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Discussion Starter · #1 ·
Hey all,

I handle all the sound and lighting in the auditorium at my local high school. Our sound system consists of 3 CTs 1200 and 1 CTs 2000 amplifiers connected to eight speakers, plus a less than stellar mixing board and even worse wireless mics. We had a gig last week where some live bands played and sang as well. Unfortunately as you can probably guess, guitar players insist on playing extremely loud which meant I had to increase the volume of the vocals to compensate. When I did this it popped the breaker switch, something which has never happened before (it's a new auditorium, just over a year old), I then found out that whoever ran the power or installed the sound system put all 4 amplifiers and the rest of the sound stuff onto one breaker circuit.

Is my assumption correct that each amplifier should have been on their own breaker circuit?

My school needs concrete proof that somethings wrong rather than just word of mouth from me.

Thanks!

Matt
 

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Well Mam,
The easiest way to identify the potential of over-amping your circuit is simply identify the potential amperage requirement of an amp then multiply by 4 or whatever numbers are used on a single circuit.

If you look at the back of the amp you will find an amperage rating. It will be a number and a capital "A" somewhere after the "Output:", I expect you you will find an 8 to 12A potential requirement somewhere below the model number. This amp rating does not mean the amp will always draw the stated amperage however it does have the potential.

You might also check the amp rating of the fuse in use in each amp. But the amp rating on the back of each amp is a very concrete statement. You might recommend a dedicated 20A circuit and breaker for each amplifier. Check into wiring a single receptacle on a dedicated circuit or not. I forget how many duplex receptacles are typically acceptable in a wired residential service (4 or more).

I hope this helps and I hope you find a professional to do the actual work. Do not cut corners with electric power.
-Greg
 

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Discussion Starter · #3 ·
Hey Greg,

I actually did the above and got around 46.8 amperes, and its all being ran off of a single 20 ampere circuit. Granted I know I won't be running at full output all the time, but there is the occasion when I need to push the system a little bit.

I'm looking into running dedicated circuits for each amplifier, but I'm running into the problem of whether our less than 1 year old auditorium has any conduits for running extra wiring underneath it.

Thanks Greg, and don't worry, I won't be doing any of this myself, way too risky.

Matt
 

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It is common to use the 1/8 power pink noise rating of the amp to determine the mimimum AC requirement for "nominal" use and 1/3 power for heavy duty use.

For a 1200 driving 4 ohm loads this would be 10 amps and 16 amps. 8 ohm loads would be less.

For a 2000 driving 4 ohm loads this would be 7 amps and 12 amps. 8 Ohm loads would be less.

Go to http://www.crownaudio.com/amp_htm/ampinfo.htm#b02 and download the sheets for the two amps.
 

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Great Mam,
I hope the Board takes this as seriously as you are. I understand budgets are tight but I think you have what you need to make a strong case for dedicated feeds.

I hope you all have lots of fun with learning at your school. Take good care.

Greg
 

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The current draws listed on the amp are considering the amp is running at 1/8th power. This is probably a reasonable assumption for most amps running tops. But if you are driving subs this number is probably way to low ( like by a factor of 2 or 3).
 

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Agree with Voxman. Two 20 amp dedicated circuits will probably do what you need. Obviously more is better but if you can start with this you will be OK.

Tell the administrators that each time an amp shuts down it has the potential to literally blow the speakers and the amp. Modern amps are well protected against these things but anyone in live sound long enough has melted an expensive speaker at least once. You can tell them that I am an electrical engineer with 30 years experience and a trained sound engineer. You can send in a question to my website and I can write you an answer back if that will help.

Good luck.
 
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