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Old 26-05-2009, 06:53   #1
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Reverse Polarity

Hi all,

I have a 2007 Sea Ray 240 Sundancer US model. I live in Europe and it is fitted with a 220V-110V stepdown transformer for the shore power.
I just bought the boat, and when I tested the shore power while the boat was sitting on the trailer, everything was working fine.

Now the boat is in the water and the Reverse Polarity light is on. I have tested the shore power, and it is indicating normal, with a hot a neutral and ground with zero volts between null and ground.

I have not changed anything on the boat.

The light comes on whenever shorepower is connected, before anything is turned on on the main breaker panel. Even the "shore power" switch is off. When I turn on the shore power, the voltage indicated is only 100V.

I have measured the secondary side of the transformer, and it measures 110v between hot and neutral, 110V between hot and ground but 220v between neutral and ground. This is while the transformer has been connected. I cannot disconnect the 110V side without cutting the wires, but that might be the next step...

I have tried to rotate the power cord to change polarity, without any result.

Anybody with any suggestions?

Thanks in advance,
Martin
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Old 26-05-2009, 07:42   #2
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RPI’s are wired in series with a (minimum) 25,000 Ohm resistor (unless they utilize a momentary contact “push-to-test” button), to prevent a path for stray currents via the grounded Neutral wire.

When high amperage loads are operated in the circuit, enough voltage drop in the length of the Neutral wire can be created to overcome the resistance in the 25K resistor, that sufficient current is driven through the LED to cause faint illumination.

This situation is not inherently dangerous; however, it can indicate undersized wiring in the dock, shore power cord, or boat’s AC wiring.
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Old 26-05-2009, 07:52   #3
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Read this discussion to get some background

Reverse Polarity Indicator.
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Old 26-05-2009, 13:07   #4
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Thanks for the quick replies.

I had infact read the thread on RP before posting this one, and tried to ground it like on the diagram, thereby tripping my GFI.
The shore power ground and boat ground are both wired to the core of the transformer. All this could indicate that I have an autotransformer, and then what?

Two things I don't get:

One: It worked at home without RP light. It was connected to a wall socket without ground. Now in the water the RP lights up (NOT a faint light...) both with and without ground connected.

Two: The voltage on the meter on the main breaker panel only indicates 100V, whereas my voltmeter (when connected directly to the output of the transformer) indicates 110V. The input current is at 220V.

The only "component" between the transformer and the RP light is (as far as i know) a galvanic isolator. Can that be the problem?

Martin
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Old 26-05-2009, 13:13   #5
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I am 99% sure that this is the exact transformer that I have in my boat

220V-240V to 110V-120V STEP DOWN TRANSFORMER 5000W for sale - TradeMe.co.nz - New Zealand

(if that helps..)

last: Can the RP light be because of a failed component? (still bearing in mind that the light is on when all main breakers are off)
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Old 28-05-2009, 11:15   #6
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You do have an autotransformer according to the website you cited, and the RP light is showing one or more improper connections. I am assuming that the RP light was installed with the original 110v wiring. I am about 80% sure that the voltages you measured are the result of reversing the load and neutral wires on the input (220v) side of the autotransformer. That would put the neutral on both sides at 220v above ground, and the load side of the output at 110v above ground.

The reason you did not see the RP light on the trailer is that the AC ground wire connection to the 110v circuit may have not been made, and there is now a ground connection to the water, probably through the DC system.

My advice is not to use the dock power until you fix things so that you don't get the 220v from neutral to ground, especially if your boat is in fresh water.
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Old 28-05-2009, 11:48   #7
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The RP light was as you assume factory installed and has not been tampered with. The only modification to the electrical system is the 220v/110v transformer, so regarding improper connections my only guess is either a failed component or a bad transformer.

I have tried to flip the plug on the input side several times (it's a standard schuko - reversable with ground on both sides) but the light did not go out.

I will try once more tomorrow to flip the plug and measure the voltages and see if the 220v between ground and neutral remains.

Will an isolation transformer help the situation?

I am with you on not using shore power until it is fixed, but I have yet to find an electrician who is up to the task. So far, I seem to know a whole lot more about this issue than the "professionals" I have been in contact with, so my big problem is: What do I do to fix it?

The boat is in salt water.

Thanks for the help so far /Martin
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Old 28-05-2009, 13:07   #8
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Good luck with it--I wish I could send you the diagram I just drew, but I'm traveling. I would note that the neutrals on both sides of an autotransformer are connected, so that if the load and neutral are reversed on the input side, (1) you should also see 220v from neutral to ground on the input side and (2) trying to bond the neutral output to the ground will result in a quick overcurrent trip of your dockside breaker.
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Old 29-05-2009, 05:00   #9
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Hi,

First of all: Problem fixed!!!

I measured the voltages as you described, and yes, the voltage between neutral and ground went to zero when the plug was flipped around. The only problem was that I had done this about a hundred times before and the RP light was still on. I tried to reference the boat's ground as well as the shore ground with the same result.

So: how can the light still be on when my voltmeter tells me that everything is fine (110V between hot and neutral and 0 between neutral and ground)

Answer: The guy who installed the autotransformer switched the wires on the secondary side obviously making the RP light come on regardless of polarity as it would sense either 110V or 220V between "neutral" and ground.
So, I cut the wires on the secondary side, switched them around and now the light is off.

Thanks for the excellent advice. If you're ever in Denmark send me a message and I'll buy you a beer.

BR
Martin
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Old 29-05-2009, 11:35   #10
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Congratulations!

Now that you have sorted out the internal wiring, the only thing left to do is hook up a 220v RP light between the ground and neutral on the input side of the transformer. If your original RP light is 110v and you want to use it, you could put a series resistor in the circuit, I would guess something about 30k ohms would work for an incandescent light.
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Old 12-07-2012, 23:22   #11
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Re: Reverse Polarity

I have the same Sea Ray in Australia and I am having the same problem getting the transformer to function. Please explain which wires you switched on the secondary side of the transformer?
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