Polarity Alarm Help Please

[Steve L22188]

Went to the boat today after about 3 weeks of non use. The guy two boats up says, "there's been strange buzzing in your boat." I ask: what kind of buzzing...like bees. "No. " he says, "Like electrical buzzing."

He shows me where the buzzing was coming from -- right behind the electrical panel. I check the panel - nothing wrong that I can see. Only thing turned on was the shore power and the battery charger. I hit the polarity check switch and he says, "That's it! That's the noise."

A little further detective work and he then admitted that he had also unplugged the shore power cord for a few seconds and then the noise stopped.

Then, when I was putting the boat away today, I had a brief (less than a second) buzz from the polarity alarm when I plugged in the shore power cord. Happened just when the shore power cord made contact with the receptacle.

I've always thought the polarity issue was based on a electricity supply problem - am I right?

Or is this likely a bad shore power cord (it's about 20 years old but has given me no problems)? Or is this bad juice from the supply at the box?

Checked both ends of the shore power cord and no signs of any sparking, heat or discoloration.

Can an electrical guru (or a dozen of you) give me a sense of what might be going on?

Thanks so much.

 

[Bill Roosa]

You might want to check and see if the marina has done any electrical work on your dock since this began. However, since no one else is having the same issue I'm thinking it is either your slip outlet (marina maintenance) or you have one of the following:
bad Shore power cable (ckeck with a multimeter, should read 110-120 volts between both hot-neutral and hot-ground, and 0 volts between neurtal-ground)
a leak from hot to neutral somewhere (probably the battery charger wiring but could be in the buss behind the panel)
polirity indicator has gone bad (if you check the polarity at the panel busses and they are ok then it almost has to be the polirity indicator)

 

[zeehag]

is your plug twisted into the socket tight?

 

[Don12364]

I like the sound of your reverse polarity detector (pun intended).

If it also sounded when the ground wire was disconnected it would warn of this situation which is possibly more dangerous than having hot and neutral interchanged.
Such a circuit is simple and the manufacturing cost only pennies more than the standard type of circuit.
At a guess I would suspect that your ground wire has become intermittent at either of the shore power plugs.
Suggest you plug in, wiggle the wire at each plug and listen for the tell tale buzzer.

 

[Bill Roosa]

For the record, the reverse polarity warning system detects ac current in the neutral wire. It does this by powering a buzzer with the neutral and grounding it with the ground wire. So if your ground is bad you don't get a sounding buzzer. If you don't have ac current supplied to the neutral you dont get a buzzer. This is all pretty easy to test with a volt meter.
WARNING 110 volt AC can kill. While you are pretty safe probing a shore power outlet or cord going behind a hot panel can get you into trouble. If you are not sure of what you are doing get some help. roosaw@verizon.net Any boat owner worth his salt should have a familuarity with 110 volt ac.

 

[Maine Sail]

For the record, the reverse polarity warning system detects ac current in the neutral wire. It does this by powering a buzzer with the neutral and grounding it with the ground wire. So if your ground is bad you don't get a sounding buzzer. If you don't have ac current supplied to the neutral you dont get a buzzer. This is all pretty easy to test with a volt meter.
WARNING 110 volt AC can kill. While you are pretty safe probing a shore power outlet or cord going behind a hot panel can get you into trouble. If you are not sure of what you are doing get some help. roosaw@verizon.net Any boat owner worth his salt should have a familuarity with 110 volt ac.

The standards have changed since then in place to make sure the light goes on when it should. My guess is that this system still uses a 25k resistor for the RPI light?

The ABYC requirement for reverse polarity indicating lights is that they use minimum 25k Ohm Resistor. This is so they "indicate" at below the 5mA that a standard US spec GFCI will trip at. In the old days the indicator lights were neon based and for the last 20 or so years they have been LED but all should still have a 25k Ohm resistor in the circuit. Perhaps Hunter used an alarm and light together? This light sits between the AC white/neutral and AC green/earth ground and responds to a reversal of the ungrounded (black) and the grounded (white) conductors .

