Help me understand Shore Power

[Muaddib1116]

Hi guys, my experience with shore power is limited, and my understanding of electrical systems is very basic. The boat I have sailed for most of my life has a very simple electrical system, and the few times we did go to marinas, we only needed to plug into the 30A shore power to run 3 120v outlets and the battery charger.

My new boat was wired for European use, and I bought it from the last owner who sailed it across at the end of 2019. There was some water damage to the shore power inlet and the breaker next to the inlet in the lazarette. I'm having the yard get that up and running, and I'm trying to educate myself about shore power for larger boats that actually use a lot of power. The yard put a new Marinco 50A 125/250V inlet in, and wired it into a Blue Sea ELCI 50A 120/240V breaker enclosure in the lazarette.

I'm confused about the term "50A 125/250V", which my googlefu has taught me is pretty standard in American marinas. What I can't find by searching the internet is an explanation for dummies (me) of what that is. I know it has 4 wires/contacts. So is it basically 2x 50A 125V wires, a neutral, and a ground, which can supply 2x 50A 125V circuits or 1x 50A 250V circuit (depending on how it's wired in the boat)? or is it 2x 25A 125V wires that can create 1x 50A 125V circuit or 1x 25A 250V circuit?

I have some follow up questions, but I think understanding what this is, should be my first step.

[s/v Jedi]

It is a 240V 50A (12kW) connection with a twist: the transformer that supplies this has a center tap on its output winding, which is the halfway voltage point. They ground that center tap and call it Neutral.

If you use 120V between L1 and N then you still only have 50A so 6kW. Between L2 and N you also have 120V and 6kW. One side can not exceed that even when the other side has room left. So 120V loads must be balanced.

[Dsanduril]

Originally Posted by Muaddib1116

....it has 4 wires/contacts. So is it basically 2x 50A 125V wires, a neutral, and a ground, which can supply 2x 50A 125V circuits or 1x 50A 250V circuit (depending on how it's wired in the boat)....

This is basically it. Both hot wires (125V above ground reference) can carry 50A. The neutral can also carry 50A. If you use 240V then only the hot wires are used and you can use up to 50A. If you are using 120V you have a total of 100A available, with 50A being the maximum single load.

You can also use some of both (30A of 240V leaves 20A of 120V available on each hot leg).

[Muaddib1116]

Great, thanks guys! I'm not sure I understood everything you guys said exactly, but I think I got the important part.

So what I'm wondering now is about how this joins in with the boat's existing setup, which I believe was setup for European shore power. My understanding is that Euro shore power is 230V 50Hz at 16A,32A,or 64A, with 3 wires/contacts. I'm not sure what amperage my boat was originally set for, I should have looked more carefully before they pulled out the old stuff.

The original setup was that the shore power inlet was wired to a waterproof breaker box in the lazarette (which was just replaced as I described previously). Which is then wired to an Mastervolt isolation transformer (230V) which goes into a Mastervolt Masterswitch (which I believe auto switches between shore power and the generator (240V), depending on what is providing power. Maybe shore power takes precedence if it is supplying power?

I was looking at the wiring schematic for the Blue Sea ELCI box.

https://d2pyqm2yd3fw2i.cloudfront.ne.../980009860.pdf

And if the output is also the 4 wire setup, how does that link up to the existing wiring that leads from my lazarette to the isolation transformer, which must have been the 3 wire European setup? Or is there another way to wire the Blue Sea breaker so that 4 wires go in and 3 wires come out?

PS. Despite my mechE degree, I know I sound like a child when talking about electricity.

[Dsanduril]

Are you leaving the boat itself Euro, not planning to use any 120V gear? You/your equipment are OK with 60Hz on shore power and 50Hz on generator?

[Muaddib1116]

There are 120V outlets that run off of a 120V inverter, and 230V outlets and a 230V washer/dryer laundry machine that run off of a 230V inverter. Both inverters run off the house bank.

