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coot · 23-02-2006, 01:18

It's looking like you're going to spend a lot of time on electric. It could be worse -- I would rather work on electric than plumbing any day.

I assume what you're saying is this:

A bad 15 amp branch circuit shorted out. When it did, all your shore power went down. The 15 amp breaker in the panel did not blow. The 30 amp AC breaker in the shore power pedestal did not blow.

There is a 30 amp AC breaker between the shore power inlet and the distribution bus in your AC panel. (If there isn't, there should be!)

All you have to do is find it and reset it. If you think that you have found it already, look for another one closer to the shore power connector.

I think it is unlikely that you developed a new defect because of this event. A well implemented electrical system should be able to tolerate this kind of a fault without any damage. If you find a burned wire somewhere, it is important to ask: Why was it possible for this to happen, and what do I need to do to make my electrical system safe?

[ I'm not saying "don't inspect the wiring" -- just if you find anything, replacing the burned up part is not enough to fix the problem. ]

Here is a thing to think about with fuses and circuit breakers: The more overcurrent, the faster it reacts. 31 amps on a 30 amp circuit will take a while to get cut off. 35 amps will take a little less time. 100 amps will get cut off very fast.

Circuit breakers and fuses come in different speeds; the fastest one is the first to react.

In a normal 30 amp shore power connection, there is a breaker on the shore power pedestal and another in the boat. Normally only one of them will shut off for an overcurrent condition, because the other one will be a little slower. Where I'm docked right now, the breaker in the pedestal is consistently faster than the breaker in my internal wiring.

In your case, you had an instantaneous short circuit current of hundreds of amps. That triggered the fastest circuit breaker, and then all the slower circuit breakers saw the current drop to zero.

Your 15 amp breaker was too slow in responding. The 30 amp breaker shut the power off faster. If you just had a toaster and a hair dryer running at the same time, your 15 amp breaker would have responded.

23-02-2006, 01:18	#12
coot Registered User Join Date: Feb 2006 Posts: 367	It's looking like you're going to spend a lot of time on electric. It could be worse -- I would rather work on electric than plumbing any day. I assume what you're saying is this: A bad 15 amp branch circuit shorted out. When it did, all your shore power went down. The 15 amp breaker in the panel did not blow. The 30 amp AC breaker in the shore power pedestal did not blow. There is a 30 amp AC breaker between the shore power inlet and the distribution bus in your AC panel. (If there isn't, there should be!) All you have to do is find it and reset it. If you think that you have found it already, look for another one closer to the shore power connector. I think it is unlikely that you developed a new defect because of this event. A well implemented electrical system should be able to tolerate this kind of a fault without any damage. If you find a burned wire somewhere, it is important to ask: Why was it possible for this to happen, and what do I need to do to make my electrical system safe? [ I'm not saying "don't inspect the wiring" -- just if you find anything, replacing the burned up part is not enough to fix the problem. ] Here is a thing to think about with fuses and circuit breakers: The more overcurrent, the faster it reacts. 31 amps on a 30 amp circuit will take a while to get cut off. 35 amps will take a little less time. 100 amps will get cut off very fast. Circuit breakers and fuses come in different speeds; the fastest one is the first to react. In a normal 30 amp shore power connection, there is a breaker on the shore power pedestal and another in the boat. Normally only one of them will shut off for an overcurrent condition, because the other one will be a little slower. Where I'm docked right now, the breaker in the pedestal is consistently faster than the breaker in my internal wiring. In your case, you had an instantaneous short circuit current of hundreds of amps. That triggered the fastest circuit breaker, and then all the slower circuit breakers saw the current drop to zero. Your 15 amp breaker was too slow in responding. The 30 amp breaker shut the power off faster. If you just had a toaster and a hair dryer running at the same time, your 15 amp breaker would have responded. __________________ Mark S.