Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Nicholas Radina]

Hello everyone!

I know this may be an elementary question.

I'm trying to work out the safest method of providing power to a local venues amp rack and backline stringers.

The venue has 4 dedicated 20a breakers for the amp rack and stringers.

Looking at the specs for the various amps, I see the a/c power requirements.

The issue I have is only 4 20a circuits available for amp and band power.

The amps are:
9 QSC mx1500a (drawing 10A each)
2 PLX 3002 (12A) - Monitor Amps

I'm assuming that the power requirement spec is based on the MAXIMUM current draw.

Taking into account the band power, how best should I tackle this beast to insure not tripping a breaker.

Thanks for any help and I'm sorry for the elementary question.

Nicholas

[Mike Pyle]

You need to look at the work the amps are doing, not just the input current spec. An amp that is bridged and powering subs is typically going to draw a lot more a/c than an amp running stereo into HF drivers or mids. You might be able to run just one or two sub amps on a circuit, while powering several HF amps from another.

[Tim Weaver]

It seems pretty easy to me. You need one circuit for the band. The other three will be available for your power amps. Spread the load evenly and hope for the best. Thats really all you can do, until you run dedicated power to the amp rack.....

[TJ (Tom) Cornish]

You will have the potential for tripped breakers with your arrangement no matter how you spread them around.  As others have said, identify the amps that are working the hardest and put fewer of them on one circuit than the lighter-run amps.

Truly guaranteeing that you won't trip breakers will mean that either you limit the system's output to not exceed the available input current, or adding more circuits.

[jason misterka]

Nicholas -

I know from direct experience the you can not put more than 3 RMX 850s on one 20amp without tripping, even if not on sub duty. I think the RMX line replaced the MX, whatever that is worth.  It's not a direct correlation to your amps I know, but some of the lower cost amps have a higher power draw even when idle.

You can usually put multiple (3 or 4) PLX amps on one circuit, though sub vs HF does make a difference.  As does 2ohm vs 4ohm speaker loads, in my understanding when running the amp at 2ohms your current draw is significantly greater.

So it depends on you setup.  But I don't think you have enough AC any way you look at it.  You may get lucky but you are running a risk.

Good Luck,
Jason

[jeff harrell]

as one who worked as a commercial journeyman electrician i can tell you the circut breaker is designed to protect the wire. a 20 amp circut breaker will trip(if not defective) at a tad over 20 amps. what i did is take about a 2 foot lenght of #10 THHN stranded black,white,green wire and put a 15 amp cord ends on them. i plugged the little cord in the wall and plugged the cord going to ONE amp in and took my $90.00 greenlee clamp on amp meter and measured the amps going through the black wire with the amp flashing the clip light while playing a few different cd's with deep powerful kicking bass and thats the amp requirement for that model amp. idi the same with the other amps. playing at clip is the most amps the amp will draw. you also need to use xtension cords rated the same. if you dont drive your amps wide open they will draw less amps. an amp putting out 50 watts will draw less amps then when it putting out 300 watts. 2-step amps will draw even lower amps until they are turned up and the high current rails take over. someimes its better to rent a small generator(propane if possible) and set it out back and run equipment off that if the house panel is tapped out. you can also measure all you equipment with a clamp on amp meter and then label it and put stuff together that adds up to just under 20 amps.

[TJ (Tom) Cornish]

jeff harrell wrote on Wed, 19 January 2011 00:16

as one who worked as a commercial journeyman electrician i can tell you the circut breaker is designed to protect the wire. a 20 amp circut breaker will trip(if not defective) at a tad over 20 amps.

This is not axiomatic - thermal breakers are affected by manufacturing tolerances, ambient temperature of the breaker panel, and any connection resistance present at the breaker. 80% loading is a safer number.

jeff harrell wrote on Wed, 19 January 2011 00:16

what i did is take about a 2 foot lenght of #10 THHN stranded black,white,green wire and put a 15 amp cord ends on them. i plugged the little cord in the wall and plugged the cord going to ONE amp in and took my $90.00 greenlee clamp on amp meter and measured the amps going through the black wire with the amp flashing the clip light while playing a few different cd's with deep powerful kicking bass and thats the amp requirement for that model amp. idi the same with the other amps. playing at clip is the most amps the amp will draw. you also need to use xtension cords rated the same. if you dont drive your amps wide open they will draw less amps. an amp putting out 50 watts will draw less amps then when it putting out 300 watts. 2-step amps will draw even lower amps until they are turned up and the high current rails take over. someimes its better to rent a small generator(propane if possible) and set it out back and run equipment off that if the house panel is tapped out. you can also measure all you equipment with a clamp on amp meter and then label it and put stuff together that adds up to just under 20 amps.

This is a useful test, but clamp meters are notorious for having slow integration time.  They're great for measuring lighting loads, less so for dynamic loads like power amps.

The OP hasn't told us what the amps do - are they part of a large speaker cluster?  Montior amps?  All on sub duty?  That's a lot of amplifiers on not a lot of power - assuming they're run fairly hard.  If on the other hand they are used for a distributed audio system where the quantity of amps are needed for different audio content (delay speakers, etc.) and aren't run hard, then things may be just fine.

I think if it were me, I might try to put at least an amp or two on the stage circuit.  This is less than ideal, but so is blowing breakers.  The better solution is more circuits, of course.

[Joe Brugnoni]

Quote:

I think if it were me, I might try to put at least an amp or two on the stage circuit. This is less than ideal, but so is blowing breakers. The better solution is more circuits, of course.

I agree with this as he has said he has a couple for stage monitors, band equipment does not draw very much in a normal 4 or 5 piece band and If it was me I would put the monitor amps or at least one on with the band circuit.

Quote:

I'm trying to work out the safest method of providing power to a local venues amp rack and backline stringers. The venue has 4 dedicated 20a breakers for the amp rack and stringers.

Are you going to provide the rig, or help with the power upgrade??


If it is the power your working on,  and you have the budget, install a panel for the stage only and the amp rack and place them all on there own circuits, 200 amps is pretty big panel but it would insure you have plenty.

what about lights?

[Dan Johnson]

jason misterka wrote on Tue, 18 January 2011 22:33

I know from direct experience the you can not put more than 3 RMX 850s on one 20amp without tripping, even if not on sub duty.

Really?  I can't tell you how many times I've run 2 RMX2450s and 2 Yamaha P5000s all off a 15 amp rack power unit with no problems.  4 ohm load on every channel with subs running off the 2450s and running the system pretty hard.  If I put anything else on the rack power unit it will trip it.  I recently added an RMX850 plugged into the same 20 amp circuit that the rack power unit is running off of with no issues.

[jason misterka]

Yeah - I had to have a 7th circuit run for a club install because of it.  Some of our QSC PL racks can run four amps without concern but my understanding is that the smaller output lower cost amplifiers use a different kind of power supply that has a fairly high idle draw.  I don't have time to look it up now but you may...

Gotta run,
Jason

[ProSoundWeb Community]