Electrical issues

[rjcaudle]

I am relative newbie with 34 ft 2006 monohull.

Located in New Bern, NC and with the recent cold snap I had the heat pump running as well as a space heater.

Breaker flipped when i turned on an appiance. Realized too much was being used and then used less.

However when I when to unhook shore power I noted and burned up wire at the outlet going into the boat. Several inches of wire was burned, one prong on the boat side was melted loose, and the power cord was charred black at one female inlet.

My question is: Why didnt the breaker on the dock pedestal flip prior to almost causing an electrical fire. Looked very scary to me and I want to learn from this experience and hopefully not burn down to the waterline in the future.

My plan is to run less stuff and once, or consider adding another 30amp inlet.

Would appreciate thoughts from smarter folks than I.

Thanks.

[transmitterdan]

It is a common misconception that electrical fires can be prevented by circuit breakers. That is not the function of a circuit breaker. A circuit breaker will trip only when the current through the breaker exceeds a preset maximum amount. Typically most breakers will trip based on current and time. The higher the current the shorter the time before the breaker will open. Below some level the breaker will not trip at all.

In the case here the current through the breaker no doubt did not increase beyond the trip point. In fact, the current probably decreased as the connector got hotter and hotter which usually increases resistance. Increasing resistance means lower current.

There is a new shore power inlet connector for boats that includes a temperature sensor which should help to prevent these kinds of problems. If the connector gets too hot it should open and shut down the source of heat.

Regards,
Dan

[mitiempo]

I agree. I have changed 3 shorepower inlets recently that were burned and this is a connector that is a much better solution.
SmartPlug 30 Amp Marine Inlet and Connector

[boatpoker]

My shore power cord is hard wired into the boat, six fewer connections and much more reliable than a plug.

[mitchbrown]

Its likley that the problem was caused by salt water getting into the plug. If you ever drop the plug into the water you need to soak it in fresh soapy water for awhile and then rinse it really good before trying to use it again.

Mitch

[sailingdog]

TransmitterDan's probably nailed it. The breaker will only trip if the current draw exceeds its rating... the amount of current drawn has nothing to do with the amount of current needed to smoke and burn the wiring due to high resistance and bad contacts at the socket.

I'd highly recommend making the upgrade Mitiempo suggest, and have upgraded several boats, including my own, to the same system. One advantage that the Smartplug has is a thermal protection circuit that kills the power if the temperature rises at the shore power connector.

BTW, you're very, very lucky you didn't lose your boat to a fire...

@Boatpoker--

Yes, you have six fewer connections, but your shorepower cable is exposed to the elements far more as a result.

[lancelot9898]

Originally Posted by sailingdog

TransmitterDan's probably nailed it. The breaker will only trip if the current draw exceeds its rating... the amount of current drawn has nothing to do with the amount of current needed to smoke and burn the wiring due to high resistance and bad contacts at the socket.

I'd highly recommend making the upgrade Mitiempo suggest,

Bad contacts at the socket is the cause for the high resistance and while the new plug and socket has a thermal protect device which is good the root cause is still not addressed. Maybe that new design has a better connection not having the L shaped blade and a better locking mechanism?? Anyway a tight connection is of upmost importance and with the number of burned out plugs and resulting fires one would think that more effort would be put into the solution.

[boatpoker]

[QUOTE=
@Boatpoker--

Yes, you have six fewer connections, but your shorepower cable is exposed to the elements far more as a result.[/QUOTE]

I don't see how. The cord goes into the locker where the junction box is when not connected to shore.

[sailingdog]

Originally Posted by lancelot9898

Bad contacts at the socket is the cause for the high resistance and while the new plug and socket has a thermal protect device which is good the root cause is still not addressed. Maybe that new design has a better connection not having the L shaped blade and a better locking mechanism?? Anyway a tight connection is of upmost importance and with the number of burned out plugs and resulting fires one would think that more effort would be put into the solution.

The SmartPlug has a lot more contact surface area than the old twist-lock 30 amp connector design. More importantly, it also has a much more robust locking design that does not rely on the electrical connector pins to lock...

[rjcaudle]

I really appreciate all the comments, very helpful. By the way my plug to my knowledge has never fallen into the water.

After SailingDog's comments, I am concerned even more. How can it be that easy to start an electrical fire? With so many boats using shore power, it seems very likely this will be a recurring problem.

I'm now getting an electrician involved and considering installing the SmartPlug unless he has a better solution.

Thanks again for the help.

rjc