Electrical

[Dragonten]

My boat has a 120/240 input and a 240 only on each side. When I hook up to the 120/240 output of my marina am I only getting 120 ? If I hook up the 120/240 to the 240 would I get 240? An electrician friend told mine to me the 120/240 is three phase and the 240 single phase. Asking because my dryer and various other appliances require 240.Thanks,

 

[Pascal]

50 amp shore power whether 120/240 or 120 is always single phase. You ll only start getting three phase with some 100 amps shore power

120/240-50 which is pretty much standard on all boats under 70/75’ has two hots, a neutral and ground. It will give you 120v between each hot and the Neutral as well as 240v between both hots.

Note that on boats with isolation transformers, neutral is not connected to shore power but generated by the transformer.

 

[SKYCHENEY]

On a 1981 53MY you have a 120v 50amp inlet and a 240v 50amp inlet. The 120v is basically not used anymore. You will be using the 240 plug.

There is no 3 phase plug on your boat.

 

[Dragonten]

Thanks what I meant was according to my friend their will either be 3 phase 120/240 coming into the boat or in some marinas just 240 single phase. Does that matter? Sounds like from the responses regardless of my input voltage in either case I should be using my 240 volt input connection. Is this right? And should I be getting 240 volts inside the boat regardless of which input voltage I connect to?Thanks,

 

[Pascal]

You re not going to find 3 phase shorepower at slips smaller than 100’… especially in Illinois! Completely different animal. And 3 phase shore power isn’t 120/240 anyway but either 208 or 480 volts. Your friend doesn’t seem to know much about shore power

You will connect using the standard 120/240 volts 50 amps cord and pedestal which will power all your 120 volts and 240 volts needs.

 

[SKYCHENEY]

Your cord and inlet will be the same (240 inlet). But if the marina has a 208v 3 phase service, you will only be getting 208 volts to your 240v loads (anything on a double pole breaker). Normally, any single pole breaker would be fed 120v from a 208 service, but in your case since you have isolation transformers, you will be getting 104 volts to those circuits.

This IS an issue. You would be best served at these docks to be boosting that 208 to 240. This can be done with your current isolation transformers but you would need boost switches added to them if someone hasn't done that already.

 

[Boatsb]

It's common for 2 legs of 208 and a neutral to be on marina pedestals. It's cheaper.

3 phase is the commercial standard and transformers are needed to create correct 120/240 single phase. They're expensive.

This is why many yachts take in the the 2 legs with a transformer and creates the neutral with a phasing of 180 degrees. They up the voltage but have lower available amperage.

Remember nothing is free.

 

[Dragonten]

What will my voltage meter read in these different scenarios? Does it help me determine what is at the pedestal?Thanks,

 

[carolinacoast]

3 phase will be 4 prong, and your cord won't fit. as stated, that is for large yachts and looks different. Red or gray, not yellow and the marina will charge you $$ differently.
3 prong, 50 amp, and your voltage in the boat should be 220 or more at the panel. your transformers should take care of the rest.
Good luck. Your friend may not use a 50 amp 240v cord on his boat.

 

[Pascal]

I know some marinas use three phase to feed 120/240-50 like Sky described but personally I be never had to deal with that. Maybe a regional thing or older docks

Down here three phase is always 100amps and at larger slips over 90’.

Three phase 100 amps has 5 pins not 4… G N and three hots. You get 120 N to any H and 208 between any 2 H

Single phase 100 is the one with 4 pins G and 3 H, no neutral. Same with 480v three phase but the pins aren’t in the same location as the 4 pins single phase 100

Here is a 3 phase 208 outlet, left and single phase on the right. But these are completely different from what you ll find on any Hatts, except the few 90/100 footers they built

 

[cww]

In my area of the country (the South) 120v shore power is still pretty common at a lot of marinas, especially older ones and the ones that cater to smaller boats. Marinas that are close to the coast tend to have brand-new docks because they get wrecked by hurricanes every 10 years, and all of those seem to have 240v. But not so much once you get a little bit inland on a river, and once you get up into the areas of GA/NC/SC with older wooden docks. Sometimes we end up staying in one of those, and I like having the ability to use both, it's really a very nice feature that other boats don't have. Functionally they are not the same though, on the 240v side I can run almost everything on the boat, but when it's on 120v I have to leave 1 or 2 ac's off to avoid blowing the breaker.

