How to wire a 50 amp shore power plug in the USA

[shimari]

I went back and looked at my notes. There has been two types of advice:

1. Connect the neutral at the output isolation transformer to boat side ground and you get 240v 'single-phase' at 60hz.

2. Do not connect the neutral to ground at the output of the isolation transformer and leave neutral floating.

The electrician I used here in the US thought #2 was the safest since I have double pole breakers. This, however, means I also need to make sure when we're at the dock that neutral isn't tied to ground. This is easy with the Mastervolt software. I've just opted not to use the inverter at the dock.

I am not qualified to opine on the pros and cons of either approach. I've just reported what we did under the guidance of an ABYC electrician.

From my layman's perspective, people and professionals seem to use the same terms in different ways which makes things far more complicated than it should be....at least for me.

[s/v Jedi]

Originally Posted by shimari

I went back and looked at my notes. There has been two types of advice:

1. Connect the neutral at the output isolation transformer to boat side ground and you get 240v 'single-phase' at 60hz.

2. Do not connect the neutral to ground at the output of the isolation transformer and leave neutral floating.

The electrician I used here in the US thought #2 was the safest since I have double pole breakers. This, however, means I also need to make sure when we're at the dock that neutral isn't tied to ground. This is easy with the Mastervolt software. I've just opted not to use the inverter at the dock.

I am not qualified to opine on the pros and cons of either approach. I've just reported what we did under the guidance of an ABYC electrician.

From my layman's perspective, people and professionals seem to use the same terms in different ways which makes things far more complicated than it should be....at least for me.

No, there is no need for anything to change when on shore power because the coupling is an electromagnetic field and on the secondary side of the isolation transformer nothing changes.

With double pole breakers, yes the electrician is correct and a floating system is better and safer.

[donradcliffe]

You see 240 volts with a floating ground on the output of the isolation transformer. If you ground the blue wire of the output, all will be as it should be.

There is a similar situation with the 2000i honda generators. The ground will float until you tie it to the neutral.

[sailcrazy]

Following. Our Asia-built boat (230v, 50Hz) is now in the US(Puerto Rico). When we're on the dock/marina, we try plug into a 30amp. 110v power pole. If that's not avail, we use a pigtail to a 110v, 50amp power pole. Power comes into the boat, thru our isolation xfmr, and the boat sees 230v, 60Hz.....and everything works. However, we've had an issue with our shore power cords, in that the connection between the 2-50' cords(we need to use 2 of them), overheated enough to show...when we wwre plugged into the 50amp power pole. Could be corrosion at the terminals, rain getting in between the 2 plugs, or??. We saw no changes in the boat/electrical panel.

[s/v Jedi]

Originally Posted by sailcrazy

Following. Our Asia-built boat (230v, 50Hz) is now in the US(Puerto Rico). When we're on the dock/marina, we try plug into a 30amp. 110v power pole. If that's not avail, we use a pigtail to a 110v, 50amp power pole. Power comes into the boat, thru our isolation xfmr, and the boat sees 230v, 60Hz.....and everything works. However, we've had an issue with our shore power cords, in that the connection between the 2-50' cords(we need to use 2 of them), overheated enough to show...when we wwre plugged into the 50amp power pole. Could be corrosion at the terminals, rain getting in between the 2 plugs, or??. We saw no changes in the boat/electrical panel.

Try to use the 240V, using L1 and L2 terminals instead of 120V either L1 and N or L2 and N terminals. Set the transformer primary side to 230/240 if it is manual (some are automatic). Now you get the same 240V 60Hz out the transformer, but the input current is only half, eliminating most problems with the shore cable.

What kind of inlet and connectors do you have? The blue European style?

[GrowleyMonster]

So your Mastervolt inverter can accept a 120V 60Hz input, and convert it to the 230V 50Hz output that your boat is set up to use? Since you say it is phase independent and takes care of the conversion for you, I will assume that it is some sort of inverter and not just a simple isolation transformer. Well, in that case, if you don't need your big electrical loads like central air, electric water heater, electric cook stove, etc then the quick and dirty way is to simply use the ground and neutral, and only one hot, from the shore power. Be certain to properly insulate the end of the unused hot. Doesn't matter which of the two that you use. They are simply mirror images of one another, 180° apart in phase.

If connecting 240V 60Hz to your Mastervolt is indicated to be possible by your manual, then you need to be sure that if ground and neutral are not isolated from one another on the shore side, the unit needs to be capable of dealing with it. I NEARLY would assume that all you need to do is connect one shore power hot, the other shore power hot, and the shore power ground, to your MasterVolt inverter, and alles klaar und gut as they say in that place where they say that. If you connect that way, you probably need to keep the shore power neutral completely isolated from your boat though there may be provision for connecting it to your inverter's input.

If you connect only one 120V leg, then you only get half the maximum power at the boat end, vs connecting both legs. Might be enough. Might not.

Have you tried a phone call to the vendor or manufacturer?

Most REAL Marine Electricians understand the differences between the different voltage and frequency schemes and can keep you straight. If the one you hire thinks he does but does not, then there is someone to catch the liability or else just write a nice check in return for you not taking him to court. Once he has wired your pigtail then you are good to go with it at nearly every US marina, and a lot of marinas elsewhere that cater to US yachts.

