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Old 06-27-2020, 06:40 AM   #1
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Very Hot 60-amp Alternating Current Circuit Breaker

This is the breaker (Square D) on the feed from my 7.7kw Westerbeke. Yesterday, this breaker tripped twice with modest loads and was very hot to the touch. I opened the box this morning and could see nothing obviously wrong except the green line in from the generator is butt-spliced twice. The engine room was very hot but this is nothing new.

My thinking, my knowledge is very limited in this regard, is that the breaker has developed a high internal resistance over time. Am I on the right track or should I be looking elsewhere? We have used this generator extensively over the past two years but I have to admit that I never once felt the breaker box for heat so that this condition may have existed for a long time and is just now becoming acute.
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Old 06-27-2020, 07:04 AM   #2
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Circuit breakers should not be hot to the touch. Replace it.

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Old 06-27-2020, 07:07 AM   #3
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It is usually a symptom of a bad connection due to corrosion or looseness. Not always easy to see with a glance. Check all that thoroughly. Typically those sort of breakers are not very expensive, if that's where your investigation leads you.
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Old 06-27-2020, 07:10 AM   #4
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Yes it is possible that the breaker has seen better days.
I used to work with manufacturing residential circuit breakers and they do wear out especially if they are cycled often with high load. The contact points can arc and get pitted then they heat up and trip.
I had a 30 amp breaker fail in my boat.
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Old 06-27-2020, 07:28 AM   #5
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Is that generator 120 VAC or 240 VAC? Normally I would expect a boat of your size to be wired with two 30 amp or one 50 amp 240 volt shore power connection. So, typically the breaker on that generator would be a double pole 35 amp breaker. Seems odd that you have a 60 amp breaker.

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Old 06-27-2020, 08:31 AM   #6
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Is the breaker in question the one mounted on the genset itself? If so the "book" should have an electrical diagram noting the OEM breaker specs.
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Old 06-27-2020, 09:07 AM   #7
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Most of these breakers have two trips: One is thermal where a heating element in line with the load trips it if they get too hot. The other is magnetic that trips it rapidly on a very high overload. So some heat is normal. But if the thing is noticeably hotter than surroundings on modest load, contacts are in bad shape or connections have high resistance.

If connections are solid (snug them) and it is still hot, replace it.
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Old 06-27-2020, 11:08 AM   #8
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Breakers go bad in normal use and from abnormal conditions. Check the loads with a clamp meter. Check voltages on both legs to neutral and ground, and to each other, loaded and no load.

Bad breakers can make a freak show of oddball electrical problems.


Be sure to get the right replacement. Don't just match the existing breaker.

Mostly, protect yourself while working with electrical issues. Ever see one of those hot dog cookers where the hot dog is the conductor? Don't be a hot dog.
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Old 06-27-2020, 11:23 AM   #9
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I would certainly swap it out. If it is a Square D breaker it will be cheap and easy to swap so why not give it a try. If it still trips then look more closely at the system.
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Old 06-27-2020, 11:57 AM   #10
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Circuit breakers do indeed fail.
However, do some checks first. If the fault is not the C.B. itself then a new one will repeat the problem.

Check the actual connections for ANY sign of oxidation which is darkening the lug and the wire .
Check the wire insulation for any sign of discolouring indicating heat buildup.
Check also for looseness as looseness will lead to oxidation .
Any looseness and resulting oxidation will create resistance which will create heat buildup which will discolour the wire itself, its insulation AND likely the C.B. terminal
THat heat buildup will also cause nuisance tripping.

I have had decent results with reterminating the wire back to bright wire or heavy wire brushing, SS wire brush, both the wire and the C.B. side terminals if discoloured and then applying some NoAlox or similar.

But if all are not tight and clean it will repeat.

Before I forget check the actual current flowing through the C.B. Maybe the draw is borderline and with a wee bit of oxidation it goes over the edge.

If the terminals are tight and clean now then the C.B. itself is the likely culprit.
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Old 06-27-2020, 01:08 PM   #11
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Thanks guys for your ideas. I will replace the breaker and report back. This is a 50-amp boat.
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Old 06-27-2020, 01:10 PM   #12
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Another thought. Why do I even have a circuit breaker? On board is another generator, a Perkins-powered Kohler 12.5kw. The output is wired directly to the panel, no circuit breaker.
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Old 06-27-2020, 02:33 PM   #13
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Kohler genset is non-compliant as the wire run from the generator to the panel is unprotected by an overcurrent protection device (OCPD).
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Old 06-27-2020, 03:35 PM   #14
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Ah, I always wondered about that. I will look into adding protection on that circuit. Question: how would over current occur coming from a generator that puts out a constant?
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Kohler genset is non-compliant as the wire run from the generator to the panel is unprotected by an overcurrent protection device (OCPD).
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Old 06-27-2020, 03:40 PM   #15
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Compromised insultation on the output cable.
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Old 06-27-2020, 06:28 PM   #16
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Which Kohler 12.5kw genset do you have? What is the model, drawing, and/or build number? Some have over-current protection built into the unit rather than leaving it for one to wire up in a nearby electrical box.
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Old 06-28-2020, 12:21 AM   #17
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The RATING you see is not a constant. That rating is the maximum current that it can produce safely without overheating and causing damage to itself.

Under a short circuit condition the amperage could climb greatly although the output voltage would falter.

A C.B. or fuse is needed to protect against shorts. Are you sure there is not one installed as part of the gen set itself?
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Old 06-28-2020, 01:33 PM   #18
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Report - The breaker had to be pried out with a screwdriver. The spring contacts were highly encrusted. Much resistance right there. The plastic housing near the contacts was melted from the heat. The box is being replaced as well. Now, take a look at the picture. Notice the corroded, breaking and broken strands in one of the wires (after I removed the electrical tape) that were connected in an unacceptable manner. Frightening, isn't it? Needless to say, the wiring and connections will be updated properly. There are three black wires that were connected together. Two come from the generator head. The third is the run to my electrical panel along with a white wire and a green wire, all 6 AWG.
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Old 06-28-2020, 02:02 PM   #19
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That is some great electrical work there... I would replace the wiring if it is damaged and instead of using a nut and bolt put them on a terminal block. Maybe do an electrical survey of the boat. If they did this, what else have they done? Glad you found the problem.
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Old 06-28-2020, 02:12 PM   #20
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Before you get too far into your remediation plan, flex the cables where accessible between the breaker and the main boat panel. The cable should be bendable. I would want to check for stiff sections from compromised insulation or strands fusing together. Might be worth disconnecting the wires at both ends and doing a resistance test with an ohm meter.

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