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Old 29-11-2014, 16:03   #31
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Re: 240v Shore Power Connection

Some people here are giving very dangerous advice. Some of the rest don't know what they are talking about. One guy said he changed out all 240vac accessories to US 120vac ones. This runs the risk of overloading the wiring and causing fires that fuses and breakers might not prevent. Typically 240vac installations use smaller gage wiring because the amperage is half that carried on a 120vac circuit. Of course he could have stripped out all the wiring as well and replace with larger a larger gage.


Are you sure the USVI is a 220-224vac 4-wire system? I would have thought the USVI was the same as the US. Standard US is 120vac 60Hz single phase (not 3-phase as someone said). In the US we just sent two 120vac wires to the water heater, dry and oven and call it 220-240. You can order 3-phase but it costs extra and requires an extra transformer tap and usually an onsite transformer which you have to buy.


3-Wire boat to 4-Wire dock power at the same voltage is an interesting problem. Whomever said you need expert advices was right on. I've used a thing called a "Smart Y" (West Marine) on a 240vac, 4-wire boat to hook to a two 120vac dock outlets but it only allowed us to power one AC bus, not both. Works ok, got some cold air and hot water. Maybe there is some kind of "Smart" something out there that will work for you.


Some people here are giving very dangerous advice. Some of the rest don't know what they are talking about. One guy said he changed out all 240vac accessories to US 120vac ones. This wouldn't help in this case anyway. This runs the risk of overloading the wiring and causing fires that fuses and breakers might not prevent. Typically 240vac installations use smaller gage wiring because the amperage is half that carried on a 120vac circuit. Of course he could have stripped out all the wiring as well and replace it with larger a gage.


Some guys say transformers. There also is probably one out there that will work in your case. The one's we needed were expensive, big, heavy, noisy and generate lots of heat so we went with Smart Y.

Yes, low frequency polar can damage certain motors which create a reactive low. Frequency is usually a function of the gen-set unless you have a super-fancy constant speed drive like on airplanes new mega-yachts. Usually 1500rpm for 50Hz and 1800rpm for 60Hz. Most charter operators like 50Hz for less noise and fuel burn.



Reverse polarity will not only damage some components but it can be deadly. Our charter operator in Raiatea solved the RP problem with his dock power by cutting the wire to the RP warning light on our electrical panel. We discovered it on the next trip. I wondered by most of his dock outlets were smoking ruins.


An Isolation transformer on the dock power ground is a very good idea any time.

Capt. Jack


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Old 29-11-2014, 17:50   #32
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Re: 240v Shore Power Connection

Capt Jack...the only way I could get 240v power out of the power pole wes to connect my 2 "hot" wires to the respective "hots" on the pole. And then I connected my 3rd wire to the ground point on the plug....no neutral used! It worked...I had 240vAC at the boat, and my onboard equipment all seemed to work normally. BUT...my revere polarity light was on. I switched the 2 "hot" leads, but it made no difference. I used it that way for a day....but I donot believe that is the way it should be! Until we get this sorted out, we're on internal genset power! If an isolation transformer is what's required, then I'll need to find one. But if there is a different way, I'd like very much to go that way.
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Old 29-11-2014, 18:02   #33
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Re: 240v Shore Power Connection

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Originally Posted by jmschmidt View Post
Some people here are giving very dangerous advice. Some of the rest don't know what they are talking about. One guy said he changed out all 240vac accessories to US 120vac ones. This runs the risk of overloading the wiring and causing fires that fuses and breakers might not prevent. Typically 240vac installations use smaller gage wiring because the amperage is half that carried on a 120vac circuit. Of course he could have stripped out all the wiring as well and replace with larger a larger gage.
Yep, some people haven't a clue about the topic.

A circuit breaker protects the wiring by not allowing more current that the wire can handle, regardless of the voltage. Hence you can use the same wiring and same breakers you used for 240v in the EU for 120v US power. No overload, no fire as the breaker is watching current flow, not voltage. If the 240vac circuit is protected at 10a, it will carry 10a at 120v without a problem.
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Old 29-11-2014, 18:42   #34
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Re: 240v Shore Power Connection

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Originally Posted by DotDun View Post

A circuit breaker protects the wiring by not allowing more current that the wire can handle, regardless of the voltage. Hence you can use the same wiring and same breakers you used for 240v in the EU for 120v US power. No overload, no fire as the breaker is watching current flow, not voltage. If the 240vac circuit is protected at 10a, it will carry 10a at 120v without a problem.
Only problem with this theory is that the European equivalent of North America's 30 amp shorepower is 16 amps @ 240 volts. Individual circuits in North America are most often 15 amps @ 120 volts. In Europe individual circuits are usually about 8 amps A 240 volts.

If the circuits are protected by the proper size breakers in Europe they will certainly not handle the current of a comparable circuit in North America.

