid (or careless). But the engineers and electricians who participate in this forum have a professional obligation to protect the public against their own stupidity (or carelessness), at least to the extent that the NEC has requirements intended to establish that protection.

So you won't get a blessing from me. I don't like the installation you described, and I don't think it is safe. You may counter with the length of time (and the number of times) you have used it, all without incident. I counter back by asking you to perform a mental exercise (really - don't do this for real!). Consider that at the beginning of each work day you start your car, put on blinders and sound-proof ear protection. You wait a random amount of time, then suddenly back your car into the street. Suppose you have done that ten days in a row without incident. Would you conclude that the practice has been proven to be "safe"? Would you need to do it more times without incident to prove it is safe?

In summary,
"An accident that is waiting for a place to happen will, given time, find that place." (Famous saying by some famous person)
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Even if the OP's description is the norm for theatrical scenarios OSHA wouldn't care.

Roger
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Thank you and everyone else on this board for your input on this situation.

Scenery Driver explained the way that sets are rigged in a lot more detail than I did.
My main concern about this method was the fact that:
Example: Top of receptacle (panel A, blue phase) controlled by dimmer board.
Bottom half of receptacle (panel B, red phase) controlled by circuit breaker.
Now, we have an antique two wire table lamp plugged into the top of receptacle. (a prop for part of the scene)
In the bottom half of the receptacle, we have a "studio light" (often, we need more light for filming)
These two lights are sometimes in very close proximity to each other; within arms reach.
If there happened to be a fault in either of these fixtures and someone was touching both units at the same time, would that be... a bad day?
Also: a couple of replies mentioned; ...must be on the same phase. Another: must be on a different phase.
Which one is correct?
We now use a lot of LED studio lights combined with our existing incandescent lights and every now and then, we have a some power problems (flickering lights and malfunctions) a couple of times when they were plugged into a set wall outlet.
We then test them on floor power and the units are fine?

Thanks for your time.

Short answer: nothing "bad" would happen to you, any worse than touching any other not-properly-grounded devices. That's why you make sure everything is properly grounded (or double-insulated), but that goes for everything. The ground wires for both sources are obviously tied together, and to the ground terminal on the receptacle. The green wire provides the return path for fault current. If you have an "antique" floor lamp you want to use and its wiring is suspect, re-wire that lamp. It'll shock someone whether it's used in your living room or on stage if the wiring is dodgy.

If you're plugging your LED lighting fixtures into dimmed power, I'm not surprised you're having issues with them flickering. They use switchmode power supplies, and use DMX-controlled PWM to control the apparent intensity of the LEDs in the fixture. Your fixtures will flicker/blink when connected to dimmed power, if the chopped up AC waveform can't supply a high enough average voltage to the power supply input. Depending on the quality of the power supply, it might end up damaged. Don't connect devices that shouldn't be dimmed to dimmed power.

The one caveat to the above statement is that you can use "dimmed" power to supply non-dom loads, if you park the dimmer at full and simply use it as another circuit. I've found it preferable to do that at the dimmer rack, instead of relying on the light board to keep a channel at full; programmers can fat-finger the light board and do dumb things.


SceneryDriver
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I'm pretty sure there are some issues that are not code compliant in the way these things are wired.

I also suspect if anyone really cared they could get some kind of dispensation from the AHJ given how much money is involved in making TV shows and movies.
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
And I forgot to add:
This is really a completely immaterial discussion. Since this receptacle - mounted in the wall of the set - is cord and plug connected, it is utilization equipment and isn't governed by the NEC at all. It's really nothing more than a fancy extension cord. The NEC stops at the actual receptacle for the dimmer and/or non-dim circuit.

< dead horse beaten />

SceneryDriver
 
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