humming

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Old 12-05-07, 02:28 PM
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humming

Ok while changing the receptacles that I was just talking about I heard a slight humming at my circuit breaker panel box. I was able to figure out which one it was. It was my basement or my family room in my basement. At the time my son had the tv on as well as everything associated with it. I have a portable heater that I use down there so I turned that on and the humming was louder. Now prior to turning on the heater the humming you could hear only if you opened the door and stood very closely to the box, when I turned on the heater is was louder but again you would have to be right at the box so it is not extreme. Now I went ahead and switched out the breaker for a new one I had and yet had the same results. The panel is the old gould pushmatic from I would say the 1970's. Last week I had two seperate breakers trip, rightfully so though they were overloaded with Christmas stuff and I ran the electric leaf blower on one circuit and then ended up running a huge wet dry vac on another circuit a few days later. So I know the breakers trip when suppose to. Why though would it hum? It is a 20 amp line. Is this something that happens once you start getting close to overloading a circuit?
 
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Old 12-05-07, 02:59 PM
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This is likely normal, though it possibly indicates an overload. Heavily loaded breakers can hum. This is especially true for breakers that are moderately overloaded or about to trip. The only way to know for certain either way is to measure the current flowing on the circuit.

The simplest way to make this measurement is with a clamp on ammeter at the panel. All of the cautions about working in a live panel apply, in particular the exposed terminals at 120/240V and the unfused service entrance terminals.

-Jon
 
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Old 12-05-07, 09:24 PM
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Those portable space heaters are massive power consumers.
 
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Old 12-06-07, 03:36 AM
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Originally Posted by winnie View Post
This is likely normal, though it possibly indicates an overload. Heavily loaded breakers can hum. This is especially true for breakers that are moderately overloaded or about to trip. The only way to know for certain either way is to measure the current flowing on the circuit.

The simplest way to make this measurement is with a clamp on ammeter at the panel. All of the cautions about working in a live panel apply, in particular the exposed terminals at 120/240V and the unfused service entrance terminals.

-Jon
As Jon says, this is likely normal.
The reason is simple, the short sircuit protection part of the breaker is made as an electromagnetic coil, with a movable part to release the switch. This may cause humming, and it will increase by increased load. The only way to get rid of this is by getting a new breaker.

dsk
 
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Old 12-06-07, 06:14 AM
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The electric heater should probably be on a dedicated circuit. That alone might reduce the humming. Also based on my own experience I would occasionally "test" the plug by placing my fingers on it to see if I can hold them there for 10 seconds with out it being uncomfortably warm. I have seen plug blades actually eventually melt off. Also seen white receptacles turn brown and crumble from the heat. Even seen connections burn in two in a ceiling junction box because of a heater on a down stream receptacle.
 
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Old 12-06-07, 08:05 AM
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As far as replacing the breaker I did that and still same effect. But as the comment about the space heater using a lot of energy, you are right. I looked at the side and it said 1,500 watts so I assume that 12.5 amps are being used alone just for the heater along with the projection tv, the amp, and the direct tv box. I guess I am using close to 20amps and about to trip it when it is humming. Guys thanks for all your help and helping me understand all of this!
 
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Old 12-06-07, 09:06 AM
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Something that needs to be emphasized: breakers take time to trip, and will easily carry more than their trip rating for an extended period of time. The relation between the load on a breaker and weather it trips (or how long it takes to trip) is known as the time-current characteristic of the breaker. The trip characteristics have a certain tolerance range; at a given current level, one breaker might trip in 30 seconds, and another might take 60 seconds.

If you look at the time-current characteristic for a common breaker, you will see that (given the allowed tolerances), it might _never_ trip at 30% overload, and a 20A breaker could take 20 minutes to trip carrying 30A.

When you turned on that space heater, you probably overloaded the circuit, just for a short enough period that the breaker did not trip.

-Jon
 
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Old 12-06-07, 12:33 PM
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And if he has an old FPE box it might not trip till after the fire trucks arrive. You really need to run a dedicated line for the portable heater or better yet find a better heat source. Portable electric heaters are intended only for temporary use.
 
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