Help me understand Shore Power

[Dsanduril]

Originally Posted by Muaddib1116

I'm at my boat doing some work, and I took a closer look at the back of the 50A 125/250 inlet and how it is wired to the ELCI box. The back of the inlet has 4 cable clamps: X, Y, W, Ground. A yellow wire with a green stripe is wired into the Ground clamp. A black wire is in the X clamp. A blue wire is in the W clamp. The Y clamp is empty. So the electrician has 3 wires going into the breaker box and presumably 3 wires coming out. ( I don't want to open up the back of the breaker box at this point. )

So if the X and W are the boys and the Y is the neutral, then there's 250V at 50A going into the breaker box and then into the isolation transformer. If the W is neutral, then there's 50A of 125V going into the breaker box. I can't seem to find a source that identifies the X, Y, and W.

This doesn't sound right to me either. The IEC/Euro standard is brown=hot, blue=neutral, green/yellow= PE ground. So far, so good if he used the original wires and what you saw as black is actually brown.

But the NEMA X-Y-W standard marking for US 240V is X=hot, Y=hot, W=neutral (since US wiring white=neutral the mnemonic for memory is W/white).

So, it seems your electrician has taken the European blue neutral wire and connected it to the US neutral/center tap of a 125/250 connector. That will then give you 120V between the X and the W. Which gives you 120V into your iso xfmr. Even though Euro neutral is blue, in this case you want to be using X and Y terminals on the US plug to get 240V into your iso xfmr. Big caveat - if the transformer has a step-up capability and he has configured it with a jumper - although I wouldn't understand why as you would then only have 120V 50A available at the xfmr inlet - might be OK if your boat service was 16A but doesn't sound like it.

[Muaddib1116]

So, I managed to grab the electrician for a few minutes and I think we're on the same page. The cables connected to the back of the shore power inlet were connected by the yard in NC when they replaced the burnt out inlet. They wired it to the neutral and 1 hot. The electrician here didn't check that and wired it into the new breaker box as 2 hots. So that will be fixed at the inlet.

The next thing is the new 50 amp breaker. He says the water damaged breaker that he replaced, that looked original (it matched all the other electrical components on the boat), was a 50 amp breaker. Interestingly, a wiring diagram that I found in the boat's build paperwork specs a 63 amp breaker there. The wiring is 3x16mm^2, which I think puts it somewhere between 5 and 6 awg. So, the mystery that we're trying to figure out is how is the 6kW isolation transformer protected. For the 50 amp breaker to flip, I would need to draw 12kW. What happens to isolation transformers if they are overdrawn? The limited spec info from Mastervolt just says that it has a nominal input amperage of 26 amps at 230V. That doesn't sound like a maximum. What happens when that is exceeded? Should we switch that new 50 amp breaker to a 25 or 30 amp breaker?

I found out the laundry machine model number, and it is a 50hz machine, so I'll need to only run it on the generator or inverter. The Cruisair ACs are rated at 208-230V~60hz or 200V~50hz, so I think they should be fine.

[Dsanduril]

Is the transformer the GI series with the nice cabinet and control panel? In which case there is internal overload protection and the transformer will shut itself down on overload.

Or is it one of the open models installed in a box by the boat builder?

Either way, transformers have a high inrush current and the protection on the primary (shore power) side has to be able to deal with this. In the US the codes allow input side breakers to be 125%-250% of nominal rating - if the secondary (boat) side has protection at 125% or less of the outlet capacity. The wires between that "oversized" breaker need to be rated for the breaker size, but the transformer itself can be rated for the lower current.

In your case 50A is probably acceptable (that's a little less than 200%), a 40A might work, although in that case a "D" curve circuit breaker would probably be more suitable (the curve describes how much inrush a breaker will allow, B=lower, C=typical and most common, D=higher). My personal preference, if I were designing it, would be a 40A D-curve. But, in the real world a 50A C-curve is probably fine as long as the wires are sized for that (sounds like they are).

[Muaddib1116]

Thanks Dsanduril, that's really helpful! Where am I supposed to find out this sort of info? Mastervolt's site isn't really helpful. The only specs I could find about that were the nominal amperage.

