Electrical hum, noises etc....

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Old 12-29-15, 06:30 AM
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Electrical hum, noises etc....

Just wonder....are the electrical noises in outlets, light switches, light bulbs etc... the same phenomena or there are many different reasons ?

I am just curious.... don't have a concrete example right now....just was thinking about it....I think once I could hear very low hum in an outlet with no load...or a kitchen light noise coming from the switch.

This is just about outlets, lights....not about noise /hum associated with motors or other electromagnetic devices.

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Old 12-29-15, 12:39 PM
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It is possible to hear hum at a receptacle. It would signify a sizable load being drawn thru it and it not being a 100% tight connection. This would create heat.

A back stabbed receptacle could hum. If you hear a hum in a device ..... it needs to be looked into.

Bulb filaments can resonate to 60hz line voltage and appear to be humming.
Newer CFL and LED bulbs have transformers/inverters/converters in them and can also hum.
 
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Old 12-30-15, 10:19 AM
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is it possible to hear hum at the receptacle when there is no load?
I mean, nothing plugged in and lights off....?
 
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Old 12-30-15, 10:29 AM
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Receptacles are often/usually daisy chained, one receptacle feeding the next and so forth. Therefore a load may be being pulled through a receptacle even if nothing is plugged in. If multiple loads are plugged into the same circuit the amount of current through the receptacle will equal the sum of the loads.

Note: This is one of the reasons aluminum 120v wiring is so insidiously unsafe. A fire can start in a hidden and forgotten unused receptacle because of power being pulled through it.
 
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Old 01-05-16, 04:08 AM
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what is "back stabbed receptacle" ?

So in essence if one is certain there is nothing connected to any outlets in a circuit then the cause of any hum/noise would be lose connection ?

Can you also hear the noise if somebody used 14AWG with 20Amp circuit...as that would also generate heat...or would the 14AWG wire only get hot when load above 15Amp is applied to the circuit ?
 
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Old 01-05-16, 06:55 AM
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Anything with a transformer in it can have hum as part of normal operation. Transformers have iron cores and the magnetic forces produced by the AC current can cause them to vibrate slightly in their mountings. Higher quality (more expensive) transformers are built more robustly and vibrate less, therefore making less noise.

Light bulbs can sometimes hum due to a similar vibration effect with the filaments.

Receptacles and switches in my opinion should be silent. Any noise coming from these is the result of a loose, sparking connection which needs repair. However much like working on an engine, sounds can travel through solid materials, and I think it would be very difficult to pinpoint where the sounds is actually coming from vs. just radiating along the framing or sheetrock.

Backstab connections on receptacles and switches are the holes on the back of the device you just push the wire in to instead of wrapping it around the screw. There is a spring mechanism that pinches the wire in place and it wears out with use causing the connection to get weaker.
 
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