Smoke In Cabin - Fire Averted!!! Breaker Failure?

[flightlead404]

Whilst sitting and eating lunch a few minutes ago my girlfriend commented on a funny smell. It was rapidly increasing in intensity and I quickly tracked it to the AC panel. When I popped the panel open there was visible smoke, but not enough to determine the source.

I quickly turned off every breaker and it ceased. Touching the breakers I found the AC Line #1 30A breaker to be rather warm.

Turning on the suspect breaker the voltmeter shows around 55-60V. I get the full 120v on Line #1. Checked and swapped the two 30A lines coming into the boat the issue stays with Line #1.

First concern, if I hadn't caught this would I have returned to find a pile of burnt plastic instead of a boat?

Has anyone experienced this before?

Moving forward I need to get a replacement breaker. Is there a source for matching breakers?

As an interim, I have a paralleling switch. Can I run Line #1 side items off Line #2 with that switch? I've only every done it the other direction (or with generator).

 

[flightlead404]

Culprit found!

Carefully examined each wire and connection. Found the 8AWG from Line #1 breaker to buss bar to be charred (see picture). Checked the terminal screw at that end. It was loose and had some appearance of corrosion.

Checked every screw on every breaker, connection, terminal block etc on both AC and DC sides. Found several that were loose, tightened them up. In the process found the terminal screw for line from buss bar to main aircon unit breaker to also be loose - like maybe finger tight. That particular breaker was molested only 8 months ago when the PO had new aircon installed! That 8AWG line was HOT but showed no sign of heat damage to the insulation.

Swapped out the charred line, all now seems to be fine. Monitoring closely for a while.

Morals of the story:

1. Smoke means you ACT IMMEDIATELY, don't mess around, and don't hesitate to pull panels to find the source, like right now!
2. If the smoke stops, don't shrug and waive it off. Keep plugging until you've found the issue.
3. Always follow up behind hired help no matter how "expert" they may be
4. Periodically check these terminal screws - its now on my checklist of preventative maintenance

 

[JamesG161]

I need to get a replacement breaker. Is there a source for matching breakers?

Yes!!
Look here...
Hunter 38 breakers, double pole, single throw
Jim...

 

[flightlead404]

Yes!!
Look here...
Hunter 38 breakers, double pole, single throw
Jim...

Cheers mate. Unsure at this point if the breaker is actually an issue. However I would have expected it to trip since the wire was charred. Once I cleaned and tightened the screws the voltmeter reads correctly and the leads aren't heating up except the aircon one is a little warm. I may uprate that one to 6AWG.

I may just replace the two main a/c breakers and the breaker for paralleling out of caution since they carry the heaviest loads and have 17 years in a marine environment on them.

 

[JamesG161]

However I would have expected it to trip since the wire was charred

well down stream, a lose connection and a slow heat up, may not trip until too late, like you pointed out.
____

I had to replace one from a shoreline lightning strike.
It fit perfectly.

I would get one just as a spare , not too pricey.

That buss and is key to 120 VAC power.
Jim...

 

[Ralph Johnstone]

Unsure at this point if the breaker is actually an issue. However I would have expected it to trip since the wire was charred.

But you've already solved the problem.

The terminal on the #8 AWG to the buss bar was corroded and had a voltage drop of (120V - 60V) = approximately 60V. This is what generated the heat to burn the wire, not excessive amperage. Voltage drop X amps = watts at the corroded terminal.

Your breaker never saw an excessive amperage therefore the breaker never tripped.

 

[flightlead404]

But you've already solved the problem.

The terminal on the #8 AWG to the buss bar was corroded and had a voltage drop of (120V - 60V) = approximately 60V. This is what generated the heat to burn the wire, not excessive amperage. Voltage drop X amps = watts at the corroded terminal.

Your breaker never saw an excessive amperage therefore the breaker never tripped.

True, it was high resistance downstream, not low resistance aka a short.
I’m going to carry a spare anyway.

 

[njlarry]

Your girlfriends pretty little nose saved your boat.
Thanks for posting.