Reverse Polarity on AC all of a sudden

[NorthernMac]

Hey

My boat has been on the hard for a few days, I’ve had it plugged in to shore power to run the portable air conditioner, I come out to the boat and the A/C systems are not working battery charger as well as the portable air con.

I turn all the breakers off, unplug shore power, check everything, plug it back in, turn everything back on, but the second I turn the master AC breaker on, alls fine, turn any other breakers on and nothing plus I get a rev pol indicator.

On further examination two of the wires going (B & W) going into the AC panel got toasted right at the terminal, with the white one completely separated

Any thoughts?

[a64pilot]

Neutral / ground fault is my guess, after verifying correct polarity at the pedestal. Unlikely but they may have done some work on the Marina’s side.

[NorthernMac]

Originally Posted by a64pilot

Neutral / ground fault is my guess, after verifying correct polarity at the pedestal. Unlikely but they may have done some work on the Marina’s side.

Nothing has been changed on the boat over the last week, as in the boats just been getting painted, nothing has been plugged into or out of the boat, just sitting with the trickle charger and air con on

[SVHarmonie]

Originally Posted by NorthernMac

Hey

My boat has been on the hard for a few days, I’ve had it plugged in to shore power to run the portable air conditioner, I come out to the boat and the A/C systems are not working battery charger as well as the portable air con.

I turn all the breakers off, unplug shore power, check everything, plug it back in, turn everything back on, but the second I turn the master AC breaker on, alls fine, turn any other breakers on and nothing plus I get a rev pol indicator.

On further examination two of the wires going (B & W) going into the AC panel got toasted right at the terminal, with the white one completely separated

Any thoughts?

Based on your description, there is absolutely no way to tell if the damaged wires you see are a CAUSE or and EFFECT of the base problem. Heck, we don’t even know what wires they are!

The most likely cause is a bad connection at the point you see the damage that resulted in a high resistance connection and heat that then “toasted” the wires. But that’s just a SWAG based on almost no information.

If you can’t figure this out, it’s time to call a marine electrician. Seriously, “toasted wires” are just inches away from “fire” and fire is the scariest thing to happen on a boat.

[a64pilot]

Originally Posted by NorthernMac

On further examination two of the wires going (B & W) going into the AC panel got toasted right at the terminal, with the white one completely separated

Any thoughts?

I didn’t notice this until now, but that’s your problem, the white wire is Neutral, and with it being disconnected a there is now a fault in the neutral to ground bond, the fault is of course the neutral is unbounded.

There should be three wires, black is hot, green ground and white is neutral.

This is on the boat side? If so and please don’t be offended, but you should call an electrician, because there may be a fault that caused the wires to overheat and not throw the breaker, likely was just loose, but just hooking them back up without checking everything else out may burn the boat down.

If on the pedestal, then of course don’t touch it, call the marina.

[smac999]

A bad netreal connection will cause a rev pol light. My guess is wires were already bad.

[NorthernMac]

Originally Posted by smac999

A bad netreal connection will cause a rev pol light. My guess is wires were already bad.

Just got a new run of 10g, terminals and a shore power outlet.

[CharlieJ]

Smac999: A bad N connection will not illuminate a reverse polarity light.

The reverse polarity light is connected to the N and G via a >25kohm resistor. If L and N are reversed, the definition of reversed polarity, then the white conductor becomes hot and will light the reverse polarity light.

[smac999]

Originally Posted by CharlieJ

Smac999: A bad N connection will not illuminate a reverse polarity light.

The reverse polarity light is connected to the N and G via a >25kohm resistor. If L and N are reversed, the definition of reversed polarity, then the white conductor becomes hot and will light the reverse polarity light.

voltage drop in the neutral wire will cause a voltage difference between N and G. the light only needs a few volts to start lighting up. it may only be dim and not fully on.

IE you might measure 110v hot to N, 120v hot to ground, 10v N to ground.

the rev pol light will likely be on with 10v across it

it would only light if loads on the boat were on. otherwise the voltage drop would not exist.