At half the voltage the amperage doubles.
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Old 29-11-2014, 19:09   #35
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Re: 240v Shore Power Connection

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Originally Posted by mitiempo View Post
Only problem with this theory is that the European equivalent of North America's 30 amp shorepower is 16 amps @ 240 volts. Individual circuits in North America are most often 15 amps @ 120 volts. In Europe individual circuits are usually about 8 amps A 240 volts.

If the circuits are protected by the proper size breakers in Europe they will certainly not handle the current of a comparable circuit in North America.

At half the voltage the amperage doubles.
Nobody is suggesting to change the breakers!

Again, with the same circuit breaker, the amperage can't double, the breaker will trip! A breaker trips on current not voltage, it doesn't care about voltage.

What you are struggling to understand is connecting a EU wired boat to US electric with only yield half the power, but it will not hurt the wiring!! The power is half due to the voltage is halved.

Using your example, a EU boat with 8a branch circuit will still deliver 8a at 120v. Please explain how this is dangerous? You will only get 960w from this circuit vs. 1920w, but it's not dangerous!!
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Old 29-11-2014, 19:18   #36
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Re: 240v Shore Power Connection

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Originally Posted by DotDun View Post
Nobody is suggesting to change the breakers!

Again, with the same circuit breaker, the amperage can't double, the breaker will trip! A breaker trips on current not voltage, it doesn't care about voltage.

What you are struggling to understand is connecting a EU wired boat to US electric with only yield half the power, but it will not hurt the wiring!! The power is half due to the voltage is halved.

Using your example, a EU boat with 8a branch circuit will still deliver 8a at 120v. Please explain how this is dangerous? You will only get 960w from this circuit vs. 1920w, but it's not dangerous!!
That is not an effective solution really. A North American boat can use a 1500 watt water heater, kettle, toaster, etc, all @ 120 volts - all within the 15 amp rating of a typical circuit. By keeping the same breakers and possibly wiring too small all the owner of the European boat has to do is find appliances that use half the current. Good luck finding 800 watt water heaters, toasters, kettles, etc.
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Old 29-11-2014, 19:39   #37
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Re: 240v Shore Power Connection

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Originally Posted by mitiempo View Post
That is not an effective solution really. A North American boat can use a 1500 watt water heater, kettle, toaster, etc, all @ 120 volts - all within the 15 amp rating of a typical circuit. By keeping the same breakers and possibly wiring too small all the owner of the European boat has to do is find appliances that use half the current. Good luck finding 800 watt water heaters, toasters, kettles, etc.
1) We're not discussing a "North American boat"

2) EU wiring is not 'too small', it's protected with the properly sized circuit breaker (10A and 16A, I've not seen 8A).

3) A 1500w EU water heater (6.25A @ 240V) will be a 375w water heater on 120v. (If you understand ohms law, you will understand this) Yes, the EU appliances that heat will take longer, but will work. Those with electronics, all bets are off, read the label!

4) Both my 120v toaster and coffee maker are 800w or less. My water heater is 750w rated @120v - I've run it on 240v with no problem.
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Old 30-11-2014, 07:54   #38
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Re: 240v Shore Power Connection

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Our boat(of 16 years) was built and used in Asia and the Med--until now. She is wired for 240v AC power,with a 3 wire sysyem-hot, neutral, and ground. We just arrived in the USVI, and plan to spend the next several years here in the Caribb. Unfortunately, the 240v(220-240v) available is based on a 4-wire system; 2 hots, neutral, and ground. Is there a way I can connect my 3-wire AC system to the 4-wire system we've found on marina power poles? We tried putting 2 wires to the "hot" and the third to gnd....we got 240vAC on the boat, but is shows reverse polarity, and switching the 2 "hot" wires did no correct the reverse polarity. Help!!!
"We tried putting 2 wires to the "hot" and the third to gnd....we got 240vAC on the boat, but is shows reverse polarity, and switching the 2 "hot" wires did no correct the reverse polarity."

Stop right now! Hire a qualified marine electrician. You are messing with dangerous stuff. 240 volt electricity is not something to experiment with..

You've been give some good advice but more bad advice and now posters are just arguing among themselves. How can you tell the difference?

Hiring a qualified marine electrician (not some hack hanging around the marina) will be less expensive in the long run than burning down your boat or paying for a funeral. Think about it. And don't experiment any more.
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Old 30-11-2014, 17:37   #39
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Re: 240v Shore Power Connection

I'm the guy that removed the 240v from my boat. I did replace the panel and I did remove everything associated with the 240v. I have not yet added shore power since I currently do not need it. When I do, of course the wiring to whatever AC I need will be new and up to code.

