Reverse polarity light

[STB]

So, I was on a friend's sailboat, there to fix an outlet that stopped working. He'd tried to fix it and found a "black wire disconnected in the main panel, out an end on it, and connected it somewhere on the black bus". He didn't remember where.

I found a couple of other AC wires pulling out of their connectors and sparking and corrected them. And then found that the outlet wire had been connected to the refrigerator breaker and moved it. That fixed the problem. No one knows how it moved itself, but he doesn't think it is the one he attached, because the connector is old.

As I was checking over the panel, I found the 12v wire from the breaker to the bus to be very hot. None of the screws holding the breakers to the bus side were tightened at all. They were mostly unscrewedans arcing could be seen when wiggled. I corrected that. He has no idea how long it has been that way
He thinks, maybe, since the PO rewired years ago.

I also noticed...and here is my question....the reverse polarity LED (tiny) light is on if, and only if, the main 120v breaker is off and /any/ one or more 120v branch breaker is on. It is off when the main is on or if all branches are off. I got as far as checking the pedestal, shore power cable, and inlet, as well as swapping pedestals and cables. I also put his meter from N-G and got ~0-Ohm when connected to the pedestal and, when the problem was occurring, ~62v N-G...but I believe that was likely a ghost reading from inductance or capacitance and didn't have my gear to load it and see. Also, the reverse polarity light was brighter the higher up in the panel the breaker I turned on. He reported that he never saw it before and thinks it must be related to whatever wire he connected. But, I'm not sure he ever looked at the breaker panel in that state.

I won't be able to go look again for a few days, but when I do, I'll be able to bring my own toolbar, etc, and spend time on it. By the time I noticed it last time it was already past time to go.

So...I'm not dealing with reverse polarity. Anyone seen this before? Any guesses? I'm almost wondering if it is the circuit-on LEDs, themselves. This seems like it'll be fun to trouble shoot.

And, yes, I know the whole thing needs gone through. I just mentioned the other issues to give the sense that anything and everything is on the table.

 

[CharlieJ]

At first blush it appears that there is a N > G bond aboard as the resistance between N & G should be >25kohms.

 

[STB]

At first blush it appears that there is a N > G bond aboard as the resistance between N & G should be >25kohms.

Thanks!

I understand that since there is no inverter or genset, that should never be the case (versus being the case only when either is actively in use).

How would that turn on the reverse polarity light?

Thanks again!
-Greg

 

[CharlieJ]

@gkesden
The easiest way to understand reverse polarity indicators (RPI) is to draw a simple sketch with Line, Neutral and Safety Ground. The RPI is connected between Neutral and Safety Ground and current is limited by a 25kohm resistor. Since there is usually a small difference of potential between N and G because of voltage drop in the N from the shore power feed at, the resistor will limit the current so that the RPI will not illuminate.

When a reverse polarity condition exists, L and N are reversed and the RPI is subjected to near line voltage between N and G and the RPI illuminates.

 

[STB]

Hey Charlie,

Thanks again!

I am with you so far. But, what I am not seeing is how having N and G bonded within the boat can cause a RPI to illuminate, never mind only/exactly when the main breaker is switched off and any one or more load breaker(s) is switched on. What is the potential current path?

In this situation, I know that from the pedestal through the entry to the main panel, the wiring is correct for N, L, and G. When I noticed the issue, I started back at the pedestal, checked it with a meter, then checked the other side of the cable with a meter, then checked the input to the panel with a meter. Then, I took the power cord, supplied form a different pedestal, from a neighbor boat and plugged it in, swapping out the pedestal and the cord, and checked again. Unfortunately, I ran out of time before I moved forward into checking into the main panel and branch circuits. That'll likely be this weekend.

So, I really don't think the situation is an actual reverse polarity situation. But, I could be wrong and maybe I should recheck.

Can you help me to understand? Thanks!

 

[SteveK]

Hi Charlie,
with no onboard inverter, no other onboard power, can that light be lit from 12V + leak?

 

[STB]

Hi Charlie,
with no onboard inverter, no other onboard power, can that light be lit from 12V + leak?

That's more along the lines of what I was thinking/expecting. I did try with the 12V breaker and both battery switches off. Having said that, what might be hard wired, etc, I don't know.

I was also sort of wondering if those LEDs might be such a small draw as to be able to be lit by inductance, etc.

 

[DrissZougari]

1) The Ground and Neutral should never be connected on the boat (please perform this test after you disconnect the shore power from the pedestal).
2) Check your shore Power cable for open Ground or Neutral as it will cause reverse polarity light to turn ON.

 

[SteveK]

1) The Ground and Neutral should never be connected on the boat (please perform this test after you disconnect the shore power from the pedestal).
2) Check your shore Power cable for open Ground or Neutral as it will cause reverse polarity light to turn ON.

Did you mean closed? open to me means G&N are not connected, closed to me means connected. But even if they are connected with no AC power on boat it is coming from the cord or pedestal.

 

[SteveK]

That's more along the lines of what I was thinking/expecting. I did try with the 12V breaker and both battery switches off. Having said that, what might be hard wired, etc, I don't know.

I was also sort of wondering if those LEDs might be such a small draw as to be able to be lit by inductance, etc.

found a "black wire disconnected in the main panel, out an end on it, and connected it somewhere on the black bus"

I am thinking that black is a 12V + (maybe), hope not

 

[High Wire]

Since 120VAC Black is the HOT (L1) and 12VDC Negative is also Black, you better go back to each of those black wires and trace them. Crossing the two systems can be spectacular in a bad way. That's why ABYC changed 12VDC Negative to Yellow.

 

[DrissZougari]

I second High Wire !

