Help, "Reverse Polarity" Light On!

Pat Anderson

OK, Daydream is sitting in the driveway here at Birch Bay (I am actually typing from the dinette table, folks are still asleep in the house). The shore power is plugged in, same cable I have always used. On the switch panel under the dinette that controls the 120v circuits (outlets, water heater, fridge, battery charger), the main switch is a double puppy (technical term, I know), and one of the lights is the reverse polarity indicator, which is lit red. All the other lights on the panel are on too, green, and everything seems to work. The 12v circuits seem to be working fine. So what is going on here? Nothing got changed...do I need to be worried?

Sea Wolf · Posted: Sat Jul 21, 2007 9:58 am Post subject:

Pat-

This is not something I'm an expert in, but I'd first try the following:

Unplug and plug back in all the connections between the boat and the source and see what happens. I'm thinking you might have a open ground.

Will start reading "Blue Seas" website momentarily. Joe.

On Edit: I think Don is probably more correct (below), but I'll still do some reading.

Sneaks · Posted: Sat Jul 21, 2007 9:59 am Post subject:

Pat is this the first time you've plugged into a circuit at Birch Bay? If so, is it the same extension cord into the same outlet? If you've not had a reverse polarity light before, the most likely source is a miswired extension cord or your house wiring to the convenience outlet is reversed. I would be inclined to think it was the latter not the former, but ya never know. Some of those "Beach Cottages" of that era do suffer from "Creative Wiring" since wiring with a ground connection was unheard of back then.

Don

P.S. Thanks for the dog fix and the warm Birch Bay welcome. Both were appreciated, made even more so by the fact that you're "family." Laughing

Pat Anderson · Posted: Sat Jul 21, 2007 10:11 am Post subject:

Thanks for the thoughts, Joe and Don. I have plugged in here many times before, although I cannot say for sure whether I ever checked whether the polarity light was on or not - I have to suspect the house wiring too. So I gather it is not something that is going to destroy anything?

Don - it was great meeting my uncle! Baxter and I are glad you were able to buzz on up!

Sea Wolf · Posted: Sat Jul 21, 2007 10:17 am Post subject:

Pat-

My Owner's Manual for the Sea Ray says that if the polarity is actually reversed, the main circuit breaker will trip.

More information:

"Typically the REVERSE POLARITY indicator in a boat 115-VAC system is wired between the NEUTRAL and GROUND conductors. If the source of external 115-VAC power is incorrectly wired and has reversed the LINE and NEUTRAL conductors, it will present a voltage of 115-VAC between the NEUTRAL and GROUND conductors on the vessel. This is detected and signaled by the REVERSE POLARITY indicator to alert the vessel electrician that there is a problem with the shore power.
You may have lost shore power due to a circuit breaker tripping, possible a ground-fault interrupter (GFI). In a normal circuit, there should be no current flowing on the safety ground portion of the circuit. If there is a polarity reversal, some current will flow on the ground, perhaps just the current from the polarity reversal indicator mentioned above. This current may be enough to trip off the GFI and interrupt the boat's power.

It is difficult to determine why a particular circuit functioned properly in the past but does not at the present. There may be unanticipated effects from the connection of other vessels to the power distribution. I would contact the wharfinger and ask them to have their electrician verify the wiring of the circuit to which you are connecting."

Source HERE

Joe.

Sea Wolf · Posted: Sat Jul 21, 2007 12:07 pm Post subject:

Pat and anyone else interested:

If the quote above is a bit fuzzy in meaning to anyone, I'll try to make more sense of it.

There are three wires on a 120 volt AC (alternating current) circuit or line.

One wire, typically black in color, is the hot wire and supplies the power which is returned on the second wire, which is the common wire, which is typically white in color. When combined with the hot wire, the two produce a current which alternates in direction 60 times a second at 110-125 volts or so. The common is really the return wire for the hot wire's current.

There is a third wire, the ground, which is literally grounded to the earth in any number of places, such as at a metal stake where the power enters the residence and back all the way to the generators (alternators, really).

The ground is there so that any short in the hot wire to any object will allow the resulting current to pass back to the source through the ground without leaving a "hot" or charged object that could shock someone who came between the hot object and a return path to the source. We ground conduits, appliances, water pipes, and so forth so that they cannot become hot sources for electrocution through a shorting of the hot wire.

Now when you look at a female wall outlet, you see three plug inserts.

The "U" shaped one is the ground. There are two blade inserts. The wide one is the common (return) (white wire), and the narrow one the hot (black) wire.

So how do you check for correct polarity, knowing the above?

If you take a digital multi-meter (almost essential for boat electrical work), you can do the following:

1. Set the meter to AC Volts. Put the probes* across the two blade terminals.
You should get 110-125 volts. (If it's less than 105 volts, don't use your appliances, as they will draw too much current in absence of adequate voltage and may overheat.)

2. Now put the probes in the narrow blade slot (*hot wire) and the ground "U".
You should get a voltage reading. If the ground is good, it should be very much the same as the voltage in #1. Proceed to #3.

3. Now places the probes across the wide blade (common/return) slot and the ground. There should be no voltage.

If you had good voltage, and that voltage was also between the narrow blade and the ground, you have adequate voltage and the polarity is correct.

If you had good voltage, but no voltage betweeen the narrow blade and the ground (and good voltage between the wide blade and the ground), your polarity is reversed.

If the voltage is low, or the polarity is reversed, unplug and call an electrician!

Now perhaps, the quote above will make more sense:

"Typically the REVERSE POLARITY indicator in a boat 115-VAC system is wired between the NEUTRAL and GROUND conductors. If the source of external 115-VAC power is incorrectly wired and has reversed the LINE and NEUTRAL conductors, it will present a voltage of 115-VAC between the NEUTRAL and GROUND conductors on the vessel. This is detected and signaled by the REVERSE POLARITY indicator to alert the vessel electrician that there is a problem with the shore power."

Joe. Teeth

* for AC circuits, it doesn't matter which color probe goes into which terminal
or conductor.

AstoriaDave · Posted: Sat Jul 21, 2007 12:51 pm Post subject:

Very clear. Sea Wolf. Can't stop an old teacher from teaching ... Wink

thataway · Posted: Sat Jul 21, 2007 6:50 pm Post subject:

I would make the assumption that the house wiring--either at the "plug" or it is possiable that the entire house is misswired with the hot and neutral reversed. I always carry one of the little plug into the 15 amp socket polarity testers. (also called recpetical test kits) The LED's in these will help to diagnose the situation if the neutral and hot are switched, or if the neutral and hot are switched. Also taking a volt meter set on 200 volt AC range, and check the voltage between the neutral and ground--there should be zero--or at least less than 3 volts on this leg. If there is 110 volts then the neutral and hot are reversed. Another device which is very good to have on the boat is the "Kill-a- watt" meter--shows, frequency, voltage and current draw.

This situation is found occasionally in marinas. There it is a more serious situation--in that there is more likely to have electrolysis on outboards or thru hull fittings. Sitting on the trailer, this is not a real risk for electrolysis, and most likely no equiptment will be damaged....but there is a risk of a shock should you accidently have a case which has the neutral connected to ground. I would correct the situation immediately.