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I have a 15A circuit breaker in my electrical box tied to the media room. Every couple of weeks, it trips.

I bought an amperage/wattage load tester. Readings show 4 - 4.5A total in my media room...way under 15A. I suspect a malfunctioning device. To complicate matters, the tester can only read certain devices. I don't know if I have accurate readings.

The tester does not store max load over time. It only gives instantaneous readouts. I can't stare at the tester for weeks hoping for a problem to occur.

Losing power to my projector is bad. AFAIK there are no ceiling mount UPS devices either. Is there a tool to help me narrow the problem down to a specific device?

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4.5A for a media room sounds low - did you take that reading with all the gear on, or at an idle state? Devices like amplifiers can pull a lot of power when needed to drive big sounds. Does it trip while you are using it, or just randomly? –  Steven May 12 '12 at 16:21
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Replacing a breaker is pretty straightforward and not expensive. Get that done. –  Jay Bazuzi May 12 '12 at 19:05
    
This could be an intermittent short. –  Jay Bazuzi May 12 '12 at 19:06
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is this an arc fault breaker? –  Sam Miller May 13 '12 at 4:41
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Circuit breakers; like any mechanical device, can go bad. They are designed to fail open, so if the internal mechanism is damaged or not working correctly it will open the circuit. –  Tester101 May 15 '12 at 12:36

4 Answers 4

The only interesting information here is how many amps were being pulled on the circuit at the time the breaker popped. Breakers actually trip on heat, and a sign of a malfunctioning breaker is random inexplicable opening (tripping).

You could get yourself an Amprobe and watch it while a 'helper' turns things on and off and simulates normal activity in the room to see, however more than likely one of two things is going on:

  1. You have a bad breaker, just get it replaced
  2. Something (sump pump, maybe?) is also on that circuit, coming on weekly and tripping it

So, if you go the Amprobe route, you have to be there just at the right time to catch it. The event causing the breaker to trip might be happening fast enough for the tester you have not to notice it.

Replace the breaker (or have it replaced) first and see if the problem goes away. If it doesn't - figure out what's coming on at that interval that might be causing it. If the problem persists and nothing is suspect, have an Electrician take a good look at it, you probably have feeder somewhere that comes into contact with ground randomly.

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While the following maybe more unlikely it would certainly explain a possible trip, You dont know if that particular breaker is a residual current device (RCD) or a GFI/GFCI for those in the states. Computer equipment can be very susceptible to earth/ground leakage which in effect can cause nuisance tripping.

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I agree with @Steven. Total up your circuit and see where you stand on amperage if you cannot get an Amp meter. If you can get the wattage of each device on the circuit, then you should be under 1800 watts.

Breakers are designed to trip for two reasons, magnetic trips like shorts and thermal trips like the heat produced from over amperage. Magnetics usually trip quick, but not all the time and thermal is delayed, again not all the time.

Check your wattage or replace the breaker. Unless you have an older house with breakers that are obsolete, then the breaker should be relatively cheap.

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@Iqlarry - He has a 15A breaker, not a 20A breaker. Didn't you mean to say 1440 Watts resistive?:) –  SteveR May 13 '12 at 12:54
    
@SteveR There is a 20% rule you need to take off to follow code, but nobody told the breaker. The breaker is set to trip at 15 amps or 1800 watts. You are correct and OP should sort his circuit to follow this rule once he figures out what he has. –  lqlarry May 13 '12 at 19:13

First I would figure out exactly what loads are on the circuit, add the nameplate currents (or wattage) up. 120 watts is roughly equal to 1A. You can go up to 12A or ~1400 Watts on a 15A circuit. A breaker can be used up to 80% of it's rated value. Then think of what appliances are on when the breaker trips, time of day, etc. and see if you can correlate any commons. Measure the current with an Amprobe as Tim suggests, if you can.

Depending upon the current of the load, will depend on how fast the breaker trips. They are "Time over current" trip devices, meaning the more current the fault is, the faster the breaker will trip. You could have a 18A load, and it may take 5-10 minutes or so to trip a 15A breaker. One thing is for sure, you need to find this problem. Repeated overloads will cause the wiring in the circuit to heat up. This can cause expansion and contraction at electrical joints - screws, wire nuts, etc. Once they become loose it creates a high resistance path and that heats up even more. If you can not find the problem, you really need to call in an electrician.

This answer shows a graph of how a typical house circuit breaker will react. Notice at ~ 120% of rated load it can take up to 1000 seconds to trip the breaker.

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