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Old 16-05-2011, 13:37   #1
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30 vs 50 Amps

I'm up-dating my electrical system and have the option of either going with 30 or 50 amps. Anybody have any thoughts? Any advantage to either?
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Old 16-05-2011, 13:44   #2
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Re: 30 vs 50 amps

It depends on the loads on your boat. 30a 120v will support 3.6KW of load. 50a 120v will support 6KW of load. 50a 120v connections are rarely found in US marinas. The more common "50a" connections are 50 a 120/240v, and they have a capacity of 12 KW.

You will either need to read the nameplate ratings of the equipment that you would be running simultaneously and add them up, or consult with a qualified electrician to determine what your boat needs.
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Old 16-05-2011, 13:46   #3
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Re: 30 vs 50 amps

How big is your boat? Do you need 50 amps? What would be drawing that much, multiple large airconditioners? My boat is 38 ft with 30 amp service, it's true that if my wife uses the blow dryer for her hair, I have to turn off the hot water heater to keep from blowing a breaker but that's about the only time a few more amps would be needed.

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Old 16-05-2011, 14:03   #4
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Re: 30 vs 50 amps

This site is awesome. I posted my question 10 minutes ago and am getting advice already. If I could take you guys for a beer ( or three!) I would.

My boat is 33' and while I may run AC in the future I'm primarily concerned with the basics, if a computer, hot plate, shore-side frig and hot water and the occasional power tools .
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Old 16-05-2011, 15:44   #5
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Re: 30 vs 50 amps

30 amps is usually sufficient for a 33 footer if properly wired and distributed.

I would, however, give you a cheaper option: Install a second 30 amp circuit and then wire that to a beefed up circuit breaker/fuse setup. You will find two 30 amp cords cheaper and easier to handle than a 50 amp, and it means you only run the second 30 amp circuit when you require it.

That's what I have on my 41 footer...except I've not yet needed both 30 amp inputs. Were I to charge my expanded battery bank and run my A/C at the same time, I would need it.
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Old 16-05-2011, 15:56   #6
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Re: 30 vs 50 amps

Quote:
Originally Posted by JohnnieBsailing View Post
This site is awesome. I posted my question 10 minutes ago and am getting advice already. If I could take you guys for a beer ( or three!) I would.

My boat is 33' and while I may run AC in the future I'm primarily concerned with the basics, if a computer, hot plate, shore-side frig and hot water and the occasional power tools .
All of which would necessitate 50 amp service if you intend to run any of them simultaneously, i.e., AC, hot plate, hot water heater. It isn't the size boat but the size load(s) that should be your consideration.
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Old 16-05-2011, 16:05   #7
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Re: 30 vs 50 amps

One thing to consider is that some marinas charge extra for 50 amp service. I have 30 amp cord on my 37 foot cat and, because of the extra charge for a 30 amp service, use a converter to step down to a 15 amp plug. I monitor the current when using some of the larger appliances and shift the load around to suit. Saves me 30 bucks a month. I run an AC during the summer. Turn it off while using the Mr coffee. Works for me.
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Old 16-05-2011, 17:19   #8
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Re: 30 vs 50 amps

You can run 30 on your 50 system and it runs superb.
All ya need are plug adapters.

Ya can't run 50 on your 30.
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Old 17-05-2011, 23:48   #9
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Re: 30 vs 50 amps

I have a 50 amp wired boat and I use an adaptor with two 30amp plugs. Most marina electrical boxes are wired with each 30 amp receptacle on a separate "leg." The means that by using two 30 amp plugs I can get the 240VAC that my boat uses for some equipment.
- - But in most cases 30 amp is all you ever need and if you are going to go heavy into air cond. then the separate 30 amp connector/wiring is the way to go.
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Old 18-05-2011, 05:03   #10
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Re: 30 vs 50 amps

I get confused with people referring to 30Amp/50Amp
Surely you all mean American 110Volts versus 208/230Volts?
If this is the case, and you intend to remain in America then 110 is the way to go....
No compromise with purchasing stuff!
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Old 18-05-2011, 05:43   #11
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Re: 30 vs 50 amps

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Originally Posted by AllezCat View Post
I get confused with people referring to 30Amp/50Amp
Surely you all mean American 110Volts versus 208/230Volts?
Yikes...

If you don't understand the difference between amperage and voltage, perhaps you need to basic electrical training.
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Old 18-05-2011, 05:53   #12
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Re: 30 vs 50 amps

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Originally Posted by AllezCat View Post
I get confused with people referring to 30Amp/50Amp ...
In North America, standard Shore Power service is available as:
- 30 Amp 125 Volt 3w
- 50 Amp 125 Volt 3w
In both the above 30 and 50-ampere systems, the shore power cord contains three conductors.
Black is ungrounded (“hot”) and carries 125 volts of electricity, white is grounded conductor or neutral, and green is the grounding conductor.
- 50 amp 125/250 volt 4w
- 00 Amp 125/250 Volt 4w
The 125/250v shore power cords contain four conductors – the white neutral conductor, the green grounding conductor, and red & black ungrounded conductors each carrying 125 volts.

See theexcellent
Marinco Guide to AC Electrical ➥
http://www.marinco.com/files/media/g...r%27sGuide.pdf
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Old 18-05-2011, 06:28   #13
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Re: 30 vs 50 amps

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Originally Posted by doug86 View Post
Yikes...

If you don't understand the difference between amperage and voltage, perhaps you need to basic electrical training.
I understand electricity perfectly.
I understand American shore power systems perfectly.
I understand the difference between American and Australian systems.(I assume European systems are same as Australian)
I don't understand people referring to 30/50amp
When they really need to know whether they need 110 or 220(208 where I am now)

Surely the question is voltage.
I am thinking, maybe incorrectly, the op is deciding to go for 220v or 110v.
And my advise remains.
Referring to 30amp or 50amp shore power is a misnomer.
The 30amp is usually 110 and the 50amp is usually 220 and that is what your hair dryer cares about...
the gauge of wire is the same as for DC - bigger for more amps...
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Old 18-05-2011, 06:47   #14
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Re: 30 vs 50 Amps

In North America, the consumer gets two hot wires (180 deg out of phase with each other) and one neutral wire. Neutral to either hot gives us