question about shore power wiring

[jim rosenthal]

All my electrical repairs to date in boating have had to do with replacing or repairing what was already in place. New inlets, new shore cables, that kind of thing. I don't pretend to understand the ins and outs of how shore current is supplied to boats, or wired. Hence this question.

One of my friends has an older Hatteras like mine- not the same model, but similar in the sense that his boat, like mind, has two 120vac 30 amp inlets- one for the ship's service, and one for the AC. He mentioned to me the other day that he was planning, at some point, to have the boat rewired with fifty amp 240vac service.

So I asked, "wouldn't that just give you 25 amps each on two 120vac lines? You'd actually have less amperage coming into the boat, on each line, than you do now. Right?"

"No," he said, "I'd have fifty amps on each 120vac line coming in. That's why I'd have it done."

Obviously, I know very little about AC wiring- just enough not to have set my boat on fire. But I would like to know from Krush, or Scott, or whoever wants to chime in, about this. Maybe I should already know this, and maybe it's a stupid question, but it seems to me that the stupidest question is the one that doesn't get asked, because a chance to learn is passed up.

I am also assuming that the 240vac cable has four terminals on it, total- two hots, a neutral, and a ground.

If converting to 240vac 50 amps gives two 120vac legs with fifty amps on each, I, too, would make this conversion on my boat.

 

[Walter P]

Good points Jim, I also am under the impression that a 240V 50 amp service when split gives you 120 volts AC and still has 50 amps per leg. Stuff like this is why when I need electric work done I call my friend Alec...Trician.

Walt

 

[jim rosenthal]

Thank you. Needless to say, I will not attempt this myself.

Also, if my boat is updated and has one 50A 240vac shore inlet, what do I use to connect it if I am at an older marina that only has 30amp inlets?

 

[Avenger]

Right, 2 X 50A as long as they're on opposing phases.

You'll need a Smartplug to put two 30s together to feed it and avoid problems.

 

[jim rosenthal]

Thanks to all. I am going to look into this. I have always had trouble making room for 2 thirty-amp cables- this would cost some, but it would make traveling a bit easier.

Is there such a thing as a 30A-50A adapter which just feeds one of the 120 vac legs? My home dock has only one 30A line.

 

[Avenger]

Yes adapters are available. If you're doing this conversion talk to boatsb. He offers a circuit breaker setup that could replace the other 30A socket. It makes for a nice, clean retrofit and circuit protection all in one.

 

[doc g]

Actually you still have 120 v 50 A on each leg even if the hots are not on opposing phases, you just don't have 220 V when combined if they are on not on opposite phases.....Pat

 

[jim rosenthal]

Yes adapters are available. If you're doing this conversion talk to boatsb. He offers a circuit breaker setup that could replace the other 30A socket. It makes for a nice, clean retrofit and circuit protection all in one.

How do I find out about this, Scott?

 

[Boatsb]

I'm traveling until monday. I have a parts list and all that info back at bome.

 

[Avenger]

Actually you still have 120 v 50 A on each leg even if the hots are not on opposing phases, you just don't have 220 V when combined if they are on not on opposite phases.....Pat

That's true. But you run into problems with the neutral if you're using same phase.

 

[davidwigler]

Amps x volts = watts

You presently have 30 amps at 120 or 3600 times two is 7200 watts.

50 amps at 240 volts is 12000 watts. Quite an improvement.

 

[krush]

That's true. But you run into problems with the neutral if you're using same phase.

THIS! If using the same phase, the single neutral will be carrying 100 amps. It's not designed for this.

This is for AMERICA
There is 30A 120V: 3 wires (hot, neutral, ground) and a single pole breaker
There is can also be 240V (with 30 or 50 or watever amp) that has 3 wire (hot, hot, ground), 2 pole breaker
Then there is 50a amp 240V/120V that has 4 wires (hot, hot, neutral, ground), 2 pole breaker

For the last one, 240/120, the 240V loads connect hot to hot (goes through both 50amp breakers). For the 120V loads, the load uses one hot (A) and the neutral (current only goes through 1 breaker). 120v load on the other hot (B), go through the other breaker and into the neutral.

Here's the kicker. If the 120v loads on hot A is 10 amps and the load on hot B is 10 amp, then (because of magic) there is no current flow in the neutral. The neutral only carries the DIFFERENCE. So if Hot A is using 15amp, and Hot B has no load, then 15 amp is going up the neutral too.

Don't you nit-pickers get on me about "flow" and "going up the neutral", it's just illustrative purposes only.

 

[Avenger]

To further elaborate, that is why I said you need a Smart Plug or Smart Y or whatever it's called when using two 30A services to power a 50A/240V. If they're on the same phase two 30s = 60 which is also too much for the neutral. The "smart" device has circuit protection for that.

 

[Avenger]

Don't you nit-pickers get on me about "flow"

Only if you start going on about the armature sprocket causing an interference with the flow and the dynaflow.

 

[SKYCHENEY]

Put in an isolation transformer. Then you can wire it with just hot, hot, ground with no neutral needed. You can also wire it with a switch to run off of one 50a 240v cord or off of one 30a 120v cord and still make 240v for any 240v loads that you may add to the boat. This Increases safety which I would think would be very important and gives you many options for power at different marinas.

 

[Pete]

First, you need to decide if the goal is to have two 125v/50a services or one 250v/50a service. Simply increasing the service on each 125 volt existing service from 30 to 50 amps is much simpler and far fewer $$$ that converting to 250 volt service.

Assuming the goal is two 50 amp 125 volt services, you need a new shore electric cable and a new 250 volt 50 amp connector on your boat. You then split that service off the back of the connector, update your wiring to #6 to the existing electric panels on the boat and install new main 50 amp breakers in each panel. Good idea to install a 50 amp fuse just behind the connector for the two hot wires.

Now for the marina with only 30 amp 125 volt service. Get a smart Y that has two 30 amp connections for the pedestal with one 250 volt 50 amp female plug for your shore power connector. This will solve two potential problems, first get electric service to the boat in such a situation and second protect the neutral in the power cord from overload, as if you connect both male 30 amp plugs to the same phase on the pedestal they do not work. You must be on opposing phases to activate the internal Y relay.

BTW, wiring as explained above eliminates any problems with marinas that used 208/3 phase wiring, something that is a pain for boats that are 250 volt wired.

Pete

 

[q240z]

I converted my CC Commander 42 from dual 30s to 125/250 50a. It's well worth doing...haven't popped a breaker since.

 

[DCMY #92]

Based on what's been said here, it seems that a non-smart reverse Y adaptor could be safely used when both 30 amp pedestal receptacles on the same phase as long as no more than 50 amps is permitted to flow through the neutral. If this is the case, would a 3 pole 50 amp breaker installed in the 50 amp lead of the adaptor (between female plug and Y) provide a safe solution?

 

[Pete]

One word answer on the triple ganged breaker which includes the neutral is yes.

Pete

 

[krush]

One word answer on the triple ganged breaker which includes the neutral is yes.

Pete

But does "code" allow it?