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Old 06-27-2016, 10:42 AM   #1
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Voltage between neutral and ground?

I was working on some wiring for the outlets circuit and with the branch distribution breaker off, (only turns off the hot black side), I noticed a small spark between neutral and ground when touched together. However no shocking event for me touching those wires.

So that surprised me. The circuit is GFCI protected and the GFCI tests good and the GFCI does not trip when the breaker is on and the outlets are used.

I need to use my meter and measure what that voltage is.
Any ideas what it is? I was sort of thinking since all my white neutrals are tied together in the distribution panel, and the AC was on and a few other AC devices, would not some return current flowing on the neutral white wire also flow onto the ground when deliberately touched together? The ground would then become an alternate pathway for current flow. And afterwards I did notice the GFCI had tripped off. So when I finished with the wiring, I reset the GFCI and everything is fine.
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Old 06-27-2016, 10:58 AM   #2
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Not sure how your boat is set up, but the panel that holds that breaker may be a sub-panel ie power to that panel comes from a 'master' panel. If that's the case the common/neutral wires and the ground wires must be on separate buss bars that are not bonded ie connected via any wire or via the metal panel box - if not then the common and ground wires will indeed be able to carry some current - very common mistake in homes as well as boats. Can be dangerous - but I've seen new homes with this mistake pass inspection.
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Old 06-27-2016, 11:17 AM   #3
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FC aren't neutral and ground supposed to be connected somewhere? In that case why would there be any voltage difference unless there is a poor connection somewhere? Or one of the AC devices is not grounded?




Shadow is there any evidence of stray current on zincs or bottom paint?
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Old 06-27-2016, 12:02 PM   #4
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Panel does not join neutral and ground, they are separated, have no continuity. So yes like a subpanel, the neutral to ground bond is on shore at the point of origination for utility power. Boat is like an appliance you plug in.

The ground only carried some power when I touched the white neutral wire to the green ground wire, hence it was doing its normal job. White wires does carry all the return current back after the current leaves an appliance. I think the green ground wire was just shunting some current as an alternate pathway back to home
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Old 06-27-2016, 12:09 PM   #5
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If the neutral isn't carrying the same as the hot on any circuit in the boat, especially the power cord...there is a problem.
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Old 06-27-2016, 09:59 PM   #6
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The green ground is connected directly to Earth at many places including your house and the boat’s bonding system. The neutral is connected to Earth at the power generating facility but nowhere else. At your house (or boat) it is possible to get a small potential between the neutral and Earth (green ground) by virtue of the current flowing through the circuit and the finite resistance of the wires. Note that the same current flows through both the “hot” and neutral wires.

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Old 06-27-2016, 10:27 PM   #7
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IF you have a Galvanic Isolator There will be a potential between ground and Neutral on the boat... Especially if the capacitor is bad or there isn't one in the GI. Marine application do not tie the neutral and ground together because the ground is used as bonding If they were tied together it would be possible to electrify the surrounding water
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Old 07-03-2016, 01:56 PM   #8
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Quote:
Originally Posted by Paul Swanson View Post
The green ground is connected directly to Earth at many places including your house and the boat’s bonding system. The neutral is connected to Earth at the power generating facility but nowhere else. At your house (or boat) it is possible to get a small potential between the neutral and Earth (green ground) by virtue of the current flowing through the circuit and the finite resistance of the wires. Note that the same current flows through both the “hot” and neutral wires.

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Maybe it's just terminology, but as I'm reading it I don't think it's correct.

Ground and Neutral are supposed to be bonded (connected) at the "power source", and only at the power source. What constitutes the "power source" varies, especially on a boat. When you say "power facility" I take that to mean the power generation plant, but this may be where I'm just not understanding your terminology. The power coming out of a generation plan actually has no neutral.

Here are some examples of proper neutral/ground bonding under different circumstances found on a boat:

1) When on shore power, the power source is the land power system. Land power systems have neutral and ground bonded at the main breaker/meter panel, so the neutral and ground are already bonded when they reach the power stand at your dock. That is carried through to your boat, so when on shore power there should not be any neutral/ground bond on your boat.

A galvanic isolator does not change this. It carries the ground through to the boat - sort of. It isolates the shore and boat grounds as long as there is no more than 0.7V difference between them. But if there is a difference greater than 0.7V, as in the case of a fault being protected by the ground, it ties them together.

2) Running on the boat's generator. In this case, the generator is the power source, and there neutral and ground should be bonded there. The trick is to have this bonding be in place when powered off the generator, but not when powered off shore power. Most setups I've seen have ground and neutral bonded in the generator, but the power selector switch that selects between gen or shore power breaks the neutral when the generator is deselected, thereby also breaking the neutral/ground bond.

3) Inverter power. In this case the inverter is the power source, and neutral and ground should be bonded there. This is where it starts to get complicated because many inverter setups operate with and without shore and gen power. What is bonded where and when gets complicated.

3A) Inverter only. If shore and gen power are off and you are only running on inverter, like at anchor, then bonding should be at the inverter.

3B) Inverter with gen or shore power operating. When either shore power or the gen is operating and the inverter is either passing through AC power, or operating in charger mode, then bonding should be at the gen or shore power as previously described since they are the power source. Some inverters have internal relays that will create or remove the bonding connection based on the presence or absence of input AC power. Other rely on it being handled correctly external to the inverter.

This is probably more than you wanted to know, but might help you track down and fix the problem without creating a different problem at the same time.

But the bottom line is that you should not be seeing any voltage difference between neutral and ground.
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Old 07-03-2016, 04:10 PM   #9
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The inverter, if a proper marine type, will automatically join the neutral and ground when turned on. Same with your generator. With inverter and generator off, their should be absolutely no continuity between ground and neutral. Unless you are absolutely positive that you know what you are doing you should not play with this as it is potentially lethal. Consult an ABYC Certified electrician if you have any questions at all and hang over his shoulder while he checks.

PS. GFCI's don't live forever. Just because they are passing power does not mean they are working properly.
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