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Author Topic: Power problem?  (Read 10738 times)

Thomas Lamb

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Power problem?
« on: May 11, 2014, 12:23:19 pm »

So I'm pretty sure we have a power issue. However, I can't track it down so I solicit the help of those much wiser than I.

Here's the deal. We have four almost identical systems from gear to power distribution. They are all portable (it's portable churches) so they are all at different locations. This one is at a movie theatre. Here's the layout. Each location has 3 phase 120/208 power and we have had 30 amp breakers installed with L21/30 connections. It runs about 100' on 8/5soow to a stinger BREAKERED breakout (L21/30 in and thru) that feeds lights off of 2 legs and FOH off the other (GLD and ETC smartfade). From there it feeds through the breakout downstage to the rack with a racpac in it
L21/30 in. That racpac feeds a NEXO NX4x4, IEM's, wireless, and computers.

Last week I got a emergency call that the amp had an error (error PS CH 2 2 V) pulled the amp took it back to the shop (thought then maybe we had a issue on a leg but it metered good) put it on the bench same error. Power supply? Probably so sent it out for repair and sent out a brand new one (BRAND NEW!) got a call this morning they kicked the amp on and it immediately let the smoke out! Not happy. Went out metered everything each leg 119-121 to neutral and to ground 208 phase to phase 0v ground to neutral. 3 weeks ago they lost the power supply to the lightng console it runs off the same leg as the audio console no problem with it though. Back around Christmas we lost a keyboard a few months before that we lost the power supply to the wireless distro. Every time something happens we always go back meter everything and nothing stands out. So... Where do I go from here? FYI there are projectors that the theatre owns running out of the same panel.

HELP!!

PS.
Never had a issue like this at any other campus (same systems).
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bigTlamb

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Brian Jojade

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Re: Power problem?
« Reply #1 on: May 11, 2014, 01:18:51 pm »

My first guess would be that you have a loose neutral connection somewhere.  When you're metering with no load, it looks just dandy fine.  However, when you put a load on it, the connection somewhere starts to arc and disconnect.  When this happens, if you've got an unbalanced load on the 3 phase system, you're going to see voltage swings, with the lowest load devices getting the highest voltage across them.

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TJ (Tom) Cornish

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Re: Power problem?
« Reply #2 on: May 11, 2014, 01:23:31 pm »

My first guess would be that you have a loose neutral connection somewhere.  When you're metering with no load, it looks just dandy fine.  However, when you put a load on it, the connection somewhere starts to arc and disconnect.  When this happens, if you've got an unbalanced load on the 3 phase system, you're going to see voltage swings, with the lowest load devices getting the highest voltage across them.
yep. Get some large par lamps or heaters and see what the voltage does under load.
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Raul Suarez

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Re: Power problem?
« Reply #3 on: May 11, 2014, 04:47:03 pm »

Is it possible that the lights on just 2 legs are making the load unbalanced, and drawing down the neutral, thus causing the 3rd leg with a lighter load to go very high?  You don't say what the draw of your lighting system is.

Raul Suarez
Third Ear Sound
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Matthew Knischewsky

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Re: Power problem?
« Reply #4 on: May 11, 2014, 05:17:59 pm »

I agree with the others. Load down the power with heaters or par cans or whatever you have that can be used as a constant load - I've used heat guns, coffee makers... and then meter the power and see what's happening. If you load down one leg the other legs should remain close to the same (nominally 120V). The danger of a loose neutral is that it turns the power distribution system into a series circuit instead of a parallel circuit and produces the kinds of failures you're seeing.

Having the lights on 2 circuits shouldn't cause problems if everything is working normally. Best practice would be to load all phases as evenly as possible but it's not a big deal on a 30 amp circuit.

I'd open up all your cables and distribution boxes and tighten the connections as a matter of course. At the same time inspect all of the connections and make sure the wire is being clamped down on and not the insulation, and a general inspection that all is as it should be. Standard disclaimer, always do this work un-energized.

