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Author Topic: Power Install  (Read 4213 times)

Aleks.Barbour

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Power Install
« on: May 30, 2004, 12:02:29 am »

The theater where I work recently had an electrician upgrade our power drop so that we could end up with two dedicated 110v 20A circuits for our house PA system, and a 220v 30A 4 prong drop.  We have a breakout box that we can attach for visiting sound companies that has 6 20A 110v circuits, each on different poles (but the same phase - I don't really understand this bu6t I am off to research it - and I'm not the one doing the work).

We are in the process of running new circuits from those 2 20A circuits, one to the amp rack (just one amp now with no major upgrades planned for the near or distant future), and the other will run to the booth where it will power the booth (audio equipment only).  

If we need to power back line, we'll hook in the breakout box and do it from there.

My question is twofold:
1) Does it matter if the amps are on a different leg of the power than the rest of the audio system (not really sure how pole affects amps when the power supplies are charging the rails thousands of times a second), and
2)for back line should we stick to hooking into the circuits on the breakout that match the leg of the audio gear, the amps, or does it not matter?

The box we are working from has a dedicated 220v, 60a feed and nothing in it besides these three circuits. Is there a preferred/ideal combination of circuits that we should shoot for? With the panel open and the wiring of the runs just starting getting changes made is easiest now.  
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Hal Bissinger/COMSYSTEC

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Re: Power Install
« Reply #1 on: June 01, 2004, 05:41:57 pm »

Well, first off and if I understand you correctly, that "breakout box" that plugs into the 220v/30Amp circuit IS NOT LEGAL unless it incorporates 20amp circuit breakers with the 20 amp receptacles in the box at the end AND the cable is of sufficient size (at least 10AWG)to handle 30 amps. Reason being that the outlets (and probably the cable) are rated at 20 amps and you are plugging this into a 30 amp receptacle. I'm also confused by how you can have 6 receptacles on the same phase but each on different "poles". Hopefully I'm wrong and this "breakout box" is factory assembled and UL listed and by "poles" he means breakers as I described.

This can be a serious matter nowadays, anything that is or can be construed as a violation is going to cost the club or theater owners big if there is a problem. The electrician can also be held liable criminally and civilly so he better get his act together.

As to your question about if there will be a problem if the amps are put on a different circuit and/or phase (not pole) than the rest of the equipment- no, shouldn't matter. What will though is the grounds and without seeing the installation it would be difficult to comment.

-Hal

Aleks.Barbour

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Re: Power Install
« Reply #2 on: June 01, 2004, 06:10:17 pm »

Thanks for the reply - I'll add clarification:

Each of the 6 20A circuits has its own circuit breaker, 3 on one leg and 3 on the other.  The box also has a proper tail, and has been seen, inspected, and signed off on by the fire inspector.

Working from memory, we used to have a breaker box that had two hots, a neutral, and a ground coming into it (does this imply 2 phases then?), with a fuse on each of the hots, and a rating of 220v, 60A.  The only output off of this box was the 4 prong outlet (again with a proper tail).  Recently, we had an electrician add in a box between the outlet and the breaker.  The new box has one 30A 220v circuit, and 2 20A 110v circuits.

Based on how this seems to work, the new box has a limit of 6 20A 110v circuits, but the breakout box can only provide full capacity to three of those at any given time.  So, we should pull three of the breakers out of the breakout box and limit that to 3 20A circuits, with two on one rail and one on the other. We should then add the 6th circuit into the new breaker box and mount a permanant 20A 110 outlet to the wall (for backline - the position is good for powering on-stage devices).

That leaves us with a 30A 220v outlet and a 20A 110v outlet for visiting companies which seems decent based on experience.

As an aside, this whole box is for audio power only, and is clean back to the main service entry to the building.
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Hal Bissinger/COMSYSTEC

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Re: Power Install
« Reply #3 on: June 01, 2004, 08:43:57 pm »

The box... has been seen, inspected, and signed off on by the fire inspector.

Usually it is the electrical inspector who has the qualifications and authority to inspect electrical work unless the fire inspector also doubles as the electrical inspector where you are.

...we used to have a breaker box that had two hots, a neutral, and a ground coming into it (does this imply 2 phases then?)

Could if the service is 3 phase but since you have 240v it is probably single phase 120/240. These would just be referred to as "the hot legs".

[A box] with a fuse on each of the hots, and a rating of 220v, 60A.

Since you mention fuses, does this box have a handle on the side to turn it off? If so it's a disconnect, the capacity would be determined by the size of the fuses installed which would in turn be determined by the wire size, either case no more than 60A if that's what it says on the label.

...but the breakout box can only provide full capacity to three of those at any given time.

Yes, 30A is a small but that is 30A per leg. You can have two 20A breakers on each leg for a total of four. It's doubtful that you will load each to capacity but if you do the 30A breaker back in the panel will trip.

So, we should pull three of the breakers out of the breakout box...

Pull two out and put another circuit in the panel as you suggest. Keep in mind that everything in this case can add up to more than 60A per leg. The worst that will happen is that a 60A fuse will blow and then you will know it's time to upgrade.

Aleks.Barbour

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Re: Power Install
« Reply #4 on: June 01, 2004, 08:59:52 pm »

Again, thank you.

We do have a 3 phase supply into the building but I do not know how this panel is connected.

For the inspectors I am not sure which saw it (I've never had to deal with one directly) but based on the electrician that installed it, the code books that we have referenced, and the inspectors that have seen it we are in good shape, and ensuring that our venue is safe is the top priority. (As an aside - when introducing visiting companies, especially kids, to our stage which is very cramped we point out the two areas taped out in yellow, the fly rail and the electrical service panel, and introduce them as the yellow zones of death - if you cross those lines without the explicit permission of the TD or me we're gonna just have to get rid of you.) Smile

As for upgrading - this is the last upgrade.  The service panel is full and we have been told we get no more from the local power company. Luckily, we make really ineffieient use of our wiring so we drive it at nowhere near capacity currently.  This last upgrade gets the audio system onto it's own circuit and now we can start tracing out some of the older wiring and planning to have it all cleaned up.
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