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post #7 of Old 02-07-2019
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Re: Fried Shore Power

Originally Posted by Ed Kinney View Post
Dearest Sailheads,

My shore power deck connection is fried. See pic.

Can anyone tell me how this could have happened? Shouldn't the dockside or onboard circuit breaker have tripped before the connection melted down?

It's 30 amp and 125 v and has been plugged into shore power for about half of the 5 years it's been installed.

Thanks in advance!


How it could have happened? One of the conductors (prolly the ungrounded by the look of it) developed an "intermittent" connection, which then began to arc and create carbon, which continued to increase the "closed" circuit connection impedance. Eventually, the impedance and resultant voltage drop became high enough that for the load current, sufficient electrical energy was converted to heat, to melt and burn the plastic.

Why the breaker didn't trip? The total circuit impedance was low enough that the current through the high impedance connection, was lower than the breaker rating. In your case, the breaker would not trip if 30 A was sustained forever. However, if 50 Vac was dropped at the high impedance shore power connection, that's 1500 W, certainly way more than enough to melt plastic. Under normal circumstances the voltage drop across a shore power connection should be less than 1 Vac.

It is wise to check cords and connectors after every use for signs of discolouration. At first sign, investigate, as just a slight discolouration may be due to actual burning on the other side.

Also investigate any case of low AC Panel voltage reading. If it is normally 120 Vac, and today it is 108 Vac, ensure it is not because of a bad connection.

Shore power connectors have an ALF (Average Life Expectancy) of about 15 years, and cords about 5.

Last edited by boatsurgeon; 02-07-2019 at 02:48 AM.
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