sub-panel for a recording studio


Old 09-11-01, 07:23 AM
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Alright, do-it-yourselfers, here's a good one. My buddy and his bandmates just bought a two flat in Chicago. They are converting the unfinished basement into a recording studio. Now, the building has two breaker boxes, each with a 100A main breaker. One of the boxes breakers add up to 175A, and the other box adds up to 215A (this box holds the breakers for the appliance circuit in the basement for the washer/dryer). They haven't tripped any breakers, so they aren't worried about changing their current breaker box situation around. What they would like to do is put in a sub-panel specifically for the recording studio. They have figured that they will need nine quad receptacles and one duplex receptacle, all 120V/15A. The meters are side by side and each one is rated/listed for 240V. is there a way to do this so they can put in a meter for the studio? And can someone direct me to a site with step by step installation for a subpanel?
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Old 09-11-01, 11:02 AM
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Do they simply want power, or do they really need a new meter? If so, what do they need the meter for?

Before we go too much further, we need to know not how many receptacles they need, but the power requirements (i.e., watts) of the things they plan to plug in.

You say they haven't tripped any breakers. Should I infer that they have already plugged in and used all their equipment somethere in this dwelling??

Adding up the breakers in a box is a meaningless exercise, unless you're just practicing your math.

How many empty slots are there in each of these panels?

Putting in a subpanel is probably feasible, but I doubt you're going to find step by step instructions on the web. Try visiting your local public library.
Old 09-13-01, 05:49 AM
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What John Nelson is referring to about adding up breaker values is that there is no requirement in the electrical code correlating sum of breaker values to the main breaker's value. You will seldom find a panel where the individual branch circuit breakers add up to less than the main. This is permitted due to the fact that you can't possibly have every single circuit running equipment at the limit of the individual breakers' value at once. And even if you could, once you hit the main breaker's capacity it'll trip, preventing you from pulling more current through your service conductors than they're rated for. The main breaker's value is therefore is dictated by the service conductor's amp rating by Code, and is there specifically to protect the conductors, not the box.

One example: I have a 150 amp/30-space panel. Few people use breakers less than 15 amps. If I fill 11 of the 30 spaces available with 15 amp breakers I've already exceeded the 150 amp main breaker. The breaker panel doesn't care, but I cannot exceed the capacity of my service entrance cable with that 150 amp main in the way.

As John indicated, more info would be needed to advise further. Answer some of his questions and we should be able to help more.

Old 09-13-01, 09:02 AM
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Continuing with Juice's example, you must remember that the 150 amps he has in his panel is at 240 volts. This is equivalent to 300 amps at 120 volts. So he'd really need 21 of those 15-amp 120-volt breakers to even have a chance of exceeding his main breaker. However, even if he filled up all 30 slots with 15-amp breakers, he would still be within normal limits.

This is a very simple example that ignores the fact that all panels have a few 240-volt breakers too.

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