My transformer is the IVET 6, not the GI Series. It's in a pretty large metal box that looks like it was made by Mastervolt. Next to it is one of Mastervolt's Soft Start Transfer Systems, I'm guessing a matching 6kW. Mastervolt's site says that the Soft Start device suppresses the inrush current.

I think on the build drawings this is labeled as a Mastervolt Masterswitch. If that's the case, then the boatside of the Transformer as well as the Generator are wired into the Soft Start Transfer and then that is wired into the breaker panels for the 230V (Shore Power/Generator) equipment (AC's, watermaker, chargers, etc.).

Originally Posted by Dsanduril

if the secondary (boat) side has protection at 125% or less of the outlet capacity.

What do you mean by outlet capacity? From the isolation transformer into the boat, the next place with any sort of breaker is the breaker panel I mentioned above. Each device has it's own breaker, and the panel has a master breaker that is some sort of Siemens European breaker that's not a GFI, but something sort of equivalent. My electrician said they trip at 30mA or at 63A. I didn't really follow what he was talking about.

[Dave9111]

There are a lot of details in this thread, but I'm not sure I understand your goals?

Are you going to be venturing overseas so you need to retain the IEC wiring, or are you going to stay in 240/120V - 60hz land?

You need to develop a "big picture" or your needs otherwise you are going to remove stuff you will want later if you venture overseas.

If you are sticking to US standards, then you need to figure out what can run on 120/240 VAC at 60hz. And then figure out a game plan to make the changes.

If you need a dual system, then you don't want to rip out all of your IEC gear.

Using Smart Plugs vs not is details. You need a "big picture". The yard electricians don't get paid to supply the "big picture". They get paid to install and remove stuff.

[Dave9111]

---My electrician said they trip at 30mA or at 63A. I didn't really follow what he was talking about.


That's 30 ma of leakage current, as in a ground fault. (One hot leg leaking to earth ground) They don't call them GFCI's at that level of leakage current, they have another term for them which I forget. 63 amps is the current trip point of the breaker. More than 63 amps and the breaker will trip some time in the future depending on the breakers current curve.

[Muaddib1116]

Originally Posted by Dave9111

There are a lot of details in this thread, but I'm not sure I understand your goals?

Are you going to be venturing overseas so you need to retain the IEC wiring, or are you going to stay in 240/120V - 60hz land?

You need to develop a "big picture" or your needs otherwise you are going to remove stuff you will want later if you venture overseas.

If you are sticking to US standards, then you need to figure out what can run on 120/240 VAC at 60hz. And then figure out a game plan to make the changes.

If you need a dual system, then you don't want to rip out all of your IEC gear.

Using Smart Plugs vs not is details. You need a "big picture". The yard electricians don't get paid to supply the "big picture". They get paid to install and remove stuff.

My goal was mostly to learn. To learn more about what the shore power standards out there are, as well as relate that to what my boat needs and what the electrician did. I do have a good idea of what my big picture is, in regards to the shore power of my boat. And that is to be able to work with American shore power, and if need be European shore power. From what I've learned, this is mostly doable, with the existing system and the new ELCI breaker that was put in.

I think with the existing setup, I can run pretty much everything on my boat with either American or European shore power, with a couple exceptions that have workarounds. In the US, I'll use 50A 250V 60Hz service, and in places with European power I'll use 32A 230V 50Hz service. When I do eventually go somewhere with European power, I'll have to make an adapter that feeds the neutral and hot of their 230V to the two hots of my shore power cable.

I think Dsanduril mostly cleared up my last concern with the new ELCI box, which was the breaker amperage. I'm still not exactly sure what he meant about the boat side have protection of 125% or less of the outlet capacity. Hopefully he'll chime in and help me understand that last part

Originally Posted by Dave9111

---My electrician said they trip at 30mA or at 63A. I didn't really follow what he was talking about.


That's 30 ma of leakage current, as in a ground fault. (One hot leg leaking to earth ground) They don't call them GFCI's at that level of leakage current, they have another term for them which I forget. 63 amps is the current trip point of the breaker. More than 63 amps and the breaker will trip some time in the future depending on the breakers current curve.

Thanks Dave. I can't say that I understand that fully, but it sounds pretty close to what the electrician said. I think he said something along the lines of it not tripping as quickly as a GFCI, but being sort of equivalent in function/use.