Splitting 3-phase circuits for 3 high draw theater fixtures.

Marshall Kidd · Apr 5, 2018

Hello.

I'm new here so my apologies if this post ended up in the wrong forum.

I have a basic understanding of phases and voltage and the lot. Today I'm trying to wrap my head around how I might be able to split one 3-phase 240v 50a source to accommodate 3 high draw theater fixtures.

Here's what I know about each of the 3 fixtures that may be useful:
-Rated at 1700VA.
-Accepts a 240v 15a plug (twist-lock, HOT, HOT, GND.)
-1200w bulb.
-Amperage test shows 12a across both phases.
-The furthest fixture from the source would be 70' one way.

My question is how to power all 3 of these fixtures of of the 240v 50a source? If so, how would you do it safely?

Thank you for your help.

Adam W · Apr 5, 2018

Would I be correct in thinking you're in America?

As I understand it you deal with multi phase differently over there - you would probably wire these lights the same way as you would a tumble dryer or air conditioner.

Ordinarily theatrical lights would be dimmed, so you'd need a suitable dimmer. This might even 'split' your supply for you - probably something a bit like this: http://www.theatrecrafts.com/archive/documents/act3datasheet.pdf

Richard Burns · Apr 5, 2018

Again not totally conversant with US 3 phase but in theory connecting them equally between phases should ensure similar loading on each cable.
So light 1 on A and B phase, light 2 on B and C phase, light 3 on A and C phase.
It would also be useful to know if there were other loads on this supply so that you can accommodate these in the calculations.

Marshall Kidd · Apr 5, 2018

Adam W said:
Would I be correct in thinking you're in America?

As I understand it you deal with multi phase differently over there - you would probably wire these lights the same way as you would a tumble dryer or air conditioner.

Ordinarily theatrical lights would be dimmed, so you'd need a suitable dimmer. This might even 'split' your supply for you - probably something a bit like this: http://www.theatrecrafts.com/archive/documents/act3datasheet.pdf

I made a mistake when I said 3-phase. What I meant was 2-phase (American) along with a neutral (that is ommited) and ground obviously.

Luckily these fixtures are locally dimmed so there is no need for a dimming power supply.

Thank you for your suggestion.

Richard Burns said:
Again not totally conversant with US 3 phase but in theory connecting them equally between phases should ensure similar loading on each cable.
So light 1 on A and B phase, light 2 on B and C phase, light 3 on A and C phase.
It would also be useful to know if there were other loads on this supply so that you can accommodate these in the calculations.

Luckily these 3 fixtures will be the only devices on this supply.

Thank you for your help.

Marshall Kidd · Apr 5, 2018

Marshall Kidd said:
Hello.

I'm new here so my apologies if this post ended up in the wrong forum.

I have a basic understanding of phases and voltage and the lot. Today I'm trying to wrap my head around how I might be able to split one 3-phase 240v 50a source to accommodate 3 high draw theater fixtures.

Here's what I know about each of the 3 fixtures that may be useful:
-Rated at 1700VA.
-Accepts a 240v 15a plug (twist-lock, HOT, HOT, GND.)
-1200w bulb.
-Amperage test shows 12a across both phases.
-The furthest fixture from the source would be 70' one way.

My question is how to power all 3 of these fixtures of of the 240v 50a source? If so, how would you do it safely?

Thank you for your help.

EDIT: 2-Phase not 3-Phase.

Richard Burns · Apr 5, 2018

S0 you have a 50A supply and a maximum 36A total load, so just connect them to the supply with appropriate protective devices and you are done.

Marshall Kidd · Apr 5, 2018

Richard Burns said:
S0 you have a 50A supply and a maximum 36A total load, so just connect them to the supply with appropriate protective devices and you are done.

Thank you for your answer.

My question is how to safely split the 240v 50 amp supply between the three fixtures, perhaps by hooking them up in parallel?

Darkwood · Apr 5, 2018

Hi @Marshall Kidd, welcome to the forum.

