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AC Outlet has 1.5 Volts with Breaker Off


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#1 Jon

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Posted 18 October 2011 - 05:46 AM

New to me old boat has 3 110/120 volt AC outlets with GFCI receptacles. Today I stuck my voltmeter into one of them and noticed that with the breaker off I was getting a reading of 1.5 to 1.7 volts. With the breaker on I was getting 122 volts. When I flipped the main AC panel breaker off, the meter reading went to 0 volts. It appears that some voltage is getting into the circuit even with the circuit breaker off.

I assume with the breaker off it should read 0 volts as well. Anyone have any experience or ideas on what is going on? How would you go about tracking this down?

#2 jocal505

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Posted 18 October 2011 - 06:41 AM

New to me old boat has 3 110/120 volt AC outlets with GFCI receptacles. Today I stuck my voltmeter into one of them and noticed that with the breaker off I was getting a reading of 1.5 to 1.7 volts. With the breaker on I was getting 122 volts. When I flipped the main AC panel breaker off, the meter reading went to 0 volts. It appears that some voltage is getting into the circuit even with the circuit breaker off.

I assume with the breaker off it should read 0 volts as well. Anyone have any experience or ideas on what is going on? How would you go about tracking this down?


I got a similar reading from a kitchen range outlet with the breaker off, was told that's pretty routine. Intriguing.




#3 amro

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Posted 18 October 2011 - 07:12 AM

ground loop back thru the neutral. your grounds maybe terminated in different locations causing a potential difference.

up here in canuckistan for transport canada certified vessels the neutral and hot are terminated on a two pole breaker. kills the circuit dead.

you probably have a metal thru hull or the like in the middle of the grounding/bonding system that is causing the small voltage.

#4 highndry

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Posted 18 October 2011 - 07:29 AM

many countries now require an inductive link between supply and boat

#5 floating dutchman

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Posted 18 October 2011 - 08:08 AM

New to me old boat has 3 110/120 volt AC outlets with GFCI receptacles. Today I stuck my voltmeter into one of them and noticed that with the breaker off I was getting a reading of 1.5 to 1.7 volts. With the breaker on I was getting 122 volts. When I flipped the main AC panel breaker off, the meter reading went to 0 volts. It appears that some voltage is getting into the circuit even with the circuit breaker off.

I assume with the breaker off it should read 0 volts as well. Anyone have any experience or ideas on what is going on? How would you go about tracking this down?

Wouldn't worry about it if you are measuring the voltage with a digital meter, I've seen much higher voltages just because the cable I was measuring was running close to a cable that was still live.

#6 Innocent Bystander

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Posted 18 October 2011 - 12:27 PM

Seems to be commmon with GFCI circuits whdn the GFCI breaker is off or tripped.

#7 Jon

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Posted 18 October 2011 - 05:02 PM

Thanks all for the info. I went to a seminar on a corrosion this summer not knowing what to expect and found out that most of what was covered was problems in the electrical circuits. Something I need to learn more about.

#8 sailSAK

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Posted 18 October 2011 - 05:25 PM

Phantom voltage... Very common especially on long run circuits when parallel feeds are live. I've measured as much as 20 volts before on a 'dead' circuit. You won't see anything on an analog meter. On a DC circuit however you might want to take a closer look!

#9 xyzzy

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Posted 19 October 2011 - 04:13 AM

Could be capacitance in the wire. You can measure a voltage on spool of duplex wire that's not even connected to anything. A good DMM can even measure an inrush of current when you first connect it.

#10 amro

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Posted 19 October 2011 - 09:55 AM

check to see if the neutral bus in the ac panel is bonded to ground. if so, i believe it's not supposed to be. the enclosure should be if it's metal tho. if you have a ground loop thru your bonding system it will at least stop coming into the ac system now. but then you'd have to track down the problem in the bonding. when we had this problem on a 120' yacht tracking it down was easy. we found several thru hulls were badly scorched. there was enough current flowing between the thru hulls into the bonding system to burn them.

#11 BFD

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Posted 19 October 2011 - 12:21 PM

New to me old boat has 3 110/120 volt AC outlets with GFCI receptacles. Today I stuck my voltmeter into one of them and noticed that with the breaker off I was getting a reading of 1.5 to 1.7 volts. With the breaker on I was getting 122 volts. When I flipped the main AC panel breaker off, the meter reading went to 0 volts. It appears that some voltage is getting into the circuit even with the circuit breaker off.

I assume with the breaker off it should read 0 volts as well. Anyone have any experience or ideas on what is going on? How would you go about tracking this down?


AC or DC? The answer is very important as AC ill not cause galvanic corrosion and DC will eat any metal in the water on your boat. Breakers, as they age, can leak small amounts of current but if any load is placed on it the voltage will disappear. You could also have what is know as a "leak to ground", usually from older equipment with electric motors and a neutral that is connected to the bonding system.

#12 jerryj2me

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Posted 19 October 2011 - 09:41 PM

Nope -- Leakage path with high impedance.

Try this:

Plug a lamp into the plug you are testing, or something that will draw current.

Now, go turn off the breaker and measure the voltage.
That 1.7 volts probably dropped to 0 or pretty close.

When you put a multimete across a plug, it does not provide any load, just measures a voltage.

If you have high resistance connected to power, you will see some voltage appear.
However if you load the plug down the high resistance path back to the power will drop most or all of the voltage.

#13 Conny71

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Posted 22 October 2011 - 03:47 AM

Induced voltage by running close to another live wire, no amps, just enough volts to make you ask the question.

#14 jerryj2me

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Posted 23 October 2011 - 10:24 PM

Induced voltage by running close to another live wire, no amps, just enough volts to make you ask the question.


Either induced voltage (think transformer) or resistive leakage, either can cause it.
Try the loaded line trick I suggest up above. If the voltage largely goes away its not a problem.

#15 awi

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Posted 28 October 2011 - 11:13 AM

I agree with earlier responses regarding induction or "no load" voltage.

Keep in mind that the galvanic potential of copper-zinc is 1.10 volts.

Also keep in mind that electrical potential follows the path of least resistance. The voltage that you measured could be tracking from another source far, far away.

It's no joke. It could fry expensive equipment or start a fire.

#16 awi

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Posted 28 October 2011 - 11:18 AM

I also agree that improper grounding could be part of the problem.




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