[CharlieJ]

smac999:
Don't loose the main point of my post: A bad N connection will not illuminate a reverse polarity light.

Since you brought it up, the voltage drop for a feeder on a pier will cause a small potential on the N. The NEC spec is for <2VAC (I rarely see close >2VAC in Florida in the summer) which may dimly light an incandescent reverse polarity light but probably not an LED. If there is 10VAC across the reverse polarity light, there are probably some serious issues with the dock wiring.

[NorthernMac]

Alls back up to running fine after I replaced that run of wire and I tossed a new shore power connector on too.

I think the root of the issue was someone I hired to install a dripless as I had my shaft out, I found my NEW bilge pump wires were torn too, I think he pushed up some stuff on the back of the exposed power panel and arched it too. Dude is kinda a don’t give a F’ type, older and north of 200lbs, I think in my boat it was like a hog rooting for a truffle and some wiring got the worst of it.

[smac999]

Originally Posted by CharlieJ

smac999:
Don't loose the main point of my post: A bad N connection will not illuminate a reverse polarity light.

Since you brought it up, the voltage drop for a feeder on a pier will cause a small potential on the N. The NEC spec is for <2VAC (I rarely see close >2VAC in Florida in the summer) which may dimly light an incandescent reverse polarity light but probably not an LED. If there is 10VAC across the reverse polarity light, there are probably some serious issues with the dock wiring.

not if the n-g is 0v at the pedestal and 10v at the ac panel. that is a bad n wire causing 10v drop on the wire at load. shut off AC main and load drops and light turns off and n-g voltage goes back to 0

no different then having 12v at a battery and 6v at a device. bad wire / connection

[Uncle Bob]

Originally Posted by NorthernMac

Alls back up to running fine after I replaced that run of wire and I tossed a new shore power connector on too.

I think the root of the issue was someone I hired to install a dripless as I had my shaft out, I found my NEW bilge pump wires were torn too, I think he pushed up some stuff on the back of the exposed power panel and arched it too. Dude is kinda a don’t give a F’ type, older and north of 200lbs, I think in my boat it was like a hog rooting for a truffle and some wiring got the worst of it.

Priceless.

[CharlieJ]

smac999 #12

not if the n-g is 0v at the pedestal and 10v at the ac panel. that is a bad n wire causing 10v drop on the wire at load. shut off AC main and load drops and light turns off and n-g voltage goes back to 0

Look, I am really trying to understand what you are saying but, even after sketching it out, there is no way that a "bad" N conductor is going to cause the RP light to illuminate. And by "bad" I go back to the OP:

On further examination two of the wires going (B & W) going into the AC panel got toasted right at the terminal, with the white one completely separated

and I consider "completely separated" as "bad". In the OP's case, there was no N. That is really bad.

The function of the RP light is to protect a boat from receiving RP shore power when the boat initially plugs in. The RP light is on the line side of the main panelboard shore power breaker.

I just do not understand

not if the n-g is 0v at the pedestal and 10v at the ac panel.

as the most common arrangement is a shore power cable > inlet > inboard cable > panelboard main breaker so we are at opposite ends fo the same conductive paths. How can there be 0VAC N > G at the pedestal and 10VAC N > G at the panel??

I am honestly trying to understand your position but so far I can't see it.

[Boatwright]

Good advice from Charlie.

I note that you were trying to power a portable AC, which can draw heavy amps, especially when starting. High load, bad /loose connections, toasted wires are the known facts. 200# mechanic is a maybe.

I'd be looking at every connection and device between your shore power plug and the AC unit for heat damage and incorrectly installed wiring. I'd also look at the AC unit itself. The cheap compressors can stall when starting and a stalled AC motor can draw very high amps. Repeated hard start, wires get hot, etc......

Before settling on the 200# theory you really need to eliminate all other possible problems. Someone, best a qualified marine electrician like Charlie, who knows how to use a VOM and an amp-clamp needs to do the proper detective work before you start a fire.