PO re-wired shore power

PO re-wired shore power from a 50 amp two circuit system to accept a 30 amp shore power with an adaptor to the 50 amp boat service. I guess he just had 30 amp at his dock and wanted to be able to run systems from both circuits. I am trying to figure out how he did it and how to reverse what was done. Any ideas?

50 amp 240V supply is wired this way:

The shore power supplies 240V and has 4 wires: two hots, a neutral and a protective ground. When you measure between the two hots you get 240V and when you measure between one hot and neutral you get 120V.

The 50 amp 240 V service will be wired to a main breaker that trips both hots. Then downstream of that breaker each hot will feed separate 120V busses with individual breakers that supply the loads. That assumes no 240V loads which your post seems to imply.

I haven't a clue what the PO did. He may have installed a 30 amp 120V circuit and wired the single hot to the two 120V busses. I suggest you trace the wire from the incoming shore power inlet to the main panel to figure it out.

David

David, thanks for your reply. If you did this to your boat,I assume you would do it in such a way as to make it easy to undo. Would just connecting the two hots at the distribution panel work for that purpose?

Is there a jumper wire connecting the two buss bars? With your 50amp svc. one black lead would go to one buss and the other one to the other buss. If the PO "rewired" with a 30amp cord, you would have only one black lead thus the jumper. If the original 50 amp cord is still installed (with some funky adapter to a 30amp at the shore power end) then only one of your black leads will likely be hot unless he combined then at his plug modification.

Pictures of the PO's adapter and/or your buss bars would help. you can also run ohms checks if you think he has connected both black leads. MAKE SURE you are unplugged from shore power and batteries off before you start poking around if you are not absolutely sure of what you are doing.

A marine electrician could fix you up in less than an hour if you aren't comfortable with this.

I have not gotten that far yet. The PO died so I can't ask any questions. The PO had a 30 amp cord with a 30 to 50 plugged into his home dock. He also had a regular two phase 50 amp cord. When I tried plugging the 50 amp in, the shore power trips. When I plug the 30 amp with adaptor everything work but I only have 30 amps. The boat has a 12 kW gen set so it needs a 50 amp shore power. I also checked the 50 amp cord and all is good with it. I like the idea of shutting it all down and using the ohm meter between the two hots.

Ah...a brain teaser. Is your power cord hard wired to the boat? I'm assuming that it is not as you mentioned trying the 50amp cord. Was the PO using a 30/50 adapter at the boat then as well? Did he rewire the plug at the boat to a 30amp plug.

The fact that the breaker tripped when you plugged in to 240V 50 amps is a pretty good indication that the two hots are jumpered at the main panel.

David

That's what I'm thinking as well since he was only pulling the one leg from the 50a and still had service throughout the panel.

Assuming the two hots are jumped at the distribution, will just disconnecting the jumper revert back to the original 50 amp two phase? Or should I look for something else?

Anything is possible.

My 50 runs both busses off a 30 Amp adapter I bought.

No jumper or anything unusual behind the panel.

But if it trips a 125/250 shore breaker using a 50A 125/250 cord, I am guessing something out of the ordinary was done and not well labeled.

I have seen panels where there is a circuit breaker to combine the 2 busses...not sure if it meets ABYC now.

psneeld said:

Anything is possible.

My 50 runs both busses off a 30 Amp adapter I bought.

No jumper or anything unusual behind the panel.

Click to expand...

PS Sound like my system but your electrical works with either the 50 or 30 amp. I may need professional help.

"I may need professional help"

It's probably cheaper (and safer) than running the risk of cooking something or someone. Never know what may have been done by the PO and that's always risky.

Good luck.

jwilsail said:

PS Sound like my system but your electrical works with either the 50 or 30 amp. I may need professional help.

Click to expand...

Depends on a few things whether you need much help.

Pictures of behind you panel may be a start.

But as has been suggested, there should be no direct wire between the metal strips that connect your breakers....or a wire that goes from one breaker to the metal bar on the other buss would be the connector. Which will work but must be off when using a 50A 125/250 cord.

If it's not obvious....and you still find yourself scratching your head...you might not need a pro electrical guy if someone familiar with boat wiring is willing to take a look.

Was the boat surveyed between you and the PO?

If so, ask him/her....explain what is going on and see what they say.

If you find something obvious, something I/you feel surveyors should catch....I am sure some of us would love to know.

psneeld said:

Was the boat surveyed between you and the PO?

If so, ask him/her....explain what is going on and see what they say.

If you find something obvious, something I/you feel surveyors should catch....I am sure some of us would love to know.

Click to expand...

The boat was surveyed and no mention was made. He referred me to a mechanic that worked on the boat but he did not know.

I think that when I find it, it will be a Simple fix. The PO did a lot of electrical work on the 12v system and had installed a heart inverter/charger with three battery banks.

Another possible clue is the Norcold refrigerator is not cooling. The ligtcomes on and you can hear what sounds like the compressor trying to come on. My thought is it does not like the power.

You should invest in professional help that is willing to let you watch and learn from them as they work.

I will get a professional. I will post the results of that.

After you have someone undo the wiring, the simplest solution is to keep the 240/50 socket at the deck. And the 240/50 power hose for fancy places.

Then a modified 120 plug adapter can bring the 120V using the lighter 120/30 power hose.

The adapter would be the place where the red and black are joined.

This is common RV practice , but RV style plugs don't fit boat plugs and sockets.