Subpanel question

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  #1  
Old 01-11-07, 08:16 PM
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Subpanel question

Hello. I have a 150 amp main breaker box in my basement with a 100 amp subpanel right next to it to feed my basement and my polebarn. In my basement, I have a small recording studio with some high powered gear. I have a 15 amp circuit that I plug the gear into and when I turn on the switch to my Monster power conditioner, the breaker trips. If I run an extension cord to an outlet that comes right off the main breaker box, it works fine. When I bring this same gear to a venue, I usually plug in and turn everything on without tripping a breaker. I have tried several circuits on that panel and also shut all the circuits off to make sure I wasn't over drawing.

The equipment is a 750 Watt bass amp, (2) 500 watt power amps, and several small effects processors. It all plugs into a Monster 3500 power conditioner and that plugs into the outlet.

What could be wrong here?

Thanks!
 
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  #2  
Old 01-11-07, 08:26 PM
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"What could be wrong here?"

=======================

you could be overloading the circuit. Have someone install a dedicated 20 amp recepticle for your equiptment.
 
  #3  
Old 01-12-07, 04:27 AM
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"What could be wrong here?"? Isn't it obvious? You have indicated 1750 watts, plus "several small effects processors". A 15 amp circuit can provide 1800 watts at maximum load.

As John said, install a dedicated 20 amp circuit.
 
  #4  
Old 01-12-07, 07:10 AM
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Guys thanks for the reply. I mentioned that when I plug the equipment into another 15 amp circuit (which comes off from the main breaker panel) it does NOT trip the breaker. It only trips the breaker when I plug into an outlet on the sub panel. Make sense?

Thanks!!
Brian
 
  #5  
Old 01-12-07, 07:19 AM
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There are many factors to be considered that you haven't addressed.

First, are you sure that the circuit right off the panel is indeed 15 amps? Did you look at the receptacle or the breaker to determine 15 amps?

Second, breakers are not exact. While a 15 amp breaker should trip at 15 amps, some will trip faster than others and some will trip a little above 15 amps and some will trip a little below 15 amps.

Third, what else is already on the circuit that trips the breaker? Lights? Another receptacle with something plugged in?

Fourth, is one circuit on the main panel and one on the sub panel?

Regardless of exactly why this trips in one receptacle and not in another, your load is too great for a 15 amp circuit. You definitely need a dedicated 20 amp circuit for this load.

If you really want to get to the bottom of this, then I suggest that you measure your load and answer the other questions. That should give you the answer.
 
  #6  
Old 01-12-07, 07:22 AM
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Guys thanks for the reply. I mentioned that when I plug the equipment into another 15 amp circuit (which comes off from the main breaker panel) it does NOT trip the breaker. It only trips the breaker when I plug into an outlet on the sub panel.
My first guess is that there's probably something else on the subpanel circuit (lamp, lights, etc), that add to the power load and push it over the edge.

Second guess would be that the subpanel breaker is newer (or older) and isn't quite as sensitive. When you power everything on at once, there's inrush current on the amplifiers which may only be for a split second. One breaker might handle the brief spike (>15A) by tripping, the other one doesn't.

Either way, I'd suggest upgrading to a 20A circuit (new breaker, wire & receptacle), or adding another circuit.

Edit: (Racraft beat me to these suggestions by 3 minutes. I guess he types (or thinks) fatster)
 
  #7  
Old 01-12-07, 09:27 AM
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There's nothing at all on the sub panel circuit except the circuit in question. I shut all the breakers off and it still trips. It sounds like the sub panel breakers are just more sensitive than the main panel. I realize that I am close to max on load so I will try the 20 amp circuit and let you know.

Thanks again!!
Brian
 
  #8  
Old 01-12-07, 09:59 AM
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You did not need to shut off all the other breakers. That was unnecessary and tells us nothing.
 
  #9  
Old 01-12-07, 10:20 AM
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Originally Posted by bassmanbrian View Post
There's nothing at all on the sub panel circuit except the circuit in question. I shut all the breakers off and it still trips. It sounds like the sub panel breakers are just more sensitive than the main panel. I realize that I am close to max on load so I will try the 20 amp circuit and let you know.

Thanks again!!
Brian
Like the others have said you're not testing it properly. The other breakers won't cause the circuit/breaker in question to trip. Here is what you need to do to test...turn off the circuit breaker in question but leave every other breaker ON...now go around in your house and see which lights don't turn on and/or what outlets are dead (you need a circuit tester for this...they run a couple of bucks at a home center)...now you have mapped out everything that pulls electricity from this circuit...either way if you have something that pulls 1700+ watts you need a dedicated 20amp circuit with 12 gauge wire...and based on some of your questions I would a.)hire an electrician or b.)get a good home wiring book to understand some of the concepts.

Regards
Doug
 
  #10  
Old 01-12-07, 11:04 AM
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Doug, what questions are you referring too? I don't recall asking any questions that makes me think I need to hire an electrician. I realize electricians have their place, but hooking up an outlet seems a bit extreme to me. I also realize you guys are trying to help and that is great, but why I always feel patronized when I come here is confusing to me.

