Reverse Polarity with Generator

[Andy B]

Onan uses a 40 amp brk so it work wired 240 and 120 .when the gen is wired 120v. the brk needs jumped,it was installed incorrectly a good tech will be able to sort it out.

[Vincentc]

I contacted Magnum regarding the question of whether the Inverter install could be causing the polarity issue and Darren at their tech support replied (confirming what Pete said):

The issue you are describing is usually caused by a loss of the ground connection. I would check back at the generator and make sure you have a good ground and that the neutral and ground are bonded at the generator.

I checked the ground connection between the generator case and the bonding strip running alongside the port engine stringer. That connection is good; however, nearby connections between the bonding/grounding strip and thru hulls and the engine support were broken at the terminals. I guess that is to be expected in a 30 year old boat. Not sure if those bad connections would affect the generator ground. I assume that more important are the grounding wires connected to strap inside the generator, and whether they are properly connected to the grounding buss at the main panel.

I am going to have on a qualified technician check and correct the installation, but would like to understand the problem.

Thanks

[MikeP]

A few thoughts...

The wording is a little confusing to me:

". I would check back at the generator and make sure you have a good ground and that the neutral and ground are bonded at the generator."

I frankly can't tell if the tech is saying that:

the generator's ground (green) wire and the generator's neutral (white) wire are to be connected together ("bonded") at the genny and then there is a wire from that connecting point to the ground buss.

OR

If he means the ground/neutral are connected at the genny and then a wire is run from that connection to the neutral buss

OR

If he means the genny's neutral and ground are connected at the genny and then connected with a wire to the bonding system.

Frankly, none of the above seem correct..but, as I said, I may totally misunderstand what he is saying and he didn't mean any of the above.

FWIW, on our NL genny, the neutral wire goes to the neutral buss, the ground wire goes to the ground buss and the genny chassis is connected to the boat's bonding system. This, to me, is "normal" wiring. If the genny ground/neutral is connected directly to the bonding circuit, there are a lot of connections/additional wiring between that connection and the actual ground or neutral buss, all subject to corrosion/failure.

[Pete]

Vincent, it appears that you have two problems, a floating ground at the generator and a wiring/breaker problem. As for the folks that did the installation, I would not invite them back. So lets deal with the grounding first.

If you look at the diagrams you provided with the wiring alternatives, you are wired for 120 volts. So your setup is the left hand column of the three on the wiring diagram. Drop down to the left hand box labelled "schematic". Here you see T1 and T3 tied together going to a breaker and serving as the L1 or hot connector. Next you see T2 and T4 tied together and providing the L0 or neutral wire. As I read your description of the wiring and look at the pictures all of this is correctly done. Now drop down to the next left box labelled "Diagram Grounded Neutral". The next box down is labelled "Diagram Isolated Neutral". The difference between the two is a jumper from the L0 standoff to ground or not. From your picture there is no jumper thus you are wired for a floating neutral. This fix may be as simple as installing that jumper, but someone with electrical skills should definitely double check my conclusions and do any electrical modifications.

The second problem is the 40 amp breaker is definitely too low a rating. Again a person with electrical skills should check the wire size between the generator and the panels in the boat and replace the breaker with one that supports the capability of the wire. It looks like at least #6, perhaps #4 wire so you can at least go to a 50 breaker and perhaps to 70 amps

These two items should get you to a base that will support the installation of your inverter, fix the polarity light, and give you increased electrical capacity when running on the generator.

That is my take of your situation, which is two rather simple fixes.

Pete

[Boatnut]

I also find this thread a bit confusing, but I confuse easily.

A couple of things for what they may be worth.

The 120/240 labeling simply means the generator is capable of producing 120 volts or 240 volts, depending on how it is set up.

When it is set up to produce 120 volts, then the load current is double what is needed on 230 volts. If it is producing 120 volts and you have a 40 amp breaker it is going to trip. I would not suggest jumping the breaker, that would eliminate current protection for the generator, the breaker should be replaced with a breaker with the proper rating. It is possible the generator is set up for 230 volts, and whoever installed it split the load from the generator into 2, 120 volt circuits, the would avoid the need to replace the lower rated breakers.

The reading of neutral to ground of 49 volts and hot to ground of 69 volts is defineately incorrect, indicating a problem with the generator wiring. Note 49 plus 69 equals 118 volts. As you stated this problem started with the installation of a charger inverter, it sounds like somehow the ground and neutral wire were messed with. Perhaps the installer reveresd hot and neutral at the inverter. What is sometimes quite confusing is that mechanical connections and electrical connections are not always physically located in the same place.

In any event, until this problem is resloved you have a dangerous situation being that there is a voltage difference between neutral and the safety ground. Please be careful.

One of my major agrevations with electrical work being done by contractors, is many do not seem to have any respect for standards and codes. They also do not seen to deem it necessary to leave a drawing indicating what they did, so someone else can understand it, when they work on it. Some consider this job security, thinking they will be the only ones who can fix it again. When they do this the next guy has to charge the customer additional time to figure out what the idiot before him did, this can sometimes lead to higher cost for repairs.