Soo-Valley, in order to verify that your ground and Neutral are not connected on your boat (this is bad), you should disconnect (Yes disconnect) the shore power cord from the Pedestal. Pedestal breakers do not disconnect the N & G lines from the boat and yes they are connected on the dock.

 

[STB]

1) The Ground and Neutral should never be connected on the boat (please perform this test after you disconnect the shore power from the pedestal).
2) Check your shore Power cable for open Ground or Neutral as it will cause reverse polarity light to turn ON.

Thanks for your feedback!

And,, you are spot on in this situation. But, just to note for posterity, in case a later reader misses the context, in different situations where an onboard inverter or generator are supplying the AC, the inverter or generator should bond N-G while acting as the supply, e.g. via an output relay.

 

[STB]

found a "black wire disconnected in the main panel, out an end on it, and connected it somewhere on the black bus"

I am thinking that black is a 12V + (maybe), hope not

Yeah. I almost fell over when he told me that he'd done that and nearly cried when he couldn't remember which wire. But,, we all do silly things sometimes, I guess..

When I go back I'm going to use one of those light-up AC sensors to check his 12V circuits at the panel.

But, what has me surprised here is that I did shut off all batter switches and the 12v main at the panel. Soz if it is a 12v issue, it would seemingly be something directly connected or chaffing or getting an induced voltage or whatever somewhere else, nit at the panel.

I also think, with 20-20 hindsight, the fact that the LEDs brightness varies with how high up or down the breaker I turn on is in the panel will turn out to be a missed clue :-(

I have a feeling this is going to be an all day job.

 

[STB]

I find it interesting also that he is in the process of selling the boat and it was professionally surveyed earlier this very same day. The electrical passed with no reported issues other than a GFCI that wouldn't reset.

It was this issue that cause the owner to dig into the electrical, then to call me. I "fixed" the GFCI issue (it was, by magic, connected to the wrong breaker).

It was in the process of looking things over after that that I found the other issues, and then this one. But, ran out of time before I could really dig in...working my way from the pedestal to the panel input looking for a problem, but not getting past that.

The loose DC bus was a dramatic fire hazard...I noticed when the wire was hot to the touch touch I saw sparking as I touched it to investigate. I can't imagine that being missed.

It'll be interesting to learn what conversation he has with the buyer once this is fixed. I guess he'll just tell them that he resolved the GFCI issue, that it was just on the wrong circuit, and did some other maintenance along the way. Dunno'.

 

[Lou_tribal]

This is the time to say: get an electrician who knows what he is doing so you won't risk your boat, or your life, based on hypothesis from people on the web who did not see your boat setup.

Note: No critic on people trying to help, just that without clear understanding of the boat setup the result may be bad.

L

 

[STB]

This is the time to say: get an electrician who knows what he is doing so you won't risk your boat, or your life, based on hypothesis from people on the web who did not see your boat setup.

Note: No critic on people trying to help, just that without clear understanding of the boat setup the result may be bad.

L

Well, this isn't my boat. I'm the "guy on the dock who people say fixes stuff for free" on this project! I hope I'm worth no less than I'm getting paid. No guarantees.

I feel sure I'll be able to find and fix this specific problem. The boat clearly needs a full and competent electrical inspection. But, I suspect he'll leave that for the buyer who, sadly, thinks he had one and probably paid a lot of money to that surveyor.

I was just sort of hoping that some folks here may have seen this problem or similar before and could offer me some good candidates. Otherwise, I'll go at it from 1st principles.

I'll check the 12VDC for 120VAC with a simple proximity tester (don't know if it is a current transformer or hall effect or whatnot), then the 120VAC for 12VDC with a meter. Then I'll try to put a variable resistive load from neutral to ground and see what the voltage curve looks Iike to get a sense if I've got a "real" current source or side effect or a transient. Then, if indicated, isolate the batteries by pulling ground.

If I had to make a wild guess right now and get it right or die, I'd probably be dead, but I'd guess it is somehow relates to his battery charger. I doubt it is being isolated by the battery switches on the output side. The chassis ground could be to AC only vs DC or could bridge dunno' what if miswired.

My next guess would be a problem with a surge suppressor somewhere with some caps or MOVs on neutral that could be failing.

I just really dunno. I'll find it. But I think it is going to turn out to be a lot of work for something silly in the end. Hoping for a shorter path!

 

[SteveK]

I am not saying do as I would do.
If it was me i would turn off all breakers with shore power connected and use a jumper from Line hot to load neutral. The reverse polarity led should light up bright. This would confirm the led is wired correctly.

 

[STB]

Hey Soo-Valley,

That sounds like a good idea....but I'll probably just check the diode orientation with a meter rather than live.

I'd be a little surprised if it is backward, only because it doesn't light when the system is attached correctly to correct shore power and turned on at the main.

 

[CharlieJ]

Regarding surveys: Surveyors will not generally open a panelboard so the electrical inspection is relegated to a GFCI test or, if they are really competent, a circuit test using an IDEAL SureTest.

And to underline gkesden Post #13: A N>G bond is required at any source of power. Onboard those sources are: inverters or inverter/chargers when inverting, generators and the secondary of isolation transformers.

 

[ancora]

Whenever we turn off the AC breaker on the boat, the reverse polarity light comes on. It's been doing that for 21 years and we're still alive.

 

[Var Korall]

How old is the boat? Are you sure the indicator light is an LED? If the boat is older it may not be an LED, which might make a difference to your testing.

 

[STB]

How old is the boat? Are you sure the indicator light is an LED? If the boat is older it may not be an LED, which might make a difference to your testing.

I haven't been able to get back onto the boat, yet. The sale apparently fell through and the owner hauled it for routine bottom work.maybe this weekend.

The boat is, approximately, a 1981 C&C 40' sailboat. It was apparently rewired by a prior owner.

I'll double check, but they looked like LEDs to me, st least at a casual glance.