Reverse Polarity on AC all of a sudden

[NorthernMac]

Originally Posted by 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.

Everything else on the back of the panel was secure with no signs on heat damage, I had it running for 7hrs while I was working on the boat, checked it before I left and nothing was really hot, tracing the run to the outlet the AC is plugged into, looked good, was secure and didn’t feel hot.

[OloteleMtn]

I chuckle at the idea some of you think 200 pounds is large....and that competence is tied to size.

[NorthernMac]

Originally Posted by OloteleMtn

I chuckle at the idea some of you think 200 pounds is large....and that competence is tied to size.

Competence is tied to competence, and size makes it harder to get into some spots.

This guy is like 250lbs and 5’8” that’s fat, as someone who worked EMS, no bueno. There are some personality attributes that go along with being that size, not popular to say but true

[Boatwright]

Originally Posted by NorthernMac

Everything else on the back of the panel was secure with no signs on heat damage, I had it running for 7hrs while I was working on the boat, checked it before I left and nothing was really hot, tracing the run to the outlet the AC is plugged into, looked good, was secure and didn’t feel hot.

I hope your focus on the toasted wires doesn't prevent you from finding the cause. The overheated connection should be looked at as the [U]result[U]not the cause of the problem. You fixed the toasted wires and everything works again, but the question still remains: Why did the wires overheat?

One thing we do know is you ran the AC for 7 hrs. Again, 110 V AC units are well known for running right at the max allowable amperage of the circuit in question. I won't even go into the possible effects of voltage drop, the thermal expansion of heavily loaded wires loosening connections, etc.. The other thing we don't know is what happens if, thinking the problem has been fixed, the AC unit cycles all day and again [U]causes[U] a problem.

Suggestion: Buy a heavy 12 ga. extension cord and power the AC separately from your boats wiring. In the future avoid plugging in high amp continuous run appliances -- AC, space heaters, etc. -- into your boat's branch circuits.

Good article from Boat US insurance: https://www.boatus.com/magazine/2018...s-on-boats.asp

[keepondancin]

How is a boat electrical system grounded when it is on the hard, keel sitting on wood, and how does that have a effect on the newest style of GFI outlets?

[NorthernMac]

Originally Posted by Boatwright

I hope your focus on the toasted wires doesn't prevent you from finding the cause. The overheated connection should be looked at as the [U]result[U]not the cause of the problem. You fixed the toasted wires and everything works again, but the question still remains: Why did the wires overheat?

One thing we do know is you ran the AC for 7 hrs. Again, 110 V AC units are well known for running right at the max allowable amperage of the circuit in question. I won't even go into the possible effects of voltage drop, the thermal expansion of heavily loaded wires loosening connections, etc.. The other thing we don't know is what happens if, thinking the problem has been fixed, the AC unit cycles all day and again [U]causes[U] a problem.

Suggestion: Buy a heavy 12 ga. extension cord and power the AC separately from your boats wiring. In the future avoid plugging in high amp continuous run appliances -- AC, space heaters, etc. -- into your boat's branch circuits.

Good article from Boat US insurance: https://www.boatus.com/magazine/2018...s-on-boats.asp

That AC has been running on the boat for the last 5mo

I’ll also be installing a onboard heatpump soon so if the wiring can’t take it, I need to fix that problem. That said, never been a issue before, I’ve even run the AC with sanders too.

Originally Posted by keepondancin

How is a boat electrical system grounded when it is on the hard, keel sitting on wood, and how does that have a effect on the newest style of GFI outlets?

Yup, on wood blocks, new outlets and 8yr old wiring looking to be in good shape, do need to add a GFI.

[a64pilot]

Originally Posted by keepondancin

How is a boat electrical system grounded when it is on the hard, keel sitting on wood, and how does that have a effect on the newest style of GFI outlets?

A boat doesn’t use water as a ground if that’s what your thinking, the green wire in the AC wire is the ground.
Now it should also be understood that the ground in a AC system, when one exists, is only a safety wire, it doesn’t carry, or shouldn’t carry any current ever, it’s there sort of like a seat belt.

In a DC electrical system there are only two wires, the power and the ground, power comes from one wire and the circuit is completed by the other.

In an AC system the black wire is the “hot” wire and the circuit is completed by the white wire, the “neutral” is the return wire, the green wire is the ground wire which is a safety backup, in fact the green and white wore should be connected together at the source of the power, making then both in effect the same.