Reverse Polarity with Generator

[Boatnut]

If the polarity indicator is showing. Potential between gnd and neutral there is a chance that the genny and shore power are not wired the same. Its a dumb indicator and will light up with a voltage potential. Neutral and ground should not have potential between them.

Scott, That's what it sounds like to me, if it were my system, I'd tie neutral and gound together at the generator, and see what happens. Being it's not mine, and not seeing the problem, I hesitate to make such a suggestion. I think the safest thing to do is get a qualified electrician to look at it and straighten it out.

What concerns me is the high resistance reading between neutral and ground. A visual inspection should reveal if neutral and ground are connected, it's not too hard, look and see where the wires from LO on the generator go, if they don't go to ground then that's the problem.

I would also confirm that the shore power is grounded properly as well.

 

[Vincentc]

It is difficult to to communicate things I do not really understand. I hope I am learning.

I am still trying to find someone with the expertise and time to come out to the boat and set it up properly. I have contacted several recommended electrician, but so far the closest I have come was a phone conversation with an electrician who kindly reviewed the situation and told me his impressions after looking at photos and my test results. He believes he understands the problem but is committed to other projects for the next few weeks.

He was concerned with the safety hazard, also said that the Neutral and Ground need to be connected at the generator and could not understand why the generator was set up with an isolated neutral.

In addition, I understood him to say that the generator could be wired with two 120v outputs by connecting:

"T1" to one side of the 40 amp double pole breaker on the generator, and attach the Hot wire of one of the 30 amp circuits to the load side of that pole:

"T4" to the other side of the 40 amp double pole breaker on the generator and attach the Hot wire of the other 30 amp circuit to the load side of that pole;

"T2" and "T3" combined and connected to ground at the generator and the Neutral wires for both 30 amp circuits to T2 and T3.

I would need to add a second breaker next to the existing breaker located near the generator (labeled "Generator No. 1) so that I would have separate breakers for each of 30 amp circuits and keep separate L1 and L2.

I am convinced there is no Neutral to Ground connection other than the connection ashore for shore power and the switched neutral ground connection which closes when the inverter is operating. I have conducted the tests using a multimeter recommended by Nigel Calder as well as the tests included with the Blue Sea installation instructions for the breaker panel and rotary switch installed for the inverter and everything is with limits except for the lack of a neutral to ground connection at the generator.

I hope to report soon regarding results of a qualified person looking at and correcting things.

Regards,

 

[Avenger]

I think he's describing wiring the generator for 240V and splitting the legs to get two 120Vs. The only problem with that is if one leg is loaded significantly more than the other i.e. if the Air Conditioning is all on one circuit, it loads the generator poles in an unbalanced manner which does not enhance generator life. If there are no 240V loads on the boat it's best to wire it for 120V operation.

 

[Vincentc]

I can see how the load would not be balanced. Glad you pointed that out. Actually the tech I spoke to did not recomend splitting the load, but answered my question, could it be done that way. Splitting sounded neater to me, but the need for a balanced load makes splitting impractical.

It seems like jumpers on both ends of the double pole 40 amp breaker on the generator would allow the hot wire load to be carried by both poles of the breaker and take care of the tripping breaker problem.

Hope to get someone to the boat soon to set up a neutral to ground connection on the generator and also take care of the breaker issue.

Thanks

 

[Canuck Dennis]

When we replaced my onan 7.5 with a Norpro,, we ran from the Norpro to the existing breaker mounted on the bulkhead, 2 wires from the control box to the breaker,we had to switch one internal wire to another post, this enabled the 120 V. which then fed each panel, I did not see any external wiring to grounds or otherwise.
YMMV

 

[Vincentc]

Dennis,
Did you connect the two green grounding wires to the generator?

Although my grounding wires are connected to the generator, there is no neutral to ground connection at the generator. As I understand it, that connection is required by the ABYC for safety reasons, not functionality.

You may want to check your wiring to see if you have continuity between neutral and ground at the main panel with the panel selector switch turned to "generator". You do this test with the shore power disconnected and the generator and any inverter OFF.

If you do not have continuity, I would be curious to know if you have voltage between the neutral/white wire bus and grounding/green wire bus at the main panel with the generator running and the panel switched to "generator".

Regards

 

[Boatnut]

With reference to Dennis' post and Vincent's comment in his last post. As we all know some contractors will cut cost corners wherever possible. If there truly are no ground wires to any power source, you then have what is often called a floating power source. What these guys do is tie the neutral, and ground together at the power distribution point. There is little doubt in my mind there are lots of boats out there wired this way. Yes it works, the down side of such a set up is there is no safety ground on the generator. Should anythig go wrong with the generator the case of the generator could become hot.

Ground and neutral can be very confusing. Neutral is the return leg to the power source and is a current carrying line, if wired correctly the wire color is white. The green or green wire with a yellow tracer is a safety ground and is not a current carrier. It is there to provide a lower resistance to ground to try and avoid a shock hazzard. A shock is caused because the human body is the path of least resistance, the safety ground hopefully provides a lessor path of resistance.

