Reverse Polarity at Panel Only

[crayiii]

We just plugged in to (50 amp)shore power in The Bahamas and the reverse polarity light on our panel is bright red. I plugged a tester into all of our AC outlets and they all test okay. I’ve tried a different pedestal and it’s all the same. We are at the end of a finger slip with several very large boats all plugged in.

What could cause this? We were plugged in several places in Florida and it was all okay.

[BillKny]

Originally Posted by crayiii

We just plugged in to (50 amp)shore power in The Bahamas and the reverse polarity light on our panel is bright red. I plugged a tester into all of our AC outlets and they all test okay. I’ve tried a different pedestal and it’s all the same. We are at the end of a finger slip with several very large boats all plugged in.

What could cause this? We were plugged in several places in Florida and it was all okay.

Reverse polarity light come one when there is significant voltage difference between the neutral and ground wires. This can be caused by actual reverse polarity, or by a high resistance in the neutral wire, and then lots of power draw on the lines (i.e. several large boats!). You're portable circuit tester is likely to just be less sensitive to this.

If you have a multimeter aboard, test the voltage between the neutral wire and ground. If you see 120V (or close) that is reverse polarity, if you see less than 5 volts, that would be normal. Anything more than 5 volts or so would be a troublesome wiring system in the marina.

[crayiii]

Originally Posted by BillKny

Reverse polarity light come one when there is significant voltage difference between the neutral and ground wires. This can be caused by actual reverse polarity, or by a high resistance in the neutral wire, and then lots of power draw on the lines (i.e. several large boats!). You're portable circuit tester is likely to just be less sensitive to this.

If you have a multimeter aboard, test the voltage between the neutral wire and ground. If you see 120V (or close) that is reverse polarity, if you see less than 5 volts, that would be normal. Anything more than 5 volts or so would be a troublesome wiring system in the marina.

There is 1v between neutral and ground at the outlet. With this info, what could cause the panel to have a bright red reverse polarity light?

[boatpoker]

Originally Posted by crayiii

There is 1v between neutral and ground at the outlet. With this info, what could cause the panel to have a bright red reverse polarity light?

What are the ohms between neutral and ground

[crayiii]

[QUOTE=boatpoker;3331231]What are the ohms between neutral and ground[/QUOTE

The dock master came by and tested the outlet and said it was fine and left.

I wanted to test my cable so I unplugged it at both ends and tested continuity between all 4 contacts and got nothing.

I then plugged it into the pedestal but kept the breaker off and tested continuity at the end of my cable. I got continuity between ground and neutral and between hot and neutral.

[boatpoker]

[QUOTE=crayiii;3331311]

Originally Posted by boatpoker

What are the ohms between neutral and ground[/QUOTE

The dock master came by and tested the outlet and said it was fine and left.

I wanted to test my cable so I unplugged it at both ends and tested continuity between all 4 contacts and got nothing.

I then plugged it into the pedestal but kept the breaker off and tested continuity at the end of my cable. I got continuity between ground and neutral and between hot and neutral.

There should be no continuity between ground and neutral.

[crayiii]

[QUOTE=boatpoker;3331347]

Originally Posted by crayiii

There should be no continuity between ground and neutral (or hot).

Yeah, I packed my cable up and will continue to live off solar and wind and won't worry about hot water.

The pedestal is a bit corroded and like I said there are several boats on this dock plugged into 100amps, one is plugged into two 100 amps and one has some type of box on the dock between the pedestal and the boat. I'll skip AC power for now.

[ebs001]

[QUOTE=boatpoker;3331347]

Originally Posted by crayiii

There should be no continuity between ground and neutral.

The neutral is the grounded conductor and there should be continuity when the cable is plugged into the pedestal. There should not be any continuity between the hot and the neutral. Did you try checking the pedestal outlet to see if you were getting continuity between the hot and neutral with the breaker off?

If you have reverse polarity from the pedestal the reverse polarity light should come on on your panel even if the pedestal breaker is turned off. Neutrals are never switched.

[BruceS]

""Neutrals are never switched.""
Except in maybe Australia?

[BillKny]

GROUNDS are not switched, but Neutrals most certainly can be!

But in this case, NOT. There is a double pole breaker at the pedistal, which on a 50AMP 120/240 supply shuts off the TWO hots. The neutral and ground SHOULD be connected at the marina power panel, and SHOULD show continuity. If not, you would not have a functioning safety ground.

But this is the case of asking a complex question on the internet. People who do not know the details of the situation are happy to post an answer and with AC power especially that can be dangerous.

Lots of things could be wrong, and giving specific advice without actually knowing all the details is foolish.

[smac999]

if you actually had reverse politary on a 240v boat you'd know pretty soon. smoke would be pouring out of half your appliances. as half the panel would now be running 240v instead of 120v. and the other half the 120v stuff would still be 120v but in rev pol... hopefully breakers would blow before stuff caught on fire...

if you feel like plugging back in. with the main breaker off measure the voltage between all 4 wires in every pair combo before the main it should be easy to tell what's going on.

should be:

red to black 240
red to white 120
black to white 120
white to green 0
black to green 120
red to green 120

you can also measure right at the wires for the rev pol light too to see what's going on. it should still have power with the main breaker off.

[NakedCity]

I also suggest you look at the reverse polarity light wiring itself behind your panel. I once had a situation where a little overcurrent wire melting behind the panel cause the reverse polarity light to come on.

[sinnerman]

There is also supposed to be a small resistor in line with the lamp to prevent stray voltages from erroneously illuminating it.

My internet search for the resistor size came up with the following blog, which also has some good comments / troubleshooting info:

The Marine Installer's Rant: The reverse polarity light AC leaking musing