# Closed switches or breakers have noise voltage?

Discussion in 'General Electronics Discussion' started by Danny Daviss, Mar 20, 2013.

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1. ### Danny Daviss

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Mar 16, 2013
When I close a switch or close a breaker and taking a reading on my DVM, I need a voltage , it should be zero volts , but I get 3 volts from the induced voltage or noise?

Why is that?

2. ### Danny Daviss

67
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Mar 16, 2013
it should be zero volts closed and 120 AC when switch or breaker is open

But I'm reading 3 VAC when the switch or breaker is closed , why is that? is this an induced voltage or noise with voltage?

3. ### CocaCola

3,635
5
Apr 7, 2012
Anything else on the circuit that might be back feeding?

4. ### Danny Daviss

67
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Mar 16, 2013
what's back feeding?

When the switches or breakers are closed they should be Zero volts to ground

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
Are you measuring to ground or neutral?

Try measuring between neutral and ground. I bet you'll find a few volts there if your ground isn't bonded to neutral or if there's a high neutral current.

If there's a load attached, then active will go to the neutral potential when the circuit breaker opens (unless something is back-feeding it as CocaCola suggests).

Don't kill yourself doing this.

6. ### CocaCola

3,635
5
Apr 7, 2012
Maybe it should be zero, are you measuring neutral or ground? Because neutral backfeeds are quite common in structure wiring... They can be aggravated by an imbalance system or the lack of proper bonding to ground...

Are you one in the same with Danny Davis

If so I guess we are back to suggesting GOOGLE...

http://en.wikipedia.org/wiki/Backfeeding

7. ### Danny Daviss

67
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Mar 16, 2013
measuring neutral to hot which is 120 VAC

Measuring Neutral (white wire ) to ground i think or its neutral again to a breaker

One side of the switch goes to HOT , the other side of the switch goes to either neutral or ground

But when I'm measuring the AC voltage , I measure with my black probe to the neutral white wire to the HOT sided lug when the switch/breaker is open, It reads 3 VAC when the switch is open and I'm measuring with my DVM meter from the white neutral wire to the HOT black wire sided lug on the switch

I get 3 VAC when the switch is open, measuring from the HOT side of the switch/breaker lug terminal to the white neutral wire

8. ### CocaCola

3,635
5
Apr 7, 2012
Nope, one side of the switch should go to to hot, the other side goes to the fixture, neutral also attaches to the fixture and you have a circuit...

Sorry can't follow what the heck you are doing...

As Steve and I stated neutral and ground are NOT the same, neutral will in many cases hover above ground, it's not proper but it's quite common...

I'm of the opinion that if you don't understand mains wiring (it's clear you don't) then you have no business playing with it unless you are under the direct supervision of someone that does understand it...

9. ### Danny Daviss

67
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Mar 16, 2013
Yes I'm measuring from the HOT to the fixture, when the switch/breaker is OPEN and it measures 3VAC why? the switch is open and there is AC voltage

10. ### CocaCola

3,635
5
Apr 7, 2012
I have already told you, something is back feeding, you have an imbalanced load or your neutral is not bonded properly... There are other things that can aggravate this effect as well, long runs of wire (electricity follows the path of least resistance even it's the wrong path) or improperly wired reversed polarity sockets (potentially back feeding)...

11. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
I'm still not sure what you're measuring. You have only mentioned HOT (active), and not what you are measuring it with respect to.

Since it appears the load is a globe (maybe??) then it connects the now isolated active to neutral. Presumably you are measuring the isolated active to ground which is essentially the same as measuring from neutral to ground.

Mind you, I have to make a lot of assumptions because you write a lot of words, but tell us very little.

12. ### Danny Daviss

67
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Mar 16, 2013

What does neutral is not bonded properly mean?

13. ### Danny Daviss

67
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Mar 16, 2013
Respect to Neutral

The Breaker has 2 terminals
1.) HOT on one side
2.) Neutral on the other side

I'm measuring when the Switch/breaker is OPEN which measures 3VAC , why? it should be zero volts since the breaker/switch is OPEN not closed

25,482
2,830
Jan 21, 2010