The laundry machine is also wired directly to the Mastervolt Masterswitch to run directly off of shore power or the generator. I don't know if it will have problems with 60hz shore power.

There are 3 AC units that are wired to the Masterswitch. Again I don't know if they will have problems with 60hz shore power.

The watermaker and electric water heating element are also wired to the Masterswitch. And again, I'm not sure if either of those care about 60hz vs 50hz. I do imagine, however, that I probably won't need to run the watermaker when I'm at a marina, so that will probably only ever run off the generator.

The two Mastervolt battery chargers, I've been told, have no problems with 60Hz. Hopefully that is correct.

[Dsanduril]

With the caveat that the system is unseen and should have a bit of proper design....

To me, the simplest would be to swap out (or see if the current one can be used) the 4-wire ELCI for a 3-wire one (Blue Sea does make them). Then the neutral in the US shore power cord simply doesn’t get used/connected. Wire the two hot legs to get 240V into the iso xfmr. On the output side you’ll have 240V and the only difference from initial (Euro) configuration will be the frequency. The isolation transformer doesn’t really care that on one side you have two hot wires and on the other one that is nominally hot and one neutral. I think Jedi recently posted a couple of threads on typical installations pretty much along these lines.

That means the boat works pretty much as it always has and leaves you with the frequency question. The water heater won’t care, resistance elements don’t care about frequency. That leaves the AC, watermaker, and the washer. Those will have motors that will spin at 120% of rated speed. See this article for the considerations on switching motor frequency. Can you run them off the inverter rather than shore power (or at least washer and watermaker)? And just use shore power for battery chargers and water heating? That would be cleanest. If not then those devices would take very specific investigation.

For reference, our own boat is European, we run a battery charger and the water heater on shore power. Everything else gets run from inverter (includes a washer, watermaker is DC). We don’t have AC so that’s a major difference. For us that’s the easiest approach but there are many ways to attack this question. If the boat is going to be staying in 60Hz land for a long time it may be easier to fully convert. The downside to that is Euro boats are wired for 230v, most appliances in 60Hz-land are 120V and so require more current and the wires may be too small, so it’s a commitment to fully change. And you need to move to a 4-wire system if you have both 240V and 120V.

[Edit] and one other thought, it is unlikely the isolation transformer is sized for 50A, no reason you can’t supply it from a 50A circuit as long as you provide protection appropriate for the xfmr rating.

[Muaddib1116]

Thanks Dsanduril!

I'll try to check on how the Blue Sea box is wired.

As far as the frequency, I think if the laundry machine works well off the inverter, I'll just use that to run it, since I probably won't ever use the 230V inverter for anything else.

The watermaker, I will probably only ever use on the generator, because if I'm at a marina, there will probably be dock water.

That leaves the 3 AC units. Would they care about running at 60hz? That would mean the compressor motors would be running 20% faster?

In general, the less I have to change about the existing setup, the better, IMO.

I'm curious, if everything is wired correctly through the new Blue Sea box, and the boat is seeing 240V through 3 wires, if I'm every down in the Caribbean where they have Euro power, would I just need a plug adapter that feeds the ground and hot into the two hots of my American shore power cable?

[more]

I can't help you. I'm sorry to interrupt. For me is so funny

but I personally adore logical plug-and-play EU electricity grid. 230 / 380V 50Hz. Also if eletronic not plug and play i simply don't bay.
Almost in EU we left behind the imperial pipe size to DN "Diametre Nominal" per ISO from NPS "Nominal Pipe Size"

to an American engineer is so hard to work mean daily strange conversion after conversion. it is a TERRIBLE not logical system of measurement. i think is hard to find 1000 American who know (look video down)all imperial measurement name and also size because imperial measurement standard is all have SI units back for standard in the definition.
https://youtu.be/r7x-RGfd0Yk
And this was just for the distance measurements
for all measurement we need minimum 24 hour video

[smac999]

They should have run the 2 hot wires and ground to the transformer. There is nowhere to put the n. It does not even need to enter the boat. You will then have 240v 60hz in the boat.

