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Old 24-09-2007, 06:17   #1
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Shore power question

I'm afraid this question will give away my total ignorance of electrical systems but....
I just got a 12 year old Hunter with two shore power inputs. Both are marked 30A 125V and there is a "Y" connection that allows a single shore power input to be connected to both There are A and B busses on the main panel. So, here's the question: At the dock there are two connections, 30amp 125 and 50amp 120/240. If I have both A and B busses connected via the splitter should the dock end plug into the 30, the 50 or does it matter?


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Old 24-09-2007, 06:33   #2
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I think if you look at the plug (male), of the splitter , it will only fit the 50 amp socket, or at least indicate where it fits they will not fit both, either 30 or 50.. As the 50 amp plug is wired differently than the 30 amp plug is, and is a different size and configuration. The 50 amp plug has two hot legs (red and black) and the 30 only one.

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Old 24-09-2007, 06:53   #3
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Aha! Well, I looked at this for all of 3 minutes so you may be absolutely correct. I was thinking the Y went from the two boat connections to a shore power cable but it may be that it goes from the dock connection and then I need two separate shore power cables, one for each of the 30a inputs on the boat. Gotta check later today so as to ask the right question. Thanks!
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Old 24-09-2007, 09:27   #4
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The two 30 amps circuits have wires good to carry 30 amps, so in case of a short between the shore power and the on board AC breakers, the shore breaker would provide protection for the wiring.

If you use a cheater for the 50 amp breaker either a y type that has two 30 amp plug ins or 1 30 amp plug in your wiring between the shore power and the AC breaker would not be properly protected in case of a short (as above).

The two wire system I think is supplied since lots of smaller marina's have a limited number of 50 amp services but lots of 30 amp services, so you can get enough power to run air, washing machines etc, and charge your batteries.

If you get stuck with a 50 amp instead of two 30's though you don't have full power, or protection.

I would think that that the manufacturers could run two 50 amp suppplies, ran than 30's then you could safely cheat down to 30 amp shore power, or just go 50 amp.

Believe it or not most of the boats I have chartered came with cheaters so you could plug in to either 30 or 50 amps, when asked the charterer said yup go for it works fine.
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Old 24-09-2007, 10:43   #5
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You say you have two (2) 30A shore power inputs. Fine. That is common with one circuit providing power to air conditioning and the other to house power. Regardless, you have two inputs.

There are 1 x 30A to 2 x 30A adapters and 1 x 50A to 2 x 30A adapters available. The "male" side (that goes to the dock) are not interchangeable, so you have to work really hard to mess up (*story below).

If you have a 1 x 30A Y you can draw a total of 30A from the dock (protected by the dockside circuit breaker) regardless of distribution between the circuits on your boat.

If you have a 1 x 50A Y you can draw a total of 50A from the dock (protected by the dockside circuit breaker) with no more than 30A on either circuit on your boat (protected by whatever you have on your boat).

At most West Marine stores there is a big sign over the shore power section that shows all the different connectors for various voltage and current ratings. I suggest you go stare at that. <grin>

Story -- about three years ago I sold a boat with delivery from Occoquan VA to Haverstraw NY as part of the deal. The new owner's wife, trying hard to help, managed to get a 30A shore power cord shoved into a 50A dock power connector. *Boom*. Fortunately I had the shore power breakers on the boat turned off and all the new owner had to do was replace the power cord. The shore-side connector was really melted.

If it doesn't fit, look at it and figure out why. Don't force things.
S/V Auspicious
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