Not too long ago, I was introduced to a new boater at the marina. He had some work done on the boat and his wife was complaining that she would get a shock in the galley sometimes. At his request I took a look at the situation, and after about 15 minutes of diagnosing, the problem was apparent. The electrician had reversed not and neutral on one of the 120 volt circuits. The gentleman had contacted the guy that did the work, and was told his wife was nuts. Well to make a long storyshort, I have had a few go around with this guy. I went over to his shop with the owner, the guy took one dirty look at me, and then followed us back to the boat, and fixed the problem. So who the heck to people who do not know electriciy protect themsleves, it scares me sometimes.

Happy Boating Everyone,

 

[Canuck Dennis]

The gen set came with it's own frame, perhaps the grounding was internal at the factory during assy. the 120 v wiring was to the best of my memory, identical to the original Hatteras factory wiring of the Onan, the electrician followed the Onan wiring diag. to compare the setup. Do not have an inverter on board.
The electrician was at Owl Creek boat works, so, I assume he was competent.

 

[Vincentc]

I spoke to another Onan generator technician today who confirmed the thoughts expressed here and elsewhere to connect the neutral to the ground at the generator; however, he too was not available to come to the boat, so I went down to the boat this evening and did it myself.

I moved the Neutral wires over to the ground connection, secured everything together and cranked it up. It worked fine, indicated 117.5 volts between the neutral and hot at the generator, and the reverse polarity lights did not light up. I did not have time pull every thingout of the closet and check voltage at the panel.

He suggested I use two jumpers to connect the poles of the double pole 40 amp generator and split the load between the two poles to address the breaker tripping issue. I will probably try that next.

Thanks,

 

[Canuck Dennis]

So, you now have a hot ground ?

 

[Boatnut]

So, you now have a hot ground ?

Good question Dennis. First let's address Vincent's situation. Vincent, you have now established you had a generator wired with an isolated neutral. By moving the neutral to the ground connections you have brought neutral and ground to the same potential. What you did is fine, and has proven the point. It will be better and safer to reconnect the neutrals back where they were, then install a jumper wire of the same rating between the neutral and ground at the generator. This should be the only place neutral and ground should be connected.

Now for dennis' comment. Take a simple electrical device like a toaster. The plug has 3 prongs on it. One prong connected to the black wire, is the hot leg, the second prong is connected to the white wire, and is the neutral. The third prong is connected to ground. Here is the difference between neutral and ground, The current flows from the source down the black wire to the heater element, current passes through the heater element, and returns to the source on the white wire. The green wire is connected to the frame, or case of the toaster, it does not carry current. What this amounts to is if a failure in the toaster should happen, like the heating element breaks off and lays up against the case. Without the green ground wire connected to the case, the case will be hot, probably a potential of 120 volts. If the green wire is connected, you now have a short circuit to ground, which gives a lower resistance to ground than your body if you aren't standing in a pool of water. If the circuit is properly protected by the corrent size fuse or circuit breaker the fuse will open, or the breaker will trip. It is called a safety ground because it is intended to react in a manner that prevents a shock to the operator.

 

[Vincentc]

Dennis, Interesting point, but I don't think so.

As I understand it, a voltmeter should read voltage between hot and neutral and between hot and ground.

Since the generator no longer sets off the red reverse polarity lights and the green lights are on, I assume that there is no voltage between neutral and ground at the panel, but there is between hot and ground.

Shoreside, the neutral and ground are connected at the main panel. The inverter connects neutral and ground at the inverter while inverting. Like Nigel Calder says in his boatowner's manual: " An onboard generator has its neutral and grounding wires tied together at the generator case and nowhere else."

I typed this before seeing Boatnut's post, and would defer to his assessment.

Regards,

 

[Vincentc]

Boatnut,

I prefer better and safer,

How do I determine what is the same what is the "same rating"?

The two "T" generator wires leading to the Neutral post look to me about 8 or 10 ga and the Neutral connected to those wires about 4 or 6 ga.

Thanks

 

[Boatnut]

Vincent sorry for the confusion. I was referring to the wire size, it shoud be at least the same gauge as the hot side, one size larger never hurts.

As I have noted in the past, Calder sometimes leaves a few details out, and things to the unknowing get missed, generators do not come totally prewired and set up for specific situations, it is up to the installer to determine the setup. This is what your problem was, the neutral was not grounded, giving you an isolated neutral. It sounds like you have solved your problem. that's great. Be sure to make a final check for voltage between neutral and ground, don't ever assume with electricity, like you never assume the gun is not loaded.

Have a good day!

 

[Vincentc]

Thanks for your review and advice.

Good analogy.

Regards,

 

[Boatsb]

Vincent sorry for the confusion. I was referring to the wire size, it shoud be at least the same gauge as the hot side, one size larger never hurts.

As I have noted in the past, Calder sometimes leaves a few details out, and things to the unknowing get missed, generators do not come totally prewired and set up for specific situations, it is up to the installer to determine the setup. This is what your problem was, the neutral was not grounded, giving you an isolated neutral. It sounds like you have solved your problem. that's great. Be sure to make a final check for voltage between neutral and ground, don't ever assume with electricity, like you never assume the gun is not loaded.

Have a good day!

Every gun is loaded.

 

[Vincentc]

I checked voltage from the generator at the main panel. 118 volts between hot and neutral and between hot and the ac ground bus. Less than 0.1 volts between the neutral and the ground.

Making a neutral to ground connection at the generator fixed the polarity issue.

Thanks for the help.