Inverter install - Reverse Polarity??

[senormechanico]

I'd try a small 12 volt light from neutral to ground with the voltmeter hooked across it as well. If it doesn't light or burn out, I'll bet you could clamp it.

[capn_billl]

I've had the reverse polarity come on with my inverter twice. The first time I had a power glitch just as the fridge compressor was starting, and it fried the transfer relay leaving one leg permanently welded to the inverter when the shore power came back on. (rare event).

The second time I disconnected the inverter and still got it, this was on an electrical system that had worked flawlessly for years. By using a meter I found a corroded wire that was a neutral where power came into the boat, the corrosion caused the neutral to float above ground enough to trip the reverse polarity sensor, and cleaning the connection caused it to go away. (one symptom was with every thing turned off ,no alarm, but as I turned on devices one by one it tripped at about 5 amps of draw).

Another time I had just moved my boat and plugged into a new dock, I didn't get the reverse polarity alarm with only one plug connected, (I use twin 30 amp), but with both, I imediately got it even with all breakers off. A meter showed one of the marina outlets was wired backwards. After argueing with the harbermaster for weeks, (he said a licensed electrician said it was OK), I MOVED THE BOAT. So if your in my old dock be aware.

[goboatingnow]

The OPs problem are simple, The inverter is a AC power source, hence its neutral and AC earth ( ground) wire should be connected when the inverter is in circuit and shore power is not. The transfer switch or the inverter should provide a inverter neutral/earth link ( relay) to accommodate this . In its absence, the inverter neutral is floating above the earth. ( common mode voltage) , typically its not dangerous as only leakage currents can flow, but these are typically enough to support a neon.

without that connection, when the invertor goes live and a live fault develops that say makes an outer case go hot, the ground does nothing ( even though you cant get a shock anyway, as there no ground return path to put you in the circuit. Of course you will get a shock if the case is hot and you manage to touch it and the neutral to the invertor!.. Still following me!

dave

[FlyingCloud1937]

Originally Posted by goboatingnow

The OPs problem are simple, The inverter is a AC power source, hence its neutral and AC earth ( ground) wire should be connected when the inverter is in circuit and shore power is not. The transfer switch or the inverter should provide a inverter neutral/earth link ( relay) to accommodate this . In its absence, the inverter neutral is floating above the earth. ( common mode voltage) , typically its not dangerous as only leakage currents can flow, but these are typically enough to support a neon.

without that connection, when the invertor goes live and a live fault develops that say makes an outer case go hot, the ground does nothing ( even though you cant get a shock anyway, as there no ground return path to put you in the circuit. Of course you will get a shock if the case is hot and you manage to touch it and the neutral to the invertor!.. Still following me!

dave

You are correct, on the inverter becoming the power source once the shore power is disconnected, thus requiring the neutral to ground switching relay I posted above. Same goes for a generator that isn't ground switched, which many are not.

All Marine inverters are required the N-G-S, but there are many inverters pressed into marine service, that lack this, so the solution is the link I posted above.

Now the problem with the floating neutral comes when a fault or current is flowing on the floating neutral, which could energize any case that is not grounded. Then a person makes contact with the floating neutral, and also manages to make contact with something grounded to ships ground...now that person become the path to ground, and death may ensue. Guess what it has happened on many occasions, and that's why the requirement of the N-G-switch.

Also the output breaker of the inverter will not trip minus the N-G-S. As the only way to kill the inverter when in inverter mode, is a dc disconnect it won't stop the floating hazard, but it will alert the owner to the fault so that it may be cured before death.

Lloyd

[Stu Jackson]

This is not an answer to the OP question (although we do not get the OK polarity light to come on when our Freedom 15 I/C is powered - we have two lights: one OK polarity, the other RP).

My question to the OP is why bother with the added complexity of an automatic switch? Why not just a manual switch like a Blue Sea 8032? Or perhaps I'm misunderstanding the automatic part, where a manual switch "automatically" switches between one source or the other.

Reason I ask is, as suggested earlier by one skipper, if the charger is on and/or the water heater is on and shorepower dies for any reason, the OP is gonna have a dead house bank real soon.

So help me understand what you mean by "automatic transfer switch."

Thanks,

Stu

[Jon4399]

Stu, guess I didn't think things through completely when I bought the parts. I had crewed on another boat that had an auto transfer switch, so everything was handled automatically. But on mine, I think I need to physically turn on the inverter anyway. I don't see the need to run the thing when on shore power or when I don't need 120v power. Had I though things through, a manual transfer switch located next to the inverter could have worked as well.