Whatever wiring plan you end up with, be sure to post a good drawing and pic of it, for the benefit of others who come along after, asking the same question.

I strongly suspect that MasterVolt thought of this issue and allowed for it in the design, taking care that there is a straightforward way to do this, since it is a likely scenario for a customer to some day face.

What is the model number and unit name of your inverter?

[sailcrazy]

FWIW., Jedi...we watch the loads/amps on our boat elect panel, always keeping the boat load(at 230v) below 15-16 amps, so we don't exceed that 30amp(110v) load limit. The transformer is an auto sensing xfmr, that bypasses when connected to a 230v-240v source, and engages/transforms when the input is 110v. The shore power cords, boat inlet, and pigtail are all Marinco, not Euro std; when we sailed the Medd and Asia, we used a conversion adaptor., and had no issues.

[s/v Jedi]

Originally Posted by sailcrazy

FWIW., Jedi...we watch the loads/amps on our boat elect panel, always keeping the boat load(at 230v) below 15-16 amps, so we don't exceed that 30amp(110v) load limit. The transformer is an auto sensing xfmr, that bypasses when connected to a 230v-240v source, and engages/transforms when the input is 110v. The shore power cords, boat inlet, and pigtail are all Marinco, not Euro std; when we sailed the Medd and Asia, we used a conversion adaptor., and had no issues.

Yes, it’s clear now. So you have two issues:

- 30A through shore power cord instead of 15A
- Marinco 30A shore power components

The first one is addressed with my recommendation above: if at all possible, use the 240V terminals in the dock pedestal outlet. This is the one normally marked as 50A. This halves the current in the cables and almost all the problems will disappear.

The second one may come as a surprise to you, but you have the most hated and awful shore power inlet and cable system in existence. I recommend you modify this as follows:

1. Replace the boat inlet with the compatible SmartPlug version. This also requires a different connector on the cable at the inlet side and you can buy these as a conversion kit: https://defender.com/en_us/smartplug...-connector-kit
(of course sold out but someone will have it)

2. Replace the dockside plug with a 125/250 50A plug: https://defender.com/en_us/marinco-5...e-plug-6365crn
Connect green to green (GND), black to black (L1) and now it comes, white NOT to white but to red (L2).

This leaves you with two problems: how to connect to a 30A outlet when there is no 50A outlet and how to extend the length like you currently do with the 30A connectors that have bad contacts.

You can keep the 30A plug shore side and always use a diy made adapter from that to the 50A adapter. This is what I do. Now you can use a standard cable to extend. You can also switch to the blue Euro connectors and make adapters for both 50A and 30A outlets. I do that too, sometimes.
You get away with the 30A plugs in your cable because you are at half current, but when you connect to a 30A pedestal outlet then it’s 30A again and your 30A plugs are at risk. Luckily I find the 50A outlets everywhere so my problems are over.

There is another option; kind of a secret trick. I am assuming you have a Victron Multiplus or Quattro? If so then you can enable PowerAssist and limit shore power to 16A. If you do that then anything over 16A is taken from the battery instead of shore power. When your usage goes under 16A again, the battery gets recharged. This of course only works when you have periods where you use less than 16A.

[Andrew Lippman]

I am not sure why this is so complicated. The Mastervolt guide shows the appropriate wiring for US and EU 230/240v connections. Shore neutral is not used.

I believe that in general one connects neutral to protective earth at the source of power. That is your transformer. The diagram shows that and my last boat did it. The whole point is that PE from shore never reaches your boat. I believe I also had residual current breakers on the shore inlet as well as after the transformer.

Note that double breakers are needed. Both your line wires are hot, each is at 110v with respect to ground.

My oven at home is similar.

[Andrew Lippman]

I wonder if using the cable you have will confuse future electricians. In the US, white is neutral. Wire is wire so there is no physical reason not to use it as a hot line. But a real cable would have four wires, with neutral wired and simply ignored at the Mastervolt transformer. Then your red and black would each be hot and wired to the paired breaker as such. Using a three-conductor wire meant for 110v is potentially confusing. Electricians rely on appropriate use of the colors, I'll bet...

[GrowleyMonster]

Originally Posted by Andrew Lippman

I wonder if using the cable you have will confuse future electricians. In the US, white is neutral. Wire is wire so there is no physical reason not to use it as a hot line. But a real cable would have four wires, with neutral wired and simply ignored at the Mastervolt transformer. Then your red and black would each be hot and wired to the paired breaker as such. Using a three-conductor wire meant for 110v is potentially confusing. Electricians rely on appropriate use of the colors, I'll bet...

Good electricians who want to remain live electricians, check the wires. Color proves nothing and it should not be relied upon.

[team karst]

Originally Posted by Andrew Lippman

……..Using a three-conductor wire meant for 110v is potentially confusing. Electricians rely on appropriate use of the colors, I'll bet...

Yes, in the US, white is used to carry current at earth potential. There is a demand to mark each end with color if it is NOT at earth potential. Old school use tape. Modern school uses black or red sharpie.