50A 250V/125V Shore Power to 30A 125V Boat

[Jonlove]

Hi All,

My 44ft Morgan Catalina has an inlet for power that is a standard 30A 125V twist lock fitting.

The shore power pedestal has a 50A 250V/125/V plug. Can I use this adapter: https://www.conntekisi.com/ss2-50p-t...igtail-adapter
?

The guy at the marina here tells me that the voltage will still be 250V and/or that this would still allow 50A to go into the boat without tripping the breaker which would be dangerous.

I had this hooked up before, and the boat was working, but the female plug on the cord shorted out and got charred.

I have looked online and not found an answer!

[Jammer]

Can you use it? Sure. Will it do what you want? Yes, if your boat is wired correctly and the marina's pedestal is wired correctly.


If the marina's pedestal is wired properly, there is both 125v and 250v available depending on which contacts are used. The adapter uses a pair of contacts that provide 125v.


The pedestal breaker, at 50a, would allow more current to flow than the adapter and your shore power cord and boat wiring could handle safely. But if your boat is wired correctly and to modern standards, it will have a 30a breaker connected to the shore power inlet. Because of Kirchhoff's Law of Current the current will be the same at the boat as it is at the pedestal, and so the 30a breaker (assuming it's working and wired correctly) will provide suitable protection.


Separately, if the female plug on your cord is charred, it is likely that the shore power inlet on your boat is damaged and should be replaced since it could be a fire hazard. The female plug on the cord should be replaced also, or the entire cordset, if you have not already done this.

[jordanbigel]

I was in this exact situation 2 weeks ago - got this adapter which works fine.

https://www.marinco.com/en/p/121A/Pi...5-250V-Male-To

I also have a 30amp breaker for incoming AC, but I also have a Victron Multiplus set to limit shore power input to 21amps, based on research which says 30amp cords can't really handle more than 21amps safely. I had several burned up female cord ends and several melted shore power receptacles - I just made this adjustment to the Multiplus when I replaced the receptacle, shore power cord and started using this adapter. So far so good.

[rslifkin]

The continuous limit for a 30 amp cord should be 24 amps (80%). Going up to the full 30 is ok intermittently (for short periods), but unless it explicitly states otherwise, AC electrical shouldn't be run above 80% for long periods.



That's why you can buy an 1800 watt hair dryer, but only a 1500 watt space heater. The hair dryer fully loads a 120V / 15A circuit (fine for the few minutes you'd use a hair dryer), but the space heater is expected to run for hours, so it's sized to load the circuit to ~80%.

[Jonlove]

Thanks All!

Yes I have a 30 amp breaker on the boat, and it splits to 2 15A circuits inside, so I think I'm good with that.

Also the inlet to the boat has been replaced and the cord is new. I'm going to go ahead and hook this up.

If I have any issues I'll let you know.

Jon

[Jonlove]

Oh, as for setting the charger/inverter to only take in 21 to 24V... I have Xantrex Freedom 2080. Do you know if it could be set for the same?

[jordanbigel]

Originally Posted by rslifkin

The continuous limit for a 30 amp cord should be 24 amps (80%). Going up to the full 30 is ok intermittently (for short periods), but unless it explicitly states otherwise, AC electrical shouldn't be run above 80% for long periods.



That's why you can buy an 1800 watt hair dryer, but only a 1500 watt space heater. The hair dryer fully loads a 120V / 15A circuit (fine for the few minutes you'd use a hair dryer), but the space heater is expected to run for hours, so it's sized to load the circuit to ~80%.

I have heard the 80% max current number quoted before, but (for me) the deciding factor in choosing 70% was this quote from Mainsail.

Not saying that there is no room for differing opinions, but as a non-professional when it comes to electrical systems, I have to choose what to believe from whom, and so far Rod has not let me down (and as I suspect you know, has a reputation for being somewhat of an Oracle on this sort of stuff.)

I generally don’t recommend loading a NEMA L5-30 30A circuit to more than 70% of its face value rating, especially in the marine environment. This means approx 21A on a 30A circuit. If you want to push it to 80%, and feel safe about that, the number is 24A. As a marine electrician I do not feel safe about that with the 1938 NEMA L5-30 plug standard.

WARNING: If you want to push beyond a 21A load on a 30A twist-lock you are doing so at your own risk.


https://marinehowto.com/shore-power-...tplug-vs-1938/

[rslifkin]

Rod is definitely taking a more conservative approach which leaves more room for corrosion, etc. in a marine environment. I was going based on what the connectors, etc. are designed for and will handle if they're in good condition.

I'll also agree that I'm not a fan of the L5-30 for marine use. It's just not robust enough. The 50A twist lock NEMA SS-1 and SS-2 connectors are much better in that respect, as are the smart plug connectors.