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Old 23-08-2017, 18:45   #1
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Electrical Leaks???

I have a 42ft mid cockpit sailboat. It is well equipted. In checking the Alt Current I discovered that there is a leak of .9 volt on the 115volt AC outlets when the Air Conditioning is on. This is true when these outlet circuits are turned off at the switchboard. All outlets are protected with GFCI. When the Air Cond. is turned off the .9 volt goes away . We are checking between the Hot load and the ground terminals with a multi meter. looking into the Webasto Air Cond control box we see nothing amiss but wonder if the capacitor is making the .9 volts ???? I seem to remember that there is always electricity in a capacitator -- but electricity is not may strong suit!Also wonder if the AC Ground and the DC Ground bus at switchboard should be connected. The Alt Current Ground is from a house where boat is docked and the house ground is a standard copper rod alongside house. Boat is in salt water 60ft away. help appreciated. Thanks.
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Old 23-08-2017, 22:58   #2
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Re: Electrical Leaks???

Can you explain exactly what and where you are measuring? I don't understand what you mean by "Alt current" and "leak".

Do you mean there is 0.9V measured between neutral and ground of AC outlets when Air Conditioning is on?
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Old 23-08-2017, 23:54   #3
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Re: Electrical Leaks???

I also have no idea what you are measuring... you should have 120v from hot to ground...

And yes the dc neg and ac ground should be connected at one point.
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Old 24-08-2017, 00:16   #4
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Re: Electrical Leaks???

If the problem is that you are measuring 0.9V between hot and neutral on a circuit that has been disconnected via a circuit breaker, you could be measuring voltage caused by capacitive coupling between powered and floating wires which will only be seen by a high-impedance meter. If so, this would not indicate a problem.

Or, you may have a big problem. We can't tell without some clarification.
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Old 24-08-2017, 02:21   #5
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Re: Electrical Leaks???

OK trying to be more specific: with the dock ac power cord connected and the 115volt outlets switched off at the switchboard and the Air Conditioner running(a webasto 16000 btu unit) there measures 0.9volts with the probes set on the hot and the ground points in the 15 amp 115 volt outlets . When the Air Conditioning is turned off there is no reading at these same points. So it seems that this voltage is there because the Air Conditioning is on.
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Old 24-08-2017, 05:25   #6
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Re: Electrical Leaks???

I think this is probably normal. Measure at one of the outlets the voltage between neutral and ground holes. Probably you will get the same 0.9V. If so, most likely what is happening is like this:

There are some appliances plugged into one or more of the 115 outlets in the boat. Therefore, there is a connection between hot and neutral due to whatever is plugged into the outlets. Even GFCI outlets have some high resistance between hot and neutral so maybe nothing has to be plugged in.

When the air conditioner is running the high current (about 15A) is causing the neutral bus to be about 1V different than ground. This difference also shows up on the 115V outlet hot terminal due to the aforementioned hot-neutral connections.

Probably there is a slightly high resistance somewhere in the neutral wire back to the dock or even in the dock wiring itself. Check your shore power connector at the boat and the dock for signs of heating. If there is no evidence of heating then I would not worry about 0.9V between hot and neutral.
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Old 24-08-2017, 05:34   #7
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Re: Electrical Leaks???

Is there a problem you're trying to rectify?

Do you have high current (over 500ma AC)measured on your shore cord with a clamp on meter?

Are you consuming anodes?
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Old 24-08-2017, 05:54   #8
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Re: Electrical Leaks???

Quote:
Originally Posted by transmitterdan View Post
I think this is probably normal. Measure at one of the outlets the voltage between neutral and ground holes. Probably you will get the same 0.9V. If so, most likely what is happening is like this:

There are some appliances plugged into one or more of the 115 outlets in the boat. Therefore, there is a connection between hot and neutral due to whatever is plugged into the outlets. Even GFCI outlets have some high resistance between hot and neutral so maybe nothing has to be plugged in.

When the air conditioner is running the high current (about 15A) is causing the neutral bus to be about 1V different than ground. This difference also shows up on the 115V outlet hot terminal due to the aforementioned hot-neutral connections.

Probably there is a slightly high resistance somewhere in the neutral wire back to the dock or even in the dock wiring itself. Check your shore power connector at the boat and the dock for signs of heating. If there is no evidence of heating then I would not worry about 0.9V between hot and neutral.
It is between hot and GROUND
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Old 24-08-2017, 06:16   #9
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Re: Electrical Leaks???

It is very common to measure fractions of a volt with today's sensitive digital meters. You can often put one probe between your fingers and see a voltage on the meter.

It's impossible to diagnose what you are measuring over the Internet but if you think you have a problem or a safety issue, I suggest bringing in a qualified marine electrician.
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Old 24-08-2017, 07:29   #10
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Re: Electrical Leaks???

Quote:
Originally Posted by geoleo View Post
OK trying to be more specific: with the dock ac power cord connected and the 115volt outlets switched off at the switchboard and the Air Conditioner running(a webasto 16000 btu unit) there measures 0.9volts with the probes set on the hot and the ground points in the 15 amp 115 volt outlets . When the Air Conditioning is turned off there is no reading at these same points. So it seems that this voltage is there because the Air Conditioning is on.
1. If the "AC power cord connected and the 115 volt outlets are switched off" ---
How is the A/C running with no power???

