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[david burns]

I'm wanting to know what size power cable I should use, i'm running bridged RMX2450 on my subs and bridged RMX1450 on my tops. I'm from the uk and here we have 230v/13a power supplies. I only had a 6-gang 13a trailing extension which only had 1.25mm (16awg )power cable, and each amplifier only had 1.25mm (16awg) IEC powerr cables so all four amplifiers and even my Dbx Driverack were running off a single 230v/13a electrical circuit. It sounded damn good though.

But I was wondering if I connected both RMX1450 amps to a 2-gang extension and ran it off one electrical circuit and then ran both RMX2450 amps, each off their own circuits, used 2.5mm (13awg) power cable for all amplifier IEC power cables and 4mm (11awg) power cable on the 2-gang trailing socket which the RMX1450 amps would be connected to, would I maybe be able to get more spl, basically because each amplifier would have more power available instead of them all sharing the power off one circuit?

[Mike Christy]

Quickly looking at the QSC specs, if you are driving 4 ohms loads from each bridged amp, then that can be close to 26A on a US 120V service, or 13A on a 240V service for dynamic music, un clipped, so in that regard you are close to the max on that circuit.

The only reason you would get more SPL is that you will be driving the amps harder, not because of the size of the AC power cord. But powering the amps from two circuits will most likely help if you do exceed the breaker limit on that single circuit.

In the US the standard is 12AWG wire for 20A, 120V at 50 feet, the longer the run, the larger the pipe needs to be to reduce voltage drops due to resistance.

Hope this helps, and that I did not mis-guide,

Mike

[david burns]

Ah right, so I won't get any higher spl out my system, it's just running my system with such small cable over such long runs only meant I might of been close to tripping the circuit breakers. I thought if power amplifiers couldn't get enough power from the electrical circuit that the system would clip sooner because you'd have to drive levels higher in order to make up for the fact that the amplifiers weren't able to extract the amount of power neeeded.

[Mike Christy]

Ah right, so I won't get any higher spl out my system, it's just running my system with such small cable over such long runs only meant I might of been close to tripping the circuit breakers. I thought if power amplifiers couldn't get enough power from the electrical circuit that the system would clip sooner because you'd have to drive levels higher in order to make up for the fact that the amplifiers weren't able to extract the amount of power neeeded.

That would be somewhat true if you were on a long run and your primary voltage was dropping, say from 230V to 207 ( -10%) from cord resistance. The fact that you have the RMS series amps is a good thing, as they seem to be a bit more forgiving on a sagging supply than the light-weight current dependant amp topology.

Wish i could speak more about this, but I always try to have/spec good power, so haven't had much of an issue with this.

Mike

[david burns]

Thanks for your help Mike, I apreciate it.

[Tim Perry]

Place a volt meter at the amp rack.  Operate the system at 'normal' volume whatever that may be.  If the voltage drops more then a few percent consider using a large gauge cable.  (also check the source end to verify the drop is not excessive there. )

What is excessive? well that's kind of arbitrary.  If you get 3% at the mains and 3% at the amps that's  minus 6% voltage.  For me at minus 8 % or more some of the gear at FOH starts to get whacko. 

Another hint is if your cable gets warm to the touch it may be time to upsize.

When they melt, arc, or catch on fire it's pretty embarrassing. 

   

[Timothy J. Trace]

I love to trot this out any time I hear a discussion of ampacity in copper wire: http://en.wikipedia.org/wiki/Skin_effect

Enjoy   

.

[Poopedi Kwena]

I thought if power amplifiers couldn't get enough power from the electrical circuit that the system would clip sooner because you'd have to drive levels higher in order to make up for the fact that the amplifiers weren't able to extract the amount of power neeeded.

I thought so too. I thought insufficient power makes your amps clip quicker that they would with enough power because they will not be getting enough ampage/voltage (whatever the case it is) to produce what is being asked of them. And I also always thought power cables and power cords can be limiting factors to the flow of current into the amplifier.
Have I thought wrong too?

[Mike Christy]

I thought so too. I thought insufficient power makes your amps clip quicker that they would with enough power because they will not be getting enough ampage/voltage (whatever the case it is) to produce what is being asked of them. And I also always thought power cables and power cords can be limiting factors to the flow of current into the amplifier.
Have I thought wrong too?

Yes, a long run of undersized conductor may have enough resistance to create a voltage drop when you draw lots of current. The reduced voltage will degrade the amps performance. Clip early? Maybe, but clipping is usually from driving an undersized amp/rig to hard, add to that equation poor power then....

[Tim McCulloch]

I thought so too. I thought insufficient power makes your amps clip quicker that they would with enough power because they will not be getting enough ampage/voltage (whatever the case it is) to produce what is being asked of them. And I also always thought power cables and power cords can be limiting factors to the flow of current into the amplifier.
Have I thought wrong too?

The primary consideration is the total resistance of the copper path.   If you need less resistance (lower voltage drop) you need bigger wire.

How much bigger depends on how stable your incoming electrical service is to begin with, how tolerant of low voltage your amplifiers are and how much copper you put between the incoming service and your amplifiers.

Less drop is better, so in our systems we use the next wire size up from what the connectors/circuit breakers are rated for.  Typically you'd see #10 used for 30 amp circuits, we use #8 if the cable is over 25' (7.5m) long.  This is done to specifically address voltage drop that was calculated and predicted for the way we typically deploy our amp racks.

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