Keep in mind that when Muffy and Biff fire up the brand new Sea Ray, untie the dock lines, and steam away from the dock forgetting about the power cord, it is usually Darrell the dock boy and his other buddy Darrell who re-wire the dock post. Don't trust them and start with a test of the dock post for reverse polarity. If you don't have a tester or DVM ask the marina to test it for you. It would be good to be there to watch it..

In lighted circuit RPI designs it is possible for the reverse polarity indicator circuit to faintly illuminate even though the circuit is properly wired. This often occurs from voltage drop but some inverters and even some battery chargers have been known to cause this as well due to leakage. To test this you can simply disconnect your inverter or charger and see if the RPI is still faintly lit, if that is what you're getting.

Thanks to a guy name Ohm, and his law, voltage is always consumed trying to push amperage through a wire. If the voltage differs between the beginning and end of the run or any two points in-between this is called voltage drop. Voltage drop can be caused by undersized wiring, improper or poor connections / terminations or corrosion. It is possible a battery charger cycling on and off could have caused the alarm to sound. Bad or loose friction fits, in shore power receptacles, can also cause some voltage drop or resistance. This difference in voltage is what can dimly illuminate a RP indicator light.

If you flip on a high amp draw load there can often be enough voltage drop along the neutral path to overcome the resistance in the 25,000 Ohm resistor thus lighting it faintly. Voltage drop is not as dangerous as sucking on live wires, but should be attended to if discovered.. Check all connections, use a tester, and make sure your AC input wiring from the dock to the panel are sufficiently sized for your loads. In some cases just trying a different dock pole and shore power cord can eliminate issues on-board and isolate them to the cord or dock post..

It sounds like you may have a bad receptacle or cord but check everything. If you want to convert your system to the current safety standards an RPI light can be purchased from Blue Sea..


ABYC E11 - SHORE POWER POLARITY DEVICES

E-8.10.1 Reverse polarity indicating devices providing a continuous visible or audible signal shall be installed in 120 V AC shore power systems and must respond to the reversal of the ungrounded (black) and the grounded (white) conductors (See E-8.23.1, Diagram 3,)

E-8.10.1.1 the polarity of the system must be maintained for the proper operation of the electrical devices in the system,

E-8.10.1.2 a branch circuit is provided with overcurrent protection in only the ungrounded (black) current-carrying conductors per ABYC E-8.11.6.1

E-8.10.2 Reverse polarity indicating devices are not required in systems employing polarization or isolation transformers that establish the polarity on the boat.

E-8.10.3 The total impedance of polarity indicating and protection devices connected between normal current carrying conductors (grounded [white] conductor and ungrounded [black] conductor) and the grounding conductor shall not be less than 25,000 ohms at 120 volts, 60 hertz at all times.

 

[Steve L22188]

Many thanks to all

Thanks to all of you for your help. I appreciate it very much. This is such an incredible group of people.

I'll return to the boat on Friday with a friend who understands electricity better than I.

I suspect this will turn out to be one of two things:

1.) a bad shorepower cord (it was new in 1990!) Probably prudent to think about a new one after 20 years of being in and out of the harsh Kansas weather. or....

2.) Larry, Darrell and his other brother Darrell. The owner who put in the marina was an incredible jack of all trades and master of none. Half of what he did, he over built. The other half, he did half-assed. The problem is that his judgement of what half to use as his quality standards seems a bit suspect at times.

I'll report back on what we find. Again, thanks again.

Steve

 

[Steve L22188]

Update....

Back to the boat yesterday. Grabbed the meter to check the voltage readings as many of you suggested - then discovered the battery was dead on the meter (Murphy was alive and well).

Laying in the v-berth this morning (is there an easy way to get in and out of those?) I had an elegantly simple test hit my brain: I plugged my shorepower cord into my neighbors receptacle. Jackpot! The polarity light indicator immediately went from flickering to full bright.

The rascal seems to be the receptacle and not my shorepower cord or the innards behind the electrical panel.

Called the marina and either Darrell or his other brother Darrell said, "Oh yeah, we've been having some trouble with those boxes over there."

They've promised to fix it either this afternoon or on Monday. We'll see.
Thanks again to all of you for your assistance.

Steve