I don't think either side is 3 phase though? That would be really unusual. Most marinas don't have 3 phase, and even in the ones that do it's usually only in the couple slips that accommodate 100+ footers, nothing close to our size has that. I think your friend is wrong on that point.

 

[Dragonten]

At the boat this weekend I plugged the power cord into the 240 labelled inlet on the boat. The voltmeter read 208 volts coming in.

 

[Captain Ralph]

At the boat this weekend I plugged the power cord into the 240 labelled inlet on the boat. The voltmeter read 208 volts coming in.

Newer dock, all good.

 

[Boatsb]

No. It's a problem.

Your gear is looking for 240 volts. 208 is 2 legs of a 208 3 phase and will run hotter. Boost transformer will fix this.

 

[Dragonten]

I was under the impression getting less than 240 was not good long-term for appliances that require 240. If I plug into the 120/240 inlet of the boat presume I get the same voltage 208? Reason I ask is that my voltmeter on that side may not be accurate so can't tell. Appeared to be reading 110 volts. So figure I should use the 240 inlet?

 

[Pascal]

120/240 is the same as 240. There is no difference between the 2. Both have two 120 hots, a neutral and a ground.

First thing is to get a meter and measure voltage at the pedestal. You should have 240 across the hots and 120 between each hot and neutral. Or close to that… under heavy loads (summertime, packed marinas) you will likely get. A bit less than 240. Right now the digital meters on my panel show 225 getting into the boat. That’s ok.

If you only have 208 between the hots then indeed your marina has inadequate shore power. And yes, 208 will cause some issues starting with the fact that you will not be able to get a full 50 amps causing breakers to trip even without a full load. Second many appliances will run hotter including compressors (Aircon and refrigeration)

After you check voltage at the pedestal, take reading at the panel. If you have the old analog needle meters, they may not be accurate so again use your multimeter and get a precise reading.

 

[Captain Ralph]

I was under the impression getting less than 240 was not good long-term for appliances that require 240. If I plug into the 120/240 inlet of the boat presume I get the same voltage 208? Reason I ask is that my voltmeter on that side may not be accurate so can't tell. Appeared to be reading 110 volts. So figure I should use the 240 inlet?

SOP is that 115 and 115VAC make 230Vac.
Unless, you are on a newer dock and there is a Wye or Star transformer supplying power to your dock from commercial service. Look around your dock, big box a buzzing?? That may be the transformer I am typing about.
Then, the 115Vac legs are then not perfectly in phase and the combined peak to peak signal is now 208Vac.
This 208Vac is still pushed by a very strong 50Amps.
With good current, all will run great.

Your adjustable SMX A C may alarm. Instructions are in the owners manual to re-call this.
Labels on your compressor tops state min Vac is 200.

Digital Volt Meters (DVM) measure ACv two different ways. Peek to Peek and RMS.
Simply, RMS will display a lil lower than P-P.
This is one of many reasons people say 110, 115 or 120Vac (220, 230, 240Vac). All mostly the same except 208.

 

[SKYCHENEY]

I was under the impression getting less than 240 was not good long-term for appliances that require 240. If I plug into the 120/240 inlet of the boat presume I get the same voltage 208? Reason I ask is that my voltmeter on that side may not be accurate so can't tell. Appeared to be reading 110 volts. So figure I should use the 240 inlet?

You are correct. Low voltage does cause heat and loss of efficiency in your compressors and electric motors. Its not ideal.

 

[Dragonten]

I wonder if this is the transformer at the dock being the refrenced?

 

[Sadey]

Just curious, what marina is that transformer at?