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Old 14-12-2011, 11:25   #1
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Unhappy Inverter install - Reverse Polarity??

I've just completed the installation of a 2000W sine wave inverter and separate automatic transfer switch. I figured it should be a straightforward installation. I simply wired in the auto transfer switch between the shore power connection and the electrical panel. Then installed the inverter and ran a heavy gauge chord from the inverter to the auto transfer switch. I set the transfer switch to immediately transfer when shore power is disconnected (The switch came with a 30 sec. delay for generator start-up.) There is a common ground strap in the transfer switch, and the house ground which previously went to the shore power receptical was terminated there, along with the ground from the shore power plug and the ground from the inverter.

When I turned on the inverter (shore power disconnected), the inverter registered 425W drain (??) and after a minute or so, the electrical panel reverse polarity light came on. Since the electrical 120v breaker is turned off, I presume the transfer switch is drawing that much power, which seems a lot. Also, why is the reverse polarity light on? The only thing I can think of is to disconnect the inverter ground from the transfer switch ground strap. Can some smart electrical engineering guys offer suggestions as to why, and how to fix it? I learn so much from this forum. Here's hoping this time too.
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Old 14-12-2011, 12:01   #2
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Are you sure theres no load connected that the obvious answer. Also you mention a generator. Is it in circuit as well ( even if off). The reverse polarity light could be that you just have the invertor live an neutral crossed

Dave
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Old 14-12-2011, 13:04   #3
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Re: Inverter install - Reverse Polarity??

"the electrical panel reverse polarity light came on."
Shame on me for repeatedly forgetting the details, but this is common with inverters and generators on boats where there is no true "ground" and often means one piece of equipment or the other is getting confused by neutral being used as (wired to) ground on the other.
Check the neutral and ground connections, installation instructions for kludging the lack of an earth ground. Or a web search might find one of the complete answers from past threads.
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Old 14-12-2011, 13:08   #4
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Re: Inverter install - Reverse Polarity??

i often forget to turn off my hot water when using the inverter uses tons of power
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Old 14-12-2011, 13:30   #5
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Re: Inverter install - Reverse Polarity??

Well, in answer to a couple of the comments, there is no generator on the boat. ( I have a Honda portable which I can use via the shore power plug.) And, the ac master switch on the electric panel is turned off.).

The wiring from the boat's electric panel is black, white and green. The leads on the transfer switch are black white in from mains; black white in from generator (inverter in my case); black white out to electric panel. I reconnected all blacks to blacks, white to whites, and greens to greens. The common point is the transfer switch, which has a buss bar for the grounds (green). What happens if I disconnect the green ground from the transfer switch? Also, since it is ac, is there any difference between black and white?
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Old 14-12-2011, 14:55   #6
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Re: Inverter install - Reverse Polarity??

Could be the shore power charger is on???
Makes a nice circle of electricity.
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Old 14-12-2011, 15:15   #7
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Re: Inverter install - Reverse Polarity??

Quote:
Originally Posted by Jon4399 View Post
.......What happens if I disconnect the green ground from the transfer switch? Also, since it is ac, is there any difference between black and white?
Do NOT disconnect the green (grounding) wire on the AC shore power circuit. This should always be present when the boat is plugged into shore power, as a safety requirement.

Yes, there is a difference between black and white in an AC circuit. You can measure 120VAC from black (hot) to green (grounding) as well as from black to white (neutral). There should be very little difference in potential between the white and green wires. Polarity is important, and failure to respect it can cause problems and, in an extreme situation, can kill you.

Bill
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Old 14-12-2011, 17:46   #8
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Re: Inverter install - Reverse Polarity??

I disconnected the green ground wire from the inverter to the transfer switch. I left the ground wiring between the shore power plug and the transfer switch intact, as well as the ground from the main elec. panel to the transfer switch. Unfortunately, disconnecting the ground between the inverter and the ground buss on the transfer switch had no effect. The reverse polarity lamp still came on. It now seems to me that the polarity of the current comming from the inverter is backwards to that of the boat. I understand that there should be little or no difference in potential between the neutral and ground. Doesn't that mean then, that if power for the main panel is comming from the inverter to the master panel, that there must be a significant differential between the inverter's neutral and ground? I guess I can test it with a multi-meter. What would be the effect of my reversing the primary and neutral connections comming from the inverter to the transfer switch? In other words, connect the inverter black to the white input of the transfer switch, and white to black? The transfer switch directly connects the wiring from the inverter to the main elec. panel, so if the panel says the current wiring is polarity reversed, then reversing them could fix the problem. No? If that doesn't work, I don't know what will.
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Old 14-12-2011, 18:04   #9
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Re: Inverter install - Reverse Polarity??

