AC Electrical green wire current?

[smokey73]

Was checking my AC wire current flow for my Nextgen 5.5 KW Generator.

As per my understanding of the correct wiring for an onboard generator from @Maine Sail how to site by white and green wires are connected at the generator.

Using a clamp on ammeter on the three wires I get the following readings:

Black (power lead) 9.50 Amps
White (common) 9.15 Amps
Green (ground) 0.45 Amps

What gives? If my understanding is if the wiring is correct the Black and White should read the same current and there should be no current on the Green wire unless there is a leak or some other miswiring somewhere?

Any help would be appreciated.

One troubleshoting method I read in Practical Sailor awhile back is to measure the resistance between the white and the green wires (with no power on). If it is wired correctly there should be OL (open or infinate resistance) between these two points. If it is anything but OL then there is a leak between common and ground somewhere or a miswiring.

Smoke

 

[mermike]

What did your get when you measured the resistance? If your generator has a ground relay, and it should, it needs to be closed to check continuity. I should also ask how good your clamp meter is and whether you calibrated it.

 

[smokey73]

What did your get when you measured the resistance? If your generator has a ground relay, and it should, it needs to be closed to check continuity. I should also ask how good your clamp meter is and whether you calibrated it.

I haven't done the resistance check yet, I just read about it today.

I'm not sure about the "ground relay" you mention. I believe the Nextgen meets ABYC standards. What does the ground relay do?

As far as calibration, I am not sure of the method for that but I'm more interested in "relative numbers". With the same load I am showing a currnt in the grean wire. I was under the impression that if the wiring is correct and there is no leakage, the current in the black and the white wires should be the same and there should be no current in the green wire. Is that not correct?

 

[mermike]

The ground relay connects the ground and neutral when the genny is in operation. When it is not, the relay will be open. Your neutral will be joined to the ground at the power source, whether it be shore, inverter or generator.

i have to zero my clamp meter (a Fluke i410) when I plug it into my multimeter, and frequently forget to do so.

 

[Davidasailor26]

Sounds like something is leaking to ground. What loads did you have turned on when you took the measurements?

One troubleshoting method I read in Practical Sailor awhile back is to measure the resistance between the white and the green wires (with no power on). If it is wired correctly there should be OL (open or infinate resistance) between these two points. If it is anything but OL then there is a leak between common and ground somewhere or a miswiring.

Do you have a transfer switch between shore power and generator? If so then putting it into shore mode and leaving the shore cord disconnected should allow you to run the above test. When the generator is enabled the ground will be connected to neutral, so you’d expect to see continuity between those two. When in shore mode the ground should not be connected to neutral anywhere on the boat, so you should see an open circuit. Any connectivity between the two would be a leak.

 

[smokey73]

@Davidasailor26 - Exactly what I was thinking. I do have a transfer switch that allows me to select off, Shore, Generator. I don't think I have a ground relay on the generator but when the transfer switch is in Generator, the neutral (white) and green are connected. When in off or shore I should not have any connection between neutral (common) and ground so should get open circuit with this test. I should be able, with the transfer switch in Off to do the test and tell if it is is before the transfer switch. If its open circuit with the transfer switch in off but shows some resistance with the tansfer in Shore, the the problem is between the transfer switch (or the switch itself) and the shore power connection (including the shore power connection). All of these tests are done with the shore power cable not connected to the boat. Is that logic correct?

 

[Davidasailor26]

Since you were reading current on the green wire when running the generator the leak must be on some part of the circuit that was powered up when the transfer switch was in generator mode. You can do the test like you describe just to make sure, and you’re right that all continuity tests should be done when the shore power is disconnected and the generator off.

Since you’ve already established that there’s current on the green wire you’re probably going to need a way to narrow down where the leak is. To do that I’d start by running the generator with all appliances (anything with a plug, water heater, battery charger, etc) turned off, and the generator on. Confirm that there’s no current on any of the wires. Then turn on loads one by one and check for current on the green wire. The load that causes current on the green wire is leaky, or on the leaky circuit. If multiple different loads cause the current then some shared wiring between them is the leak.

 

[smokey73]

@Davidasailor26 sounds like a plan . Thanks

 

[JamesG161]

narrow down where the leak is.

Number 1 suspect would be any 120VAC receptacles with a GFCI circuit breaker.
They "leak" as they age, even without a load on them.

Also @smokey73 a good time to put your new AgCl reference probe in the water too.
Check you Zinc potential at the same time.

Fun times being a Marine Electrical Tech.

Jim...

 

[Benny17441]

Before getting into the boat wiring; connect jumper leads to a known good appliance and measure the voltages again. If they have not changed they either emanate from the generator or a faulty meter. Take direct readings with wire leads (take proper precautions) instead of the clamp and compare.

 

[walt]

If your generator has a ground relay, and it should,
The ground relay connects the ground and neutral when the genny is in operation

when the transfer switch is in Generator, the neutral (white) and green are connected.

I dont have a system like this.. and maybe read things wrong.. but it sounds like the green and whte get connected at the generator by a relay. And the green and white (nuetral) get connected together at the transfer switch.

Ie, you have a parallel run of white and green between the generator and the transfer switch. Current through this parallel set will be determined by the impedance of each wire run.. If the impedance were identical between white and green, you would get equal current in each wire. If the impedance of the green wire is higher (maybe because of a relay and switch contacts), you would see higher current in the white, less current in the green.

.45 amp isnt really in the realm of leakage and the white to green measured current ratio is 21.. but impedance will be very small and 20 times very small is still small.

Just a thought.. and I dont think there is a corrosion or safety problem with the setup if this is the case..