Can we establish firstly and given your age here, if this is theory or practical advice you are requesting?
I cannot personally comment on USA regulations or practices as we are a UK regulation based forum and your reg's are not my area of expertise, someone of your age (17) should not be undertaking any work like this unsupervised by a competent person, I would suggest you ask them your query on this matter as they will be familiar with both your regulations and the install itself.
If this is theory or coursework then we advice you seek such advise off your tutor as we do not give coursework answers out all though we are willing to nudge you in the correct direction if you can show your calculations and/or understanding on the matter.

Adam W · Apr 5, 2018

In the UK we wouldn't have an issue with wiring multiple 230v sockets onto the same circuit, however those big plugs we use which other countries laugh at are individually fused, so whatever the circuit is rated at (usually 20A or 32A) the most you can continuously draw is 13A.
In this instance if you've got enough space in the distribution board (panel) I'd probably wire them as 3 separate circuits, protected by an MCB appropriate to the size of the cable (probably 10A or thereabouts).

This said it would need to be done in accordance with NEC which I know nothing about, and may need to be done by a state registered electrician.

Marshall Kidd · Apr 5, 2018

Adam W said:
In the UK we wouldn't have an issue with wiring multiple 230v sockets onto the same circuit, however those big plugs we use which other countries laugh at are individually fused, so whatever the circuit is rated at (usually 20A or 32A) the most you can continuously draw is 13A.
In this instance if you've got enough space in the distribution board (panel) I'd probably wire them as 3 separate circuits, protected by an MCB appropriate to the size of the cable (probably 10A or thereabouts).

This said it would need to be done in accordance with NEC which I know nothing about, and may need to be done by a state registered electrician.

Thank you for your reply.

Unfortunately we cannot spare any room in this current fuse box due to some poor management (ugh) and the next closest one is about 100ft away. This one circuit is all that we have to work with.

If I understand what your saying correctly, would running a 50a circuit to a smaller box (closer to the fixtures) with 3 individual 240v 15a breakers (one for each fixture) make sense?

Thanks.

Adam W · Apr 5, 2018

You could do it that way, at least by UK standards.

Marshall Kidd · Apr 5, 2018

darkwood said:
Hi @Marshall Kidd, welcome to the forum.

Can we establish firstly and given your age here, if this is theory or practical advice you are requesting?
I cannot personally comment on USA regulations or practices as we are a UK regulation based forum and your reg's are not my area of expertise, someone of your age (17) should not be undertaking any work like this unsupervised by a competent person, I would suggest you ask them your query on this matter as they will be familiar with both your regulations and the install itself.
If this is theory or coursework then we advice you seek such advise off your tutor as we do not give coursework answers out all though we are willing to nudge you in the correct direction if you can show your calculations and/or understanding on the matter.

Hello. Apologies for not clarifying this earlier.

I will not be the one installing or organizing any of this. The risk is not worth it.

What I am trying to do is get in touch with the buildings (qualified) electrician to sort out when he would be able to put this system in.

I'd figured I'd come here and ask some experts to get a better idea of what we would like done exactly.

Thank you for your concern.

Marshall Kidd · Apr 5, 2018

Adam W said:
You could do it that way, at least by UK standards.

Great. Thank you for the advice!

Richard Burns · Apr 5, 2018

I think from a UK perspective there are the two methods indicated by AdamW. I believe loads are generally more separated in the US than the UK, so would tend toward the three circuits approach.
However it would be important to check your local codes to ensure you are complying with them.

[ElectriciansForums.net] Splitting 3-phase circuits for 3 high draw theater fixtures.

Marshall Kidd · Apr 5, 2018

Richard Burns said:
I think from a UK perspective there are the two methods indicated by AdamW. I believe loads are generally more separated in the US than the UK, so would tend toward the three circuits approach.
However it would be important to check your local codes to ensure you are complying with them.
View attachment 41667

Thank you for the advice. I will bring it up with the electrician installing the circuit(s.)

Is there a benefit in one over the other?

Splitting 3-phase circuits for 3 high draw theater fixtures.

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