I was giving an example of how I dealt with the same problem. In my case I was never going to go back to 240v. And yes, absolutely hire a qualified electrician. In my case I traced all the DC wiring and labeled it for the electrician to wire up the panel. When it's time for AC I'll hire one again.
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Old 30-11-2014, 19:48   #40
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Re: 240v Shore Power Connection

if I was a marina manager and an out of county boat showed up and was trying to rewire his plug / boat at the side of the dock I'd be taking an axe to his lines as fast as I could.


some of you people are ridiculous and are a danger to yourself and others. as kids did you go around sticking forks in outlets too? do you still do it as adults?
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Old 30-11-2014, 19:50   #41
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Re: 240v Shore Power Connection

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if I was a marina manager and an out of county boat showed up and was trying to rewire his plug / boat at the side of the dock I'd be taking an axe to his lines as fast as I could.


some of you people are ridiculous and are a danger to yourself and others. as kids did you go around sticking forks in outlets too? do you still do it as adults?
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Old 30-11-2014, 20:25   #42
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Re: 240v Shore Power Connection

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if I was a marina manager and an out of county boat showed up and was trying to rewire his plug / boat at the side of the dock I'd be taking an axe to his lines as fast as I could.....
Most marinas I know usually insist on their own guy replacing the pedestal plug to their type and are very helpful in helping the boater confirm the voltage on their Boat's deck plug side but take no responsibility that it is suitable for the consumers.

As rwidman correctly said in my other thread.... they would never let you hardwire into their pedestal.

So your comment seems a bit reactionary...... given that plugs/power supplies can differ even within the same country and breakers are used on either end.
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Old 02-12-2014, 13:05   #43
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Re: 240v Shore Power Connection

With over that 15,000 hrs. of flying time in 40 different types of airplanes I've seen breakers fail to open and smoke and fire result. If an originally designed 240vac circuit is fused at typical EU amperages, say 10a, you are correct that a properly functioning breaker will open when a down-line device demands more, say 20a, but that just means that device will not operate. I guess that's one way to really find out how much your bilge pump draws and if you should upgrade the wire size, but do this at the dock please. Capt. Jack
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Old 03-12-2014, 05:24   #44
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Re: 240v Shore Power Connection

Gentlemen: the discussions have been very interesting and informative, and I do thank you all for your comments and contributions.....but the question at hand remains--how to connect a 240vAV, 3-wire (hot/240v-neutral-ground) boat to a US-wired marina power pole that offers 110vAC(3-wire) or 240vAC 4-wire (hot/110-hot/110-neutral-ground). I've heard "Isolation Transformer" mentioned a few times, and doing some digging on it-it seems that may be one possible fix. The "Smart Y" is another mention, but it requires 2-110v power pole ports and gives (I think)240v 4-wire output...no good for this application..(unless I misread the literature on the output). But are there any other ways to make them compatible.... save rewiring the whole boat for 110v and replacing all the installed AC equipment...also not an option as the boat will see both 240vAC 3-wire service and 110v AC service in the future?
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Old 03-12-2014, 08:26   #45
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Re: 240v Shore Power Connection

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Gentlemen: the discussions have been very interesting and informative, and I do thank you all for your comments and contributions.....but the question at hand remains--how to connect a 240vAV, 3-wire (hot/240v-neutral-ground) boat to a US-wired marina power pole....
You have also posted this question on two Cruising Association forums that I have responded too and yet you still say you don't have the answer?

One very clear message here has been not to play with and re-wire plugs yourself. Here is my response to your question on the CA Forum.

Whatever you do don't take advice to take the two hot wires and connect them to the live and neutral on your boat. This will cause reverse polarity lights to come on and means that the normally safe Neutral bus bars which would normally be at around zero volts are now at 120v. Yes this will give you 240v but if there are other faults on the boat then this could be a disaster. My neutral bus bars on an American built boat are exposed in a large area above the engine where tools and other AC and DC cables and bus bars are routed. Playing about with AC could kill you or someone swimming in the water around your boat. There are plenty of documented accidents about "messing about with AC". Water and AC don't mix well.

There are two answers, the first and simplest is to have an isolation transformer fitted by a qualified Marine Electrical engineer who really knows his stuff to step the voltage up from 120 to 240v, the second is to have a US shorepower socket fitted with the 120v split phase feeds wired to dedicated extra 240 sockets that just run from the new 4 pin shorepower fitting. Any permanently wired-in AC loads like an immersion heater would have to be re-cabled with a standard 13amp plug and plugged into the new US 240v sockets when in the US or into the UK 240 v sockets when in the UK.

The other important consideration is to make sure your shorepower charger will work on ANY input voltage and frequency, or buy a second maybe smaller charger that can be used to charge the batteries anywhere. This can supply power whilst your 50 Hz inverter is running to supply your 240 volts AC at the correct Hz for frequency dependent equipment like washing machines or Air-Con. It is better to have 240 volt 60 Hz kit that will work well in 50 Hz countries, it will also run slower in the UK but will work fine - just not as efficiently.
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