[mitiempo]

A separate transfer switch should not be needed. The inverter has an automatic transfer switch built in. The normal way to wire one is shorepower to main breaker then to inverter then to load breakers for the circuits the inverter is to power. When on shorepower the inverter charges (assuming it is also a charger) and automatically switches to inverter when the shorepower is unplugged. There is no need to complicate things more than necessary.

Exactly which model of inverter is it?

[Jon4399]

The inverter is an AccurateTools 1500w pure sine wave model. The approach suggested by mitiempo only applies to charger/inverter combinations. The one I installed is only an inverter, so only has 12v inputs. The ground is floating, with about 17 volts registering between the neutral and ground. This is enough to light the reverse polarity lamp. But when I tested it through the auto transfer switch, I only turned off the breaker at the dock pedestal. It seems to me that this would have left the dock ground connected, and shorted the inverter's ground to true earth ground. I was worried that clampint the neutral to ground could fry the inverter, but wouldn't shorting the inverter's ground (17 volts) to earth also potentially fry the inverter?

Secondly, what damage or risk would be presented if the shore power cable were removed, severing the earth ground from the circuit, and using the inverter with the reverse polarity lamp lit? The entire circuit would be contained within the inverter to electric panel to outlets? Thinking about the boat's wiring, I can't see any risk or potential damage. Any "experts" out there still following this thread?

[Jon4399]

I'm sorry, but I forgot to mention that the boat has a "zinc saver" installed, which is wired on the shore power ground circuit. Perhaps that cut the earth ground from the circuit preventing damage to the inverter when I turned it on. Do boats have a hull ground (through hull) connected to the electric panel ground?

[mitiempo]

The "zinc saver" is a galvanic isolator. It has a diode array that prevents about 1.2 volts from travelling from the boat to the dock through the ground wire - most corrosion is caused by a current of less than one volt. If there is a fault it will pass the galvanic isolator.

Boats should have the AC ground connected in the same location as the DC ground, per ABYC, usually the negative bus.

Marine inverters, like the Xantrex Pro series, have AC input as well as inverter outout and do have an automatic transfer switch built in, whether they are inverters only or inverter/chargers.

[Andina Marie]

Electrical regulations require the neutral and ground to be joined together at the SOURCE of power and never at the load.

When on shore power the source point is the main transformer supplying the dock so there should be no connection between ground and neutral on the boat.

When you are on the inverter, however, the source point is the inverter so ONLY when the inveter is running should the ground and neutral be connected together on a boat. Many modern inverters have a relay that is operated when the inverter is running that connects neutral and ground automatically. If your inverter does not have this, you should add it for SAFETY reasons and to stop the reverse polarity light coming on.

[Jinxer]

I did a general search for my problem and this forum came up... and I notice that this forum speaks mainly about Boats etc... however, I am hoping that my inverter problem and the solution is more of a general inverter situation.

Anyways, I installed a bunch of Solar Panels... for the sole purpose of being able to power my furnace in the even of a power outtage. So I plug the panels/battery into the inverter and then into my furnace... and it wont start and tells me there is a REVERSED POLARITY issue. Now even tho I have read thru these threads, it seems as if noone has actually layed out why it does this and more importantly what steps need to be done to fix the problem. In the previous post it was suggested that I hook the neutral to ground.. so even tho I new that should not work, and infact fully expected it to ruin my inverter I still tried it anyways, only because I have tried every thing else and noone can seem to give me any answers.. and sure enough the moment I plugged it in.. it started to sizzle and blew all 3 fuses. I replaced the fuses and ofcourse undone the fround to neutral and plugged it in.. and it blew the fuses again.. so I can only assume that the inverter is now just toast.

ANYWAYS.. is there anyone that can explain in laymans terms how to overcome the reversed polarity issue so I can run my furnace?

Thank you!

[hellosailor]

Jinxer the forum comments on this are specific to boats, not land-based homes, as the AC wiring and 'ground' are quite different in the two situations.

Is your furnace an actual land-based home electrical heating system? Or are you talking about a marine installation on a boat?

And what equipment is telling you it has reverse polarity?

Is this a 120/110 VAC system or a 220/240 system?

[Jinxer]

Yes it is a land based home furnace. And its the furnace itself that is saying that the polarity is reversed. I checked the output from the inverter and it is giving the correct electric.. but the furnace is saying reversed polarity. And its 110. I know this isnt a boat situation But maybe you have a solution for me anyways?

[s/v Jedi]

Originally Posted by Jinxer

Yes it is a land based home furnace. And its the furnace itself that is saying that the polarity is reversed. I checked the output from the inverter and it is giving the correct electric.. but the furnace is saying reversed polarity. And its 110. I know this isnt a boat situation But maybe you have a solution for me anyways?

Ground the inverter.

ciao!
Nick.