Matt

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Mike Sokol

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Re: Power problem?
« Reply #5 on: May 11, 2014, 06:49:09 pm »

Yup, sounds like a loose or undersized neutral somewhere. I once did a gig at an old mill where my 50 KW of PAR lights (25 KW per leg) could cause the neutral to go high by 10 volts or more on the opposite leg. So if we bumped all the lights on one phase, anything on the other unloaded leg would see over 130+ volts. Many older buildings with 3-phase power regularly undersized the neutral feeding the service panel since 3-phase motor loads never draw any neutral current. But throw some power amps and lights on that same 3-phase circuit, and you'll see the neutral dragging up and down which could be reflecting into the other legs.

This probably has nothing to do with your own distro wiring, but is a PoCo and building problem. However, don't expect them to find this out for you. 

So as others have suggested, meter an unloaded leg of your distro then throw as much steady-state load as you can get on another leg. If its voltage jumps up by more than a few volts, then you've got a problem with the neutral being undersized or loose. Also be aware that if you're using tungsten lights that they draw a huge current spike when cold, typically several times (or more) of the steady state amperage draw. So if you're doing flashing tungsten lighting on one leg, then you could be dragging the neutral around on that leg by dozens of volts, and possibly spiking the H-N voltage on the other two legs by 10 or 20 volts or even more. That could be what's killing your gear.

If you could set up your lighting and get a digital storage scope on one of the unloaded legs, I'll bet you could figure this out rather quickly. 
« Last Edit: May 11, 2014, 06:53:10 pm by Mike Sokol »
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Mike Sokol
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Thomas Lamb

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Re: Power problem?
« Reply #6 on: May 11, 2014, 07:48:47 pm »

Guys thank for the help so far. The lighting load is moderate 2 source4 eliosodals with 750 watt bulbs in them per leg (x2).

So are we saying the problem may not be in my gear? I'm pulling that rig and will go through all the power distros this week. I can definately load test the phases independently and together. We have brought in portable power before and are considering doing it again until we get this figured out.

Thanks again guys.
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bigTlamb

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Mike Sokol

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Re: Power problem?
« Reply #7 on: May 11, 2014, 08:13:51 pm »

Guys thank for the help so far. The lighting load is moderate 2 source4 eliosodals with 750 watt bulbs in them per leg (x2).

So are we saying the problem may not be in my gear? I'm pulling that rig and will go through all the power distros this week. I can definately load test the phases independently and together. We have brought in portable power before and are considering doing it again until we get this figured out.

Thanks again guys.

I could certainly be in the PoCo feed between the power transformers on the street to your service panel. But it would be prudent to go through all your power distros and check for loose screws or anything goofy on the neutral connections.

Also, others on this forum can speak to this better than me, but you should get a look at the 3-phase transformers feeding your building. If there's not 3 transformers identical in size, then there could some variation of standard 3-phase Wye power. Also, get an electrician to open up your service panel and see how big the neutral is sized. If it's smaller than the three hot legs, that could be an issue with your single-phase loads. Don't do this yourself unless you're a qualified electrician or engineer as that's a good way to get yourself killed.

Just how old is this building and the power feeding it? That will give us a hint as where else to look.
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Mike Sokol
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Thomas Lamb

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Re: Power problem?
« Reply #8 on: May 11, 2014, 10:11:48 pm »

Biulding is maybe 6-8 yrs old. It is 120/208v wye. 16 theaters all digital projection. We run out of the same panel as some of the projectors each projector I presume are 208. However they have racks of QSC CX series amps 120v. Each projector has it's own sub panel mounted in the base of the projector stand.
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bigTlamb

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Matthew Knischewsky

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Re: Power problem?
« Reply #9 on: May 11, 2014, 11:07:29 pm »

Biulding is maybe 6-8 yrs old. It is 120/208v wye. 16 theaters all digital projection. We run out of the same panel as some of the projectors each projector I presume are 208. However they have racks of QSC CX series amps 120v. Each projector has it's own sub panel mounted in the base of the projector stand.

Did you ask anyone at the theatre if they're been experiencing any unexplained failures of equipment in the projection booth?
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ProSoundWeb Community

Re: Power problem?
« Reply #9 on: May 11, 2014, 11:07:29 pm »


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