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Old 21-05-2018, 17:12   #1
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Burnt Breaker -

What are the causes for this 110v wire to melt the top of this 40A breaker? It is my 110v breaker for everything except the air cons. The wire seems to be screwed in tight still.

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Old 21-05-2018, 17:21   #2
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Re: Burnt Breaker -

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What are the causes for this 110v wire to melt the top of this 40A breaker? It is my 110v breaker for everything except the air cons. The wire seems to be screwed in tight still.

Attachment 170291Attachment 170292
This kind of thing is almost always indicative of a high resistance connection. If the resistance is high enough, even currents that are well below the trip current of a fuse or breaker will generate enough heat to cause serious damage.

On a boat, if the culprit is almost always either a loose connection from vibration or a layer of corrosion from salt or damp.
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Old 21-05-2018, 18:15   #3
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Re: Burnt Breaker -

^^ what bilking said +1
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Old 21-05-2018, 18:32   #4
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Re: Burnt Breaker -

what does the rest of the wire look like? if its not damaged the problem was likely due to being loose or high resistance at the terminal.
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Old 21-05-2018, 18:41   #5
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Re: Burnt Breaker -

Just to add some more info it does not have to be loose for the connection to be poor, leading to high resistance. A poorly executed crimp can be responsible as well, and the wire will seem secure.

Also, this can happen over time. Resistance will build as the wire is progressively heated and cooled, causing the connection to ultimately fail. It's why you should check them on a regular basis: even if they are fine one year, they may not be the next.
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Old 21-05-2018, 19:34   #6
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Re: Burnt Breaker -

Thanks all for the replies!

Here is a little more info.

I didn't see anything loose - but maybe the burnt wire was melted in place.....

The last two inches of the wire going into the breaker had some melting of the cover - the rest looks fine. I'm going to replace it anyway.

Here is a little more info. When I turned on the generator and when the shore power was plugged in - both made the wire hot. So I am guessing both legs coming into the junction is okay.

From the junction (switch for generator / shore power) the wires on it had some melting. So my question - if I replace the burnt breaker and the wire in-between the switch and the breaker - is this a possible fix? Or - could something downstream like the water heater or another device be the culprit? Thanks!! _steve
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Old 21-05-2018, 20:05   #7
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Re: Burnt Breaker -

Also - can someone tell me why this breaker only has one switch on it? There are two wires coming into it - I assume N / L1 (hot). _steve
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Old 21-05-2018, 20:16   #8
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Re: Burnt Breaker -

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Also - can someone tell me why this breaker only has one switch on it? There are two wires coming into it - I assume N / L1 (hot). _steve
Common trip for neutral and hot. One lever operates both.
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Old 21-05-2018, 21:46   #9
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Re: Burnt Breaker -

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So my question - if I replace the burnt breaker and the wire in-between the switch and the breaker - is this a possible fix? Or - could something downstream like the water heater or another device be the culprit? Thanks!! _steve
your issue is where the burn is. something was loose or corroded at that point.
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Old 22-05-2018, 10:02   #10
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Re: Burnt Breaker -

You would be wise to re-tighten all the breaker connections that you can access. This might avoid some future problems. Also, re tighten the connections on the new breaker after a day or two.
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Old 22-05-2018, 10:41   #11
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Re: Burnt Breaker -

Just reading your diagram quick it indicates 6mm2 wire which is close to 10 AWG which would be light at 40 amps. Might want to confirm what size wire is installed there. Also did you say the other end of the wire at the transfer switch was also getting hot?
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Old 22-05-2018, 11:03   #12
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Re: Burnt Breaker -

Have you been using an electric heater a lot? It's common when doing that or other large loads.
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