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Old 18-05-2011, 09:49   #31
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Re: 30 vs 50 Amps

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Originally Posted by St. Elsewhere View Post
North American single phase appliances are almost all designed for 120 or 240 volts. 110 and 220 volt rated appliances are not found here. Wiring devices (outlets, plugs, wire, etc) may show ratings above such voltages that they are intended to supply.

The correct RMS AC voltage may be 120VAC but for whatever reason I have seen US appliances that specified 110, 115, 120 or 125 V or some combination or range in those limits.
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Old 18-05-2011, 10:29   #32
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Re: 30 vs 50 Amps

I'm going to go way back to the original question.

-- I'm assuming that you won't have any 240v equipment on the boat

-- and the air conditioning will be not more than about 20,000 BTU

The only time you'll really need the 50amp service is with the air conditioning as air conditioning compressors briefly draw high amperage on startup that can easily pop 30amp dock breakers.

My first choice is to install a 50amp 120v outlet on the boat (with appropriate breakers etc inside). I'd then buy a 50ft 30amp cord and 50ft 50amp 120v cord with adapters such that you could plug into 50amp/240v or 30amp 120v at the marina. You can also connect the two cords together to get 100ft of 30amp in case the power pedestal is way in the wrong place. This is very simple wiring in the boat but does cost a little more in cords and adapters. You end up with a lot of flexibility for your money. Most of the time you don't need air conditioning so you would just use the 30 amp cord (and pay for 30amp from the marina).

The alternative would be two 30amp boat outlets but this would still put the air conditioning on one 30amp outlet. You have to be sure that the air conditioner starting load would not exceed this number. It's also more complicated to wire safely inside the boat. My bet is that it would cost more in the end than the single 50amp outlet.

I have a version of the first solution and it has served me well.

Carl
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Old 18-05-2011, 10:39   #33
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Re: 30 vs 50 Amps

Some great info here. Let's add another question...What do North American cruisers do when they hit European marinas? And wouldn't places like St. Martin/ St. Marteen be on a European system?
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Old 18-05-2011, 10:53   #34
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Re: 30 vs 50 amps

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Originally Posted by GordMay View Post
It doesn't appear, to me, that you do understand "perfectly".
ie: 50 Amp (1 phase) can (equally) be either 120 Volt 2 Pole 3 Wire or 120/240 Volt 3 Pole 4 Wire (125/250V).
See the Marinco guide.
What Gord said. You seem to be a little confused.

50 amp or 30 amp refers to the amount of power which can be delivered through your shore power connection at whatever voltage it is -- in this case, 120 volts. 50 amp and 30 amp are typical ratings for 120v shorepower connections. A 50 amp connection will give you approximately 6kW of power -- enough for some air conditioning systems. A 30 amp connection will give you about 3.6kW of power, which is not usually enough for boats with air conditioning. All of these connections are at 120 volts.

It is very common in the US for boats that need more than 30 amps of power to have TWO 30 amp shore power connections.

In Europe, the typical shore power connections are either 16 amps or 32 amps at 230 volts, which give 3.6kW (approximately) and 7.3kW of power respectively. Again -- 16 amps at 230 volts is enough unless you have a big boat or you have air conditioning; otherwise you will need a 32 amp connection.
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Old 18-05-2011, 10:58   #35
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Re: 30 vs 50 Amps

Two challenges for Americans using European power - voltage and frequency.

Voltage is easy. You need a transformer. This can be as simple as a $100 box that sits on the dock or as fancy as a permanently installed isolation transformer (see Victron Energy for an example of the latter).

Frequency is hard. There's no economical way to convert European 50hz to US 60hz. Many things on the boat don't care about frequency but electric motors do -especially air conditioning motors. You have to look at each piece of equipment on your boat to see if it can handle 50hz. You can run 50hz on the boat wiring just don't turn on anything that minds.

My solution has been to have an extra large battery charger that accepts a wide range of voltage and frequency. When inside the US, I have a spare charger. When outside the US, the power cord only goes to this charger and is isolated from the other AC circuits. I then use the inverter to provide 120v 60hz to the boat. This works fine but is limited to the capacity of the charger and inverter so I can't run much air conditioning.

Carl
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Old 18-05-2011, 13:35   #36
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Re: 30 vs 50 amps

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Originally Posted by Dockhead View Post
What Gord said. You seem to be a little confused.

50 amp or 30 amp refers to the amount of power which can be delivered through your shore power connection at whatever voltage it is -- in this case, 120 volts. 50 amp and 30 amp are typical ratings for 120v shorepower connections. A 50 amp connection will give you approximately 6kW of power -- enough for some air conditioning systems. A 30 amp connection will give you about 3.6kW of power, which is not usually enough for boats with air conditioning. All of these connections are at 120 volts.

It is very common in the US for boats that need more than 30 amps of power to have TWO 30 amp shore power connections.

In Europe, the typical shore power connections are either 16 amps or 32 amps at 230 volts, which give 3.6kW (approximately) and 7.3kW of power respectively. Again -- 16 amps at 230 volts is enough unless you have a big boat or you have air conditioning; otherwise you will need a 32 amp connection.
I do understand it perfectly - not confused at all.
While all you wrote maybe true.
To get 220v in USA the 50amp connection gives it.(but it also gives 110v like the 30amp)
this is the issue that I continually point out.
So when someone refers to "50amp" there is a major difference as to whether they desire 220volts or 110volts.
I'm plugged into "50amp" now and getting 208v. The 50Amp is meaningless -20amp capacity would be plenty.
Supplying 110v to my boat -no matter the amperage capacity of the breakers and lines - would be very problematic.
I think this is the issue that many neglect casing the confusion...
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Old 18-05-2011, 13:41   #37
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Re: 30 vs 50 amps

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I think this is the issue that many neglect casing the confusion...
The only one causing any confusion is you. There is no 220V 50amp dockside service, it's either 120volts or 240 volts in the US.
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Old 18-05-2011, 13:59   #38
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Re: 30 vs 50 Amps

Allez Cat said "I'm plugged into "50amp" now and getting 208v."

Unfortunately many of our "240 volt" docks use the 208/120 "Y" connected three phase systems because they are cheaper. To get the proper 240 at such docks you need to have a dual tap isolation transformer installed.
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Old 18-05-2011, 14:04   #39
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Re: 30 vs 50 amps

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The only one causing any confusion is you. There is no 220V 50amp dockside service, it's either 120volts or 240 volts in the US.
Don't they call it "50amp"?
When I arrived in the USA the guy said
"you want 30amp or 50amp?"
"I need 220volts mate"
"we only have 30amp or 50amp"...
I now know the correct answer to the question is "50amp"
then I go with my meter and check that it is giving me 208/220...
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Old 18-05-2011, 14:07   #40
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Re: 30 vs 50 Amps

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Originally Posted by St. Elsewhere View Post
Allez Cat said "I'm plugged into "50amp" now and getting 208v."

Unfortunately many of our "240 volt" docks use the 208/120 "Y" connected three phase systems because they are cheaper. To get the proper 240 at such docks you need to have a dual tap isolation transformer installed.
208Volts is common in New York City
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Old 18-05-2011, 14:14   #41
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Re: 30 vs 50 Amps

For what it's worth....and I'm NO electrician, our 30 amp service is usually good enough for our needs BUT we are traveling now and often (in Marinas outside US) find that Marina's do not have (or do not have many) 30amp service connections. We have had to buy an adaptor so we can plug our 30 amp into the 50 amp connection at the dock.
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