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Old 05-23-2016, 06:39 PM   #1
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50 amp 125 v

I have a 2005 34 mainship pilot. The boat plug is 50 amp 125 volts.. Can I convert the receptable. to 50 amps 250 volts
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Old 05-23-2016, 06:58 PM   #2
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Well, what is 50 amp service?

What exactly is your 50 amp, is this single phase 50 amp at 125vac?

Marina power for a 240vac plug likely will be 50 amp split phase 240vac.

If you study on this, then you can make that change, but power will be on alternate phases, so you may need a different circuit breaker distribution panel, or not. All that depends on what you actually have in the boat panel.

50 amp times 240 vac is 12000 watts of total available power.
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Old 05-23-2016, 08:17 PM   #3
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I have a 2003 Mainship Pilot 34 and it has a 30 amp 120V shore power inlet. If you really have a 50 amp 120V inlet, an oddball, then first check the wire size to it. It may be the same wire that is on my 30 amp service- 10 gauge and is not suitable for 50 amps. Also check the main A/C breaker. It is 30 amps on mine.

I strongly suspect that a PO replaced the receptacle with a 50 amp, 120V one for more robust life and used an adapter with it, but left all of the internal wiring and breakers sized for 30 amps. This won't meet anyone's electrical code, but anything is possible.

But if you really have 50 amp 120V inlet and the proper internal wiring and breaker size, then you can replace it with a 50 amp 240 volt inlet and just use one of the two 120V legs, ie black to neutral or red to neutral and leave the other leg disconnected.


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Old 05-23-2016, 08:23 PM   #4
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There were more than a few boats that left the factory with a 50A 125 service. Too bad as the dockside receptacle is pretty rare..nothing wrong with it...just may need an adapter...

But it is worth knowing for sure that your shore side matches what the boat can handle.

Electrical systems always seem to baffle sone boat manufacturers.
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Old 05-23-2016, 10:37 PM   #5
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Don't go crazy rewireing your boat. Get a Hubbell HBL61CM56 and HBL61CM72 adapter and you'll be able to plug into either 30 amp 125 volt or 50 amp 125/250 volt outlets.
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Old 05-23-2016, 11:09 PM   #6
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Parks, would you please explain that a bit further?


My boat has 50A/125V and 50A/240V. Each runs different areas of the boat as far as what equipment it powers. The 125V runs all the lights and things like the refrig/freezer, coffee maker, receptacles, etc. The 240V runs the heat-A/C units, stove, water heater, etc.


I'm confused about how he could plug into either 120V or 240V and be safe.


Non-Electrician GFC
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Old 05-23-2016, 11:28 PM   #7
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I'm not an electrical expert but as I understand it the 250 volt that is common in the US is made up from two 125 volt legs. The adapter simply takes power from one of the legs and delivers 125 volts to the boat. I think he would only be able to pull 25 amps from it but someone smarter than me can address that.
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Old 05-24-2016, 07:04 AM   #8
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Electrical question.

This discussion may clear up the amps per leg question.
If you have a dual pole 50 amp breaker, then each leg is rated for 50 amps, but since the current alternates up and down, you can never get 100 amps on the load side. The sine wave passes through a central zero point and the peak is equal on each side plus or minus.

Alternate phases also alternate current on the source side 180 degrees out of phase one with the other. So the voltage flow is up and down in a sine wave pattern 180 degrees with another voltage flow up and down. If they were superimposed one on the other, it will short out. Just join two out of phase black wires and sparks will fly.

Each pole on a double pole breaker carries 125 vac 180 * out of phase with the other pole. Each leg can supply 50 amps. But this is not additive to 100 amps when using the double pole breaker to supply a load with 240 vac. The total wattage of the available power does not double, the VA must remain constant. ASFAIK this is how it basically functions.
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Old 05-24-2016, 07:20 AM   #9
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I'm not an electrical expert but as I understand it the 250 volt that is common in the US is made up from two 125 volt legs. The adapter simply takes power from one of the legs and delivers 125 volts to the boat. I think he would only be able to pull 25 amps from it but someone smarter than me can address that.
Parks wins the prize!!! That's exactly what the adapters do and they are completely safe to use. And you will get the full 50A@120V. It's rare one gets such a straight forward solution to a problem.
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Old 05-24-2016, 07:24 AM   #10
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Originally Posted by sdowney717 View Post
Electrical question.

This discussion may clear up the amps per leg question.
If you have a dual pole 50 amp breaker, then each leg is rated for 50 amps, but since the current alternates up and down, you can never get 100 amps on the load side. The sine wave passes through a central zero point and the peak is equal on each side plus or minus.

Alternate phases also alternate current on the source side 180 degrees out of phase one with the other. So the voltage flow is up and down in a sine wave pattern 180 degrees with another voltage flow up and down. If they were superimposed one on the other, it will short out. Just join two out of phase black wires and sparks will fly.

Each pole on a double pole breaker carries 125 vac 180 * out of phase with the other pole. Each leg can supply 50 amps. But this is not additive to 100 amps when using the double pole breaker to supply a load with 240 vac. The total wattage of the available power does not double, the VA must remain constant. ASFAIK this is how it basically functions.
Yes, that's all correct too. As for 120V loads, you can't place any more than 50A of loads on any one "leg", but if you are able to split your loads up between the two legs, which is how a North American electric panel is wired, you can power a max of 100A of 120V loads (50A worth on each leg).
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Old 05-24-2016, 07:38 AM   #11
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Twistedtree is correct that 100 amps 120v is available...but only 50 amps 240....

