Burned line wire at circuit breaker

[honkydog]

Looking for some help on with AC electrical issue.

Over the weekend we returned from a cruise and plugged into shore power. Shortly thereafter, smelled electrical burning. Shut things down and took ac panel cover off and found line wires burned at connection to the circuit breaker that is connected to AC unit 2. The wire that burned is the one providing power from shore #2 main breaker (shore #2 has 2 ac units and ac water pump), as best I can tell. The other two circuit breakers then receive line power in daisy chain fashion from this breaker, and are connected to ac unit 1 and the ac water pump. None of the breakers tripped, but eventually the daisy chain connection to the second circuit breaker burned through so ac unit 1 and the ac pump no longer received power. Ac unit 2 continued to operate. I ohmed out the compressor on ac unit 1 and it checked out good.

A couple of questions because master boat electrician I am not. Because this happened on the line side, it seems to me this was caused by a loose/corroded connection of that wire to the line side of the circuit breaker. I plan to rewire and then check to see if all is well. Also, plan to replace that breaker when I can locate one (boat is a 95 and in a quick search I didnt locate a readily available replacement). Are there any other possible causes or concerns I should consider?

[bud37]

Have a real good look at your shore power plug and the connection there as well......along with the wiring going back to the plug. Maybe someone else will jump in but until you reconnect all the new wire it will be difficult to see where the damage went to, interesting how the breaker did not trip, there is a lesson there me thinks..

The breakers can usually be found on Blue Sea...good luck with it.

[Viper]

People put too much faith in breakers IMO. They don't always trip under those circumstances. Those wires can catch fire and still not trip the breaker, happens all the time, especially on dock pedestals. Ya it's likely due to either a loose connection that could be anywhere in the circuit meaning the shore power cords, inlets, connections at the breakers, etc. Look for discoloration at you cords' connector pins. By their very design, they make for a poor connection to begin with even when new. The SmarPlug is a way better design but there are limitations on the marina side as the old plugs are typically what marinas have, but that's another thread, don't get me started on that! I'd also check how much of a load there is when everything on that leg is running and ensure it's within that circuit's safe operating capacity. One of the loads may be drawing more than usual for some reason; low voltage?

[Carpediem]

I found burned wires in my AC panel on my SeaRay 44DB with only 120 hours on the boat but it was ten years old. The terminals were loose causing the arching. I inspected and tightened the rest of them many of which were loose. It is not something one would regularly check but I do when ever I have a panel like that open.

[Phrancus]

note that you can't tighten them very often without deforming and thus creating a 'tired' thread which comes loose sooner than before. No matter how hard you turn it, if its beyond the torque it was designed for, the screw fails and you've created a weaker connection while trying to do good.

It is good to check for loose wiring, joints, plugs, sockets by lightly pushing and pulling the wiring. And it's ok to put a screwdriver on and feel but don't go tighten them right away with force thinking that any movement is better and is proof of a too loose connection. The wire was deformed the first time, sort of springs back and keeps the connection tight. Overtightening flattens is too much, taking out the elasticity and thus strength.

Bit like a screw into a plastic hole: just enough torque and all is well. A bit too much and the plastic deforms. More too much and it cracks.

[honkydog]

Thanks all for the thoughts. I rewired connections with new boat cable and then energized each load one by one. Pulling 20 amps when all loads switched on, and connections are remaining cool. Fingers are crossed that it was just a loose connection.

[Phrancus]

20A @ 110 is about 10A @ 220 (standard in my part of the world) and that sounds reasonable for an AC starting up.

we have 6A max on the dock here and guests generally have to start up their generators (no pun intended) so 10A sounds OK.

nevertheless: check regularly, also without cause. just to remain sure that all is well behind the shiny bits of your boat.