2. "There measures 0.9 volts between hot and ground" ----

This is nonsense. You have either 120 v between h and n or zero volts.

Please explain further.
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Old 24-08-2017, 07:50   #11
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Re: Electrical Leaks???

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Originally Posted by S/V Illusion View Post
1. If the "AC power cord connected and the 115 volt outlets are switched off" ---
How is the A/C running with no power???

2. "There measures 0.9 volts between hot and ground" ----

This is nonsense. You have either 120 v between h and n or zero volts.

Please explain further.
The AC outlets are switch off at the "SWITCHBOARD"- yet the dock power cord is powering everything else -- that is how the Air Conditioning is "ON" it is not nonsense Sir it is fact. The Air Conditioner is not plugged into a 115V outlet-it has its own switch.
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Old 24-08-2017, 08:01   #12
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Re: Electrical Leaks???

You say you are getting .9v from HOT to GROUND correct?,

Are you sure it's not from the Neutral to ground as this would be correct?trying to make this simple,the most common miss-wiring conditions are reversed hot and neutral wires and reversed or shorted neutral and ground wires.

1) Neutral-to-ground connection. Some neutral-to-ground voltage should be present under load condition (also called IR drop), typically 2V or less. If the voltage is zero with a load on the circuit, then check for a neutral-to-ground connection in the receptacle, whether accidental or intentional.

2) Reversed hot and neutral wires. Measuring hot-to-neutral voltage by itself doesn't tell you if those wires are reversed. You must measure neutral-to-ground or hot-to-ground voltage. If the neutral-to-ground is 120 V and the hot-to-ground is a few volts or less, then the hot and neutral wires are reversed.

NOTE: Hot-to-ground voltage. This reading should be the highest of the three readings. The ground circuit, under normal, non-fault conditions, should have no current and, therefore, no IR drop on it.

3) Hot-to-ground voltage. This reading should be the highest of the three readings. The ground circuit, under normal, non-fault conditions, should have no current and, therefore, no IR drop on it.

NOTE:Hot-ground can be thought of as the source of voltage available at the receptacle. You read 120.0 V. You note that hot-ground is higher than hot-neutral. In fact, hot-ground is equal to the sum of the hot-neutral and neutral-ground voltages.
The ground circuit, under normal, non-fault conditions, should have no current and therefore no IR drop on it. You can think of the ground connection as a wire running back to the source (the main panel or the transformer), where it's connected to the neutral. On the receptacle end of the ground path, where the measurement is being made, the ground is not connected to any voltage source (again, assuming there is not a fault).


Cheers Steve
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Old 24-08-2017, 11:08   #13
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Re: Electrical Leaks???

Folks, the OP told us that the AC outlets were switched off at the breaker panel. The air conditioning presumably has its own breaker. In this case one might expect to measure zero volts between hot and neutral (or ground) at the disconnected outlet. Instead, using a DVM, 0.9V is measured. The OP said they measured between "hot and GROUND".

* A high-impedance DVM is very sensitive, and as has been pointed out can detect voltage on your finger, or in this case on a length of disconnected wire. This is normal and usually does not indicate a problem.

* Depending on how the neutral wires are interconnected, the high current from the air conditioner may elevate the voltage measured between neutral and ground at the disconnected outlets. However, this doesn't seem to be what the OP is measuring.

I suggest that the OP plug in some low-power device (such as an incandescent night-light) into one of the switched-off outlets, then re-measure between hot and neutral at an adjacent outlet. If the voltage is not very close to zero there is a problem. What this test will determine is if we are seeing stray through-the-air coupling (the disconnected wires are acting as an antenna), or instead some potentially dangerous mystery connection.

It might also be instructive to measure between ground and neutral with the air conditioning on and off.
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Old 24-08-2017, 15:37   #14
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Re: Electrical Leaks???

Quote:
Originally Posted by transmitterdan View Post
I think this is probably normal. Measure at one of the outlets the voltage between neutral and ground holes. Probably you will get the same 0.9V. If so, most likely what is happening is like this:

There are some appliances plugged into one or more of the 115 outlets in the boat. Therefore, there is a connection between hot and neutral due to whatever is plugged into the outlets. Even GFCI outlets have some high resistance between hot and neutral so maybe nothing has to be plugged in.

When the air conditioner is running the high current (about 15A) is causing the neutral bus to be about 1V different than ground. This difference also shows up on the 115V outlet hot terminal due to the aforementioned hot-neutral connections.

Probably there is a slightly high resistance somewhere in the neutral wire back to the dock or even in the dock wiring itself. Check your shore power connector at the boat and the dock for signs of heating. If there is no evidence of heating then I would not worry about 0.9V between hot and neutral.
YEP there is a Microwave that has a clock in it that is always using some 115V!
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Old 24-08-2017, 15:40   #15
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Re: Electrical Leaks???

Now here is a related possible issue ---- I have not checked to see if the two grounds are connected-- I sure will though> If they are not the both the Generator and the Inverter will not have a ground!!! My My.
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