Depends on how the boat is wired....mine is a 3 pole breaker feeding 2 120v busses. If I wanted 240 appliances I would have sub-panel wIred with a 2 pole breader and 2 hot 110 legs. But it could have been wired to a 240 main panel. Then a 110v panel could be run off one 110 leg.
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Old 05-24-2016, 08:00 AM   #12
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Since this is a split buss, split phase, even though you can get 100 amps total at 125vac from a 50 amp 240 vac service, you can never get more than 50 amps 125 vac for any single circuit, as you have 50 amps on one leg and 50 amps on another leg.
And you can not combine the legs or sparks will fly.

So if you had a device needing 75 amps of 125vac power, you could not power it.
Yet you could power two 50 amp devices since each side of the breaker can give 50 amps, so a total of 100 amps power available. But you can not use more than 50 for a single device or a group of devices, or the breaker will trip.
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Old 05-24-2016, 08:40 AM   #13
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We got the Hubble and it works great. We mostly got it because some places only have 30amp service and we have a 50 amp setup. It's a SMART device so know rewirework is necessary all plug n play.
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Old 05-24-2016, 08:54 AM   #14
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We got the Hubble and it works great. We mostly got it because some places only have 30amp service and we have a 50 amp setup. It's a SMART device so know rewirework is necessary all plug n play.
He doesn't need a smart Y if he truly had a single 50a 125 cord.

With a single leg 50a 125 cord you only have 1 leg of 125v. You can either adapt to a single 30a outlet or adapt yo use 1 leg of a 2 leg 50 a 240 outlet.

A smart Y is only necessary to plug into say two 30a outlets to feed your 50a 125/250 cord. The smart Y makes sure the phasing is correct at the outlet.
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Old 05-24-2016, 08:57 AM   #15
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Since this is a split buss, split phase, even though you can get 100 amps total at 125vac from a 50 amp 240 vac service, you can never get more than 50 amps 125 vac for any single circuit, as you have 50 amps on one leg and 50 amps on another leg.
And you can not combine the legs or sparks will fly.

So if you had a device needing 75 amps of 125vac power, you could not power it.
Yet you could power two 50 amp devices since each side of the breaker can give 50 amps, so a total of 100 amps power available. But you can not use more than 50 for a single device or a group of devices, or the breaker will trip.
Thanks...I won't buy anything that needs 75 amps....

Plus my main tech man sent me this link....

Single-phase Power Systems : Polyphase AC Circuits - Electronics Textbook
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Old 05-24-2016, 11:48 AM   #16
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I have a 2005 34 mainship pilot. The boat plug is 50 amp 125 volts.. Can I convert the receptable. to 50 amps 250 volts
I would buy an electrical adaptor cord exstentio rather the change boat plug as each marine might be different. Our boat plug is 50 amps 120 volts, so we have an adaptors for 30 amp 130 volts and 50 amps 240 volts depending on the shore power. Much easier to use adaptors and saver.
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Old 05-24-2016, 01:05 PM   #17
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Thanks...I won't buy anything that needs 75 amps....

Plus my main tech man sent me this link....

Single-phase Power Systems : Polyphase AC Circuits - Electronics Textbook
Just being extreme as a way of helping to understand how it works.
None of my loads are bigger than 20 amps, I suppose the Princess stove-oven does have a 30 amp breaker with 10 gauge wire.

15 amps,1600 watt microwave is right at that level, used a lot.
11 to 12 amps for heat pump.
Hot water heater, 12 gallons, around 13 amps, I think, really never turn it on.
Two small electric wall heaters maybe 7 to 8 amps each, never get any use.

My boat uses twin 30 amp 125vac cords. I almost never will plug in the other cord. My marina gives us free power on a 30 amp breaker with a 20 amp plug. Of course my Marinco adapter is the standard 15 to 30 amp style.

I did setup a 30 amp two pole switch to join two 30 amp lines to function off one 30 amp cord for convenience sake, after my own 2 pole 30 amp on the boat breaker. I have never tripped it. That way my split system, all the devices can run off one cord to one dock plug. I don't typically use more than 20 amps at any time from the dock, usually around 11 to 12 amps, of I turn on the AC.
All the time, the boat uses from 1 to 1.6 amps. The fridge takes about 1.1 amps, remainder is the battery charger.

I have dual AC voltage and AC amp digital gauges on each line. And a single Volt-Amp digital gauge for the DC house loads.

I found these digital gauges highly accurate. The AC uses a sense coil, the DC uses a shunt in the common ground return for the house batteries.
I have 3 switches controlling 4PDT 35 amp power relays, so I can turn on inverters, gens, shore power, with some indicator LED lights. And this small panel also displays reverse polarity using red neon lights.
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Old 05-24-2016, 04:42 PM   #18
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Since this is a split buss, split phase, even though you can get 100 amps total at 125vac from a 50 amp 240 vac service, you can never get more than 50 amps 125 vac for any single circuit, as you have 50 amps on one leg and 50 amps on another leg.
And you can not combine the legs or sparks will fly.

So if you had a device needing 75 amps of 125vac power, you could not power it.
Yet you could power two 50 amp devices since each side of the breaker can give 50 amps, so a total of 100 amps power available. But you can not use more than 50 for a single device or a group of devices, or the breaker will trip.
Yes, that's exactly right. People will sometime quibble over whether you have 50A or 100A @120V, and it's because of exactly this. With perfectly balanced 50A loads on both legs, you can service a total of 100A @120V. But no single load can be more than 50A, and they need to be perfectly balanced. Imbalances are fine, but reduce the total power that you can extract out of the circuit.
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Old 05-24-2016, 08:10 PM   #19
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I have a 2005 34 mainship pilot. The boat plug is 50 amp 125 volts.. Can I convert the receptable. to 50 amps 250 volts
With an adapter, yes. If you're talking about changing the boat's electrical inlet or any wiring changes, you should have it done by a licensed marine electrician.
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