So far, I am not doing a good job explaining. I can see that by some of the irritated responses!

Let me try explaining one more time:

Have a 150 amp MAIN breaker panel and ONE sub panel right next to it. I have ONE 15 amp circuit in the sub panel that is turned on. There is ONE 15 amp stand alone circuit (nothing on it) coming from the MAIN panel. The equipment plugged into the sub panel breaker will trip. The equipment plugged into the MAIN panel will not (both are 15 amp breakers with NOTHING turned on except the studio equipment).

I am installing the 20 amp breaker assuming that I just got lucky on the 15 amp coming off the main breaker panel. Will let you know soon.

Thanks,
Brian
 
  #11  
Old 01-12-07, 11:20 AM
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What else is on the same breaker as the 15 amp one that is continually tripping?
 
  #12  
Old 01-12-07, 11:26 AM
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> I am installing the 20 amp breaker

...and 12/2 wire, right?
 
  #13  
Old 01-12-07, 11:29 AM
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Originally Posted by racraft View Post
What else is on the same breaker as the 15 amp one that is continually tripping?
Well, I installed the 20 amp breaker, but still trips the breaker. I plugged back into the 15 amp outlet on the MAIN panel and it works fine. Nothing else is on the sub panel side. Same equipment being plugged into the circuit on the main panel. I have tried other equipment like computers, phones, lights, etc on the sub panel and everything seems fine. Just trips the breaker with the studio gear plugged into the Monster 3500. I have another sub panel going out to my polebarn (which is off for this test), and everything works fine out there (saws and power equipment). Probably not drawing as much as the studio gear.

Thanks for all your help,
Brian
 
  #14  
Old 01-12-07, 11:30 AM
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Originally Posted by ibpooks View Post
> I am installing the 20 amp breaker

...and 12/2 wire, right?
Ben, yes 12/2 wire.
 
  #15  
Old 01-12-07, 12:18 PM
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Crap, now I know you guys will really hammer on me! Actually, the circuit I thought was coming off my MAIN panel was coming from the sub panel. So, the 15 amp circuit that does work is in the sub panel. Why one breaker works and the other doesn't is a mystery.

Sorry to put you guys through this! Any other suggestions as to why one 15 amp breaker works and the other one (and the 20 amp breaker) does not work?

thanks,
Brian
 
  #16  
Old 01-12-07, 12:23 PM
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This is no mystery. Measure the current. I expect you will find that that the startup current is large. One breaker is either very tolerant in it's allowed startup current, or is simply bad.

Try starting the devices one at a time, and see what it is that actually puts the breakers over the edge.
 
  #17  
Old 01-12-07, 01:16 PM
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I got lucky and my electrician was available to stop by. He looked things over and said that the extension cord was acting as a "limiter" and that's why that breaker did not trip. Anything within a short distance was tripping. He suggested that it could be because my service panels are not commercial grade and all that equipment is professional grade grear. The bass amp causes quite a surge at power up and then settles down after it is running.

He is going to look into something that will help this situation and get back to me.

Have you guys heard of this? Not sure how much you all deal with pro audio equipment.

Thanks again!
Brian
 
  #18  
Old 01-12-07, 02:06 PM
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Plain and simple, this Monster 3500 is capable of handling 1800 watts and is a 15 amp device. I need to plug stuff into another circuit.

sorry to bother you all! thanks
 
  #19  
Old 01-12-07, 04:30 PM
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Brian,

You come back here ANYTIME fella and post away, you should never feel out of place asking questions here as that is what we are here for and not to make you feel out of place my friend.

Based on the loads you described in your original post, I would assume that you either simply had a breaker that was slightly variable tolerance or similar to cause it to trip on one breaker and not on another.

As for the extention cord powering it all and not tripping versus plugging right in....well the extention cord add's resistance so to speak and should have increased the likelyhood of it tripping...but alas...

However, as you have seen you are working with issues that mean you are possibly exceeding the rating of that breaker....are you running this for an extended amount of time before it trips.....all these things can be factors.

However, it sounds like you are on the right track and going to get a dedicated line for this use which should solve your problems.
 
  #20  
Old 01-12-07, 07:05 PM
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Thanks Paul! I appreciate that very much. It's hard having these virtual discussions! Not only for us posters, but also for the moderators I'm sure.

I did install a dedicated circuit and plan to run my big bass rig on a circuit by itself. Not how I wanted it, but my choices are limited. The bass rig pumps out 750 watts at 4ohms and 1000 at 2ohms! It's a beast, but it only comes in one flavor: POWERFUL!

Thanks again,
Brian
 
  #21  
Old 01-15-07, 10:44 AM
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Not to complicate matters, only as a clarification...

When determining the power requirements for an amplifier, you can't go by the power output (750w/1000w), you need to go by the nameplate rating. The nameplate on the device (also in the manual) will specify xxA at 120v. The xx is what you need to provide for when determining the circuit, etc. (15/20A, etc).

While the output is somewhat related to the power requirement, other factors such as the amplifier efficiency, fans, cooling, etc. all add to the input power requirement.

Anyway, I think your solutions/assumptions above are correct, but just wanted to add the clarification.
 
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