 

[JamesG161]

I do have a transfer switch that allows me to select off, Shore, Generator

There is a difference between a Selector Switch and Transfer Switch.

The Selector Switch is what I think you are referring too. I believe only the white wire.

A Transfer Switch moves all 120VAC three lines at same time to prevent the Generator from back feeding to Shore Power.
Jim...

 

[smokey73]

There is a difference between a Selector Switch and Transfer Switch.

The Selector Switch is what I think you are referring too. I believe only the white wire.

A Transfer Switch moves all 120VAC three lines at same time to prevent the Generator from back feeding to Shore Power.
Jim...

Let me check when I get to the boat late this week and I'll post a sketch. But the "switch" (be it transfer or selector) connects both the AC black and AC white from which ever source is selected to the boats Black and White wires that then go to the main AC breaker on the boat electrical panel.

Thus, when the selector switch is in Shore, the Shore Black and White are connected too the AC breaker through the "Switch". The green made a direct run to the Galvanic Isolator then to the AC shore power plug. The green and white wires are not connected together on the boat.

When the selector is in Gen, the Gen Black and Gen White are connected to the AC breaker through the "Switch". The green then goes to a lug on the ship side of the Galvanic Isolator (bypassing the GI) and then connects to the white wire at the Generator.

Note that I show the same 0.4A current when I put the clamp on Ammeter on my shore power cable at about a 10A load. I was expecting to see 0 amps. That's what started all this questioning in my mind. Maybe I"m misunderstanding something about what I should be reading and making a problem in my mind when there shouldn't be one. Maye its something in my meter too?

 

[Davidasailor26]

I think the wiring arrangement you’ve described is proper. The important points are that the green and white are not connected on the boat when in shore power mode, and they are connected at the power source when in generator mode. But in either case there should be no current on the green wire unless there is a fault somewhere.

Note that I show the same 0.4A current when I put the clamp on Ammeter on my shore power cable at about a 10A load. I was expecting to see 0 amps.

You’re right to expect 0 amps measuring on the cord. If accurate, a reading on the cord is bad news, and means that portion of the current is returning to ground through the water. The fact that the amperage is roughly the same as is on the green wire when in generator mode is interesting. Makes me think it’s caused by the same fault, and the GI is not properly conducting AC along its ground path.

 

[JamesG161]

But in either case there should be no current on the green wire unless there is a fault somewhere.

Or from another boat nearby.

Thus the reason I suggested that @smokey73 put his new AgCl reference probe in the water, during his hunt.
Jim...

PS: When on Shore Power, that ground is for your boat too , near their meter box.
PSS: When on Generator, your boat's Ground is in "charge" [pun intended]

 

[mermike]

I should have clarified that connecting the ground and neutral could be done by a transfer switch or a ground relay. There should be one or the other.

I agree with other posters that any voltage on your ground wire is cause for concern. You've been offered 3 troubleshooting paths:

1. Test for current on the ground by adding or subtracting loads, one at a time.
2. Test/replace GFCIs.
3. Test for galvanic issues with your AgCl reference probe.

You might also test your galvanic isolator. Here's a link to marinehowto.com on that procedure.

 

[walt]

You’re right to expect 0 amps measuring on the cord. If accurate, a reading on the cord is bad news, and means that portion of the current is returning to ground through the water. The fact that the amperage is roughly the same as is on the green wire when in generator mode is interesting. Makes me think it’s caused by the same fault, and the GI is not properly conducting AC along its ground path.

Just a thought.. if you actually have leakage into the water from a fault where some underwater structure has a voltage applied (like the hot wiring touching it), you will see that current in a difference reading between white and black but you wont see that current on the green - because the current is returning through the water and not through the green.. Current leaking into the water would also tend to be about the same regardless of loads on the boat. (ie, if the underwater object is at 110V, current into the water would be dependent on the conductance from the object to the water only).

You mentioned a case of a load where
Black (power lead) 9.50 Amps
White (common) 9.15 Amps
Green (ground) 0.45 Amps

If you have half the load, do you still get the same ratio of currents on the three wires? Ie, if the Black is 4.75 amps, is the green current now .225 amps. Just another guess but this is more of what you would see if you did have some equipment ground fault on the boat.

 

[Davidasailor26]

if you actually have leakage into the water from a fault where some underwater structure has a voltage applied (like the hot wiring touching it), you will see that current in a difference reading between white and black but you wont see that current on the green - because the current is returning through the water and not through the green.

Correct when the transfer switch is in shore power mode. But it sounds like the initial reading of current on the green wire was when the transfer switch was in generator mode.

Current leaking into the water would also tend to be about the same regardless of loads on the boat. (ie, if the underwater object is at 110V, current into the water would be dependent on the conductance from the object to the water only).

That depends on where the current is leaking from, I think. For example if the current is leaking through the water heater, then the problem will only be visible when the water heater is powered on.

 

[walt]

Note that I show the same 0.4A current when I put the clamp on Ammeter on my shore power cable at about a 10A load

.

I took this (from the OP) to mean that the current on the green wire was about the same for either the genset or shore power.. If so.. the problem is likely down stream from the transfer switch.. Is this correct, you get the same leakage numbers for the transfer switch on Genset or when the transfer switch is on shore power?

 

[Davidasailor26]

.

I took this (from the OP) to mean that the current on the green wire was about the same for either the genset or shore power.. If so.. the problem is likely down stream from the transfer switch.. Is this correct, you get the same leakage numbers for the transfer switch on Genset or when the transfer switch is on shore power?

I see. That’s not how I read it; I guess the OP can confirm. I assumed he put the clamp over the whole shore power cable, thus measuring the imbalance between the black and the sum of the white and green.