Hope this helps, if you have any questions shout out, If I don't the answer I'll tell you so. and will usually find someone who does know. Sometimes the best service guy is the one who knows when he doesn't know. Electricity is a pain in the butt to those who do not work with it, it's even a pain in the butt sometimes when those of us who are supposed to know work on it. LOL

Good luck lets us know what you find, so we all learn.

[Vincentc]

I apologized for any confusion I created.

As shown in post 13, the generator label indicates "as manufactured - 120/240". When you refer to how it is "set up" does that mean how the 4 wires are connected, or is there some internal change made to the generator?

If I read the wiring diagram, the logical way to connect the generator would be to connect the two 120 hot leads, one to each pole of the double pole 40 amp breaker, and then connect one pole to the air conditioner circuit and the other pole to the ship service circuit. Since the breaker on the generator is a double pole 40, that seems to go along with a 120/240 set up.

Regarding the question of whether the inverter install is related to the polarity issue, I do not think it is.

The polarity problem was discovered after the inverter install, but until the install there were no indicators on the boat to reveal the problem. As part of the install, polarity indicator lights were added which indicated the problem which I confirmed with a volt meter.

Polarity is correct when operating on shore power with or without the inverter connected. Polarity is incorrect when taking power from the generator, with the inverter disconnected from all circuits.

Thanks

[SKYCHENEY]

Pete has this correct. It is configured for one 120v service or output right now. If you want to split to two 120v outputs, then you would need to configure it for the 240v setting and run one hot to the A/C panel and the other to the Ships service panel. I don't think that is necessary as you will need to have two selector switches, one for each panel. Leave it as it is with the 120v configuration and just make the two changes that Pete has suggested. That is the easiest and cheapest way to solve the problem.

[Boatnut]

To answer you question about connections, the connections are made at a specified location in the generator, typically a phenalyc boart with terminals, or by tying the wires from the generator together. This is where an owners maunual is invaluable.





I agree that Pete is onto the problem. I do find it interesting that the generator is so large, did Hatteras put 9KW generators on 43's. It sounds like the previous owner may have upsized things a bit. The fact that you have 40 amp breakers suggests either a smaller generator was originally installed, or the boat was wired for 230 somewhere along in it's life. To be properly protected not only does the breaker need to be the correct size, the wire also needs to be the correct size.

You mentioned you have to go to the Genny room to reset the breaker. With one what you have available, you might consider restrapping the generator to 230, and using one 120 leg for ac, and the other 120 leg for the house. This arrangement splits the load, and breaker replacement may not be needed. This is as Sky mentioned not the cheapest way, but it may be the more advantageous way.

The generator wire connected to the 12 volt starter, gets me thinking. Not the way I would think a good electrician would do it.. There should be a ground buss and a neutral buss on board, the generator should be connected at those points. the neutral and ground would be connected together at the generator, but not between the busses. Do not connect the neutral and ground together anywhere on the boat except at the generator, on shore power neutral and ground are connected atthe marina power source.


Electricity will always seek a path to ground, it doesn't care very much which way it goes, it just follows the path of least resistance.

[SKYCHENEY]

Our 1975 43DC came with a 7.5KW Onan.

[Vincentc]

The PO purchased a new generator in 2008, a 9 kW cummins Onan which was installed by the dealer in Bradenton, FL. I bought the boat a few months later and brought it to Mississippi. During the trip home the generator stopped working. I telephoned the dealer, he suggested I contact a dealer in my area. That dealer replaced a controller computer board under warranty, and the generator performed fine since. I do not recall that tech doing anything to check the polarity of the generator output.

In my conversation in 2008 with the FL dealer, he mentioned there was an earlier service call which noted that the generator would not work due to a bad ground.

Yesterday, I checked for continuity between various grounding points on the generator and the grounding buss (green wire) at the main electric panel.

There is continuity between the green buss and the grounding wire on the outside of the generator and between the grounding wires connected inside the generator. There is no continuity with the generator neutral connection.

I am suspicious of the fact that the generator is wired as if it were 120v when the generator is labeled 120/240 75/37.5 amps, and it has a double pole 40 amp breaker to protect it. As shown in post 13, the wiring diagram for the generator shows two output wires attached separately, one to L1 and the other to L2.

I emailed the selling dealer Wednesday and specifically asked if they had reconfigured the generator from 120/240 to 120. No response yet. I also asked about a floating neutral.

There are already two separate 30 amp panels, rotary switches, and wiring back to the generator. The separate wires are combined into one circuit at the boats generator circuit breaker. That combination makes sense for a 120v output generator. Seems like for a 120/240, a second boat breaker should have been added to allow separate 120v circuits from the generator to ship service and air conditioner panels.

I hope To have a capable boat electrician out to the boat soon.

Thanks for the comments