The isotransformer will convert the ground wire from the North American reference point (halfway between the hots). To euro ref point grounded with one 230v line. So the transformer is required.

The transformer needs to be big enough to handle 50a. Otherwise they should have put a smaller breaker in.

Some of the on-board stuff may not like 60hz. Ie microwave, air con. Etc. You will need to read all the labels.

There is no easy way to convert the 60hz to 50hz. If the boat is staying here then start replacing gear with 60hz stuff.

You will also have no 120v outlets. They will be 240v

You could add a 120v subpanel from a step down transformer or auto transformer.

[sanibel sailor]

My system is very simple and never used now that I have solar, but I thought the isolation transformer should be first thing wired to the shorepower inlet, even before the "breaker enclosure" (although I am not sure what that is.)

[Dsanduril]

Originally Posted by Muaddib1116

....I'm curious, if everything is wired correctly through the new Blue Sea box, and the boat is seeing 240V through 3 wires, if I'm every down in the Caribbean where they have Euro power, would I just need a plug adapter that feeds the ground and hot into the two hots of my American shore power cable?

Yes, exactly. With the isolation transformer in place you don’t have any worries about two hots vs. hot/neutral on the shore power side. It gets more complicated if you can only find 120V at a US marina, but otherwise, sticking with 230/240 simplifies everything except frequency.

@more (with tongue very much in cheek) what SI units do you use for navigation at sea? Or does that basic mistake in the definition of the meter not bother you at all? I don’t think there’s anything particularly SI or even rational about the voltages selected for national grids. As for the rest, yes, sadly we have to make conversions every day. One day the rest of the world will stop making SAE bolts and imperial anchor chain and we’ll have to sort it out It will be nice when I don’t have to own two sets of tools.

[smac999]

Originally Posted by sanibel sailor

My system is very simple and never used now that I have solar, but I thought the isolation transformer should be first thing wired to the shorepower inlet, even before the "breaker enclosure" (although I am not sure what that is.)

No you need a main breaker before the isotransformer. And 1 after it as well. If the transformer is near the inlet it does not need to be an elci breaker.

[OS2Dude]

Originally Posted by Muaddib1116

The yard put a new Marinco 50A 125/250V inlet in, and wired it into a Blue Sea ELCI 50A 120/240V breaker enclosure in the lazarette.

Props for the ELCI breaker. (It is a mains breaker, cuts all but the safty ground?)

I would have them put in a SMARTPLUG inlet and cordset instead of the old fashioned style designed in 1938. Smartplugs are easier to use and safer too. In our case, I added an additional 120v circuit dedicated to our marine Air Conditioner. On both circuits I used SMARTPLUGs. I was considering changing to a 120/240 50A plug, but a boat electrician advised against it. (Likely because the boat had never been wired for it and the expense of updating the major components was quite high.)

[OS2Dude]

[QUOTE=OS2Dude;3412119]Props for the ELCI breaker. (It is a mains breaker, cuts all but the green safety ground?)

If you are bringing the boat to North America, keep the neutral and wire the boat accordingly. It will save you a lot of grief in the end.

The neutral wire splits the 240v wave into two 120v waves 180 degrees out of sync. In other words, the potential between the two HOT wires in a 240v circuit is, amazingly, 240v. If you tap the middle of the wave, the potential between each HOT wire and the NEUTRAL is now 120v, 180 degrees out of phase with the other.

If you do not REALLY understand what is being said in this thread, find a CERTIFIED MARINE ELECTRICIAN to explain it to you. Do not just take the word of a yard worker because that is what they've always done, or anyone else for that matter. Even a licenced land electrician likely doen not know the nuances involved in marine electrical circuits. [NO, I am not one, so 'Trust but Verify']