Measure the voltage between the white and green wires when you have the inverter on and the shore power disconnected. If its the same as between the white and black wires, then you may have true reverse polarity. If its lower you may have a floating ground on the inverter. Read the inverter manual carefully about the green wire--my inverter/charger has an internal transfer switch-- it makes an internal connection between the green and white wires only if it does not detect dock power.



I assume you sorted out the 425 watt load issue--was it the charger or the water heater?
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Old 14-12-2011, 18:20   #10
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Re: Inverter install - Reverse Polarity??

Jon,
Reverse polarity is when the hot and neutral are reversed. To correct it just swap the white and black from the inverter to the transfer switch and it should correct the problem.
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Old 14-12-2011, 19:33   #11
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Re: Inverter install - Reverse Polarity??

I had a similar/related problem on my boat when I installed a Xantrex 2000 pure sine wave inverter. I don't remember how I detected it, but there was a problem with the polarity somewhere.

It turns out that the shore power plug was wired incorrectly. That's right, I owned the boat for 2.5 years and all that time the entire boat had reverse polarity. It was an easy fix once I figured out what was wrong.

Maybe you have a simlar problem and your reverse polarity indicator is also wired wrong?

Regards,
Brad

P.S. A pure sine wave inverter is good to have. At 2000 watts we have a 5000 watt peak for a certain number of seconds. It easily drives a microwave. I highly recomend getting a battery monitor, so you can watch your percent charge drop as you cook things.
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Old 14-12-2011, 20:21   #12
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Re: Inverter install - Reverse Polarity??

Jon, You did not say what type of inverter you installed. Many RV inverters are not made to be used on a boat and will give a reverse polarity light even when wired correctly because the inverter is looking for different type of ground and neutral than your boat provides. I would suggest you contact the inverter manufacturer for some tech support before you try a lot of things that won't fix the problem. Here is some additional information on false reverse polarity, AC Reverse Polarity False Indicators . Chuck
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Old 15-12-2011, 01:03   #13
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Re: Inverter install - Reverse Polarity??

You'll find your answer here voltage on the neutral of a trace sw inverter

This sounds like a Xatrex unit.
If it doesn't have a built in Neutral to ground switch, and the the neutral is floating, there will be enough ghost voltage to light the RPL.

Lloyd

Quote
FAQs
Power Inverters


Voltage measurement issues (AC output)

I've installed the modified sine wave inverter and it's working okay. However, the output voltage doesn't seem right. There is 124 vac between the hot and neutral pins but the safety ground is not at 0 volts with respect to the neutral pin. Instead, the safety ground appears to float about halfway between the neutral and hot pin voltage. Please explain what's going on!

This FAQ applies to Xpower, PROwatt, Portawattz, Jazz and Xantrex inverters, including the inverters integral to Powerpacks.

Your inverter is designed to have loads plugged directly into it and not be permanently connected to an AC distribution system. The fact that the inverter is not a permanent installation means the US NEC (United States National Electrical Code) doesn't apply, and the NEC is the main place where the requirement resides for single-phase 120Vac or 240Vac systems to have neutral bonded to earth. The US standard for inverters of this sort, UL458, does not have a requirement for a bonded neutral on the output of inverters.

Regarding the voltage that the you are measuring, the ground does not float halfway, rather the neutral is not at 0 volts. The grounding is correct, in that loads plugged in will have their chassis held at the same ground potential as the chassis of the inverter, but the neutral has approximately 60V on it instead of the usual 0V. The impact of that is minimal, since wiring and equipment connected to the neutral side of the circuit are required by safety standards to be treated as if they were at 120Vac. This is because there are many receptacles that are wired backwards or 2-prong plugs that are not polarized. As a result the 60V neutral is not accessible to the user, and any shock hazard presented is mitigated by lack of access.

The main safety agencies, CSA, UL, and ETL, have all approved inverters with this half-voltage on the neutral scheme, and the manuals contain warnings not to AC hardwire any of these inverters.
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Old 15-12-2011, 01:18   #14
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Re: Inverter install - Reverse Polarity??

Here is the Relay and the cover for the relay. This is a pic schematic.

Lloyd

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Old 16-12-2011, 09:08   #15
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Re: Inverter install - Reverse Polarity??

I think don had the right answer. I put a meter on the inverter output. It registered 17.2 volts between neutral and ground. It measured something like 126 volts between hot and neutral. I have sent a note off to the distributor, asking for a manual or instructions re grounding. I am not sure I can clamp the neutral to ground without frying the thing. Perhaps is just won't work and I'll have to get one more suited to the marine installation. Live and learn, but thanks to everyone for their comments and suggestions. You guys are GREAT!!!
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