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Old 10-26-2010, 01:19 PM   #1
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Humming / vibration in electrical conduit


I'm getting a noise in a section of electrical conduit when there is a decent load on the circuit. The noise goes away when nothing is plugged into the circuit of the circuit breaker is off.

I have 1/2" EMT conduit with (3) 12 gauge wires (2 hot, 1 neutral) on 2 adjacent 20 amp breakers. The painters have (4) 500w lamps plugged into one of the circuits, nothing on the other. The circuit in use is showing 14.0 amps, the neutral is showing 14.1 amps.

Has anyone experienced this or knows what is causing this?

Jamie

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Old 10-26-2010, 03:03 PM   #2
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Humming / vibration in electrical conduit


How are you measuring the amperage?

You probably need to unplug everything that is connected to that circuit, and plug each back in, one at a time until you find the source.

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Old 10-26-2010, 03:56 PM   #3
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Humming / vibration in electrical conduit


It's literally only two extension cords plugged into two back to back outlets on a knee wall. One extension does a double light and the other extension goes to two single lights. These outlets are about 20 feet away from where I hear and feel the vibration. I can pinpoint the section of conduit to about 10 feet that seems the loudest. It all seems to be relative to the amount of current running through the line. I have almost full access to all of the conduit in question.

I don't know if one of the wires was damaged in the pull or not. If it was a short, the breaker should trip or I would expect it to happen under no load. Can the current create a magnetic force that creates the wires to bounce? It is just weird to me.

Jamie
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Old 10-26-2010, 06:54 PM   #4
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Humming / vibration in electrical conduit


Quote:
Originally Posted by codybear View Post
I'm getting a noise in a section of electrical conduit when there is a decent load on the circuit. The noise goes away when nothing is plugged into the circuit of the circuit breaker is off.

I have 1/2" EMT conduit with (3) 12 gauge wires (2 hot, 1 neutral) on 2 adjacent 20 amp breakers. The painters have (4) 500w lamps plugged into one of the circuits, nothing on the other. The circuit in use is showing 14.0 amps, the neutral is showing 14.1 amps.

Has anyone experienced this or knows what is causing this?

Jamie
Ok something is not adding up right in this one at all due if you have 1000 watt on one circuit which it will be about 8.3 amps on first hot conductor while second hot conductor it should read 8.3 amp as well but the netural if done right as we call MWBC if hook up properly you will have zero amp { I am not joking on this one so don't bluff on this one }

Which way you did ran the circuit on that one ?? and where you land it at the breaker ?? it should be right next to each other.

Merci.
Marc

P.S. the only time you will heard the conductor viberating in the conduit if the load is pretty hevey something like short circuit will do this pretty quick and motor load will be very common item to make noise in the conduit.
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Old 10-26-2010, 07:21 PM   #5
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Humming / vibration in electrical conduit


Marc:

Everything is on one circuit for a total of 2000 watts, but the clamp on amp meter is reading 14.0 on hot or 14.1 (on neutral) and 0.0 on the unused hot. I would have expected something like 16.7 amps, so I have to guess the (4) 500w bulbs are not really 500w each. As I said in my original post, the breakers are adjacent, so I'm not overloading the neutral. Yes, I am familiar with electricity's property of two circuits 180 degrees out of phase canceling each other out.

A slight update, the conduit in question contains only one hot and the neutral. The other hot had already been split off to do the front of the house. The noise, which is about as loud as an old model train transformer, appears to be happening around a 90 degree bend in the conduit. If I gently pull on the wire, I can cause the pitch to change slightly.

I'm tempted to pull the wire out to inspect it, but I'm not looking to create more work for myself.

Jamie
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