50A to 30A shore power adapter question

[Shankara]

Hello all,

I have my eye on a better spot on the dock in my marina, although the power pedestal is 50 A/250 V, and my boat’s electrical system is 30 A/125 V.

I purchased a Marinco pigtail adapter, 50 A 125/250 V plug at Dock - to 30 A 125 V connector to Boat.

Does anyone know if this adapter is ok to use for my shore power hookup? My worry is that my lack of knowledge may case damage to my battery charger or something else.

Thanks,
Shankara

 

[Slick470]

the 125/250V side is 4 wires; L1, L2, N, G and the 125V side is 3 wires; L1 (or L2), N, G. On the 125 side, it's just skipping one of the hot conductors that lets you get to 250V. Nothing wrong with that.

The part that is a bit wonky is your boat's 30A main breaker should protect (and limit) your boat side load to 30A @ 120V, but the shore power receptacle is protected at 50A @ 240V. So there is a section of wiring from your main breaker to the adapter that is rated at 30A @ 120 but is protected by the power pedestal circuit breaker at 50A @ 240V. This wiring is now technically undersized for what is protecting it. Now this shouldn't be an issue since your main breaker is limiting the load that this wiring will see, and Marinco wouldn't make these adapters if they violated some rule, but it is something to keep in mind.

I would also ask your marina if using this type of adapter is allowed. Some marinas don't like them.

 

[jtsai]

Hello all,

I have my eye on a better spot on the dock in my marina, although the power pedestal is 50 A/250 V, and my boat’s electrical system is 30 A/125 V.

I purchased a Marinco pigtail adapter, 50 A 125/250 V plug at Dock - to 30 A 125 V connector to Boat.

Does anyone know if this adapter is ok to use for my shore power hookup? My worry is that my lack of knowledge may case damage to my battery charger or something else.

Thanks,
Shankara

I have used such adapter at a marina with only 50 amp electrical supply for a year without problem.

 

[gareth harris]

Unless you already have a transformer onboard then plugging 250V into a 125V system will fry things.

Whether it is 50A versus 30A is irrelevant to whether or not you can plug in, that is just the upper limit on the current available. It is the voltage that is important, and if 125V is not available at the new slip - which would seem odd - then a transformer with sufficient power rating for your likely needs will be essential. A typical mains outlet has a limit of 13A, but the critical question is how much power you will actually use at one time. If you have any heaters or hot water heater, or use electric cooking at the dock, then your needs may be quite high.

It is hard to know what to recommend without knowing what your electrical system already has.

Gareth
Freyja E35 #241 1972

 

[Nick J]

Unless you already have a transformer onboard then plugging 250V into a 125V system will fry things.

Whether it is 50A versus 30A is irrelevant to whether or not you can plug in, that is just the upper limit on the current available. It is the voltage that is important, and if 125V is not available at the new slip - which would seem odd - then a transformer with sufficient power rating for your likely needs will be essential. A typical mains outlet has a limit of 13A, but the critical question is how much power you will actually use at one time. If you have any heaters or hot water heater, or use electric cooking at the dock, then your needs may be quite high.

It is hard to know what to recommend without knowing what your electrical system already has.

Gareth
Freyja E35 #241 1972

@Slick470 does a good job explaining why you get 125V from a 50amp connection. No issue there.

It looks like 30amp cables are typically built with 10awg wire which is more than enough to meet the ampacity needs of a 30amp circuit. 50 amp cables are built with 6 or 8awg wire, so your 30 amp cable will technically be undersized. However, with the 30amp shore power breaker in the boat, you should never draw more than the rated ampacity of your 30 amp cable. The only realistic scenario where you would be at risk is in a short which would trip the 50 amp breaker in the pedestal anyway. I don't think there's a huge risk here.

 

[Slick470]

Other than the voltage change bit, this is effectively a "tap". There are various rules about taps in the National Electric Code that let you get away with "tapping" into a higher amperage circuit with lower ampacity conductors without overcurrent protection at the tap location. My guess is this arrangement meets the various provisions of whichever rule governs.

 

[Shankara]

Thanks so much everyone!!! You are all so wonderful. This is such a nice sailing forum!!!

The adapter seems to be doing what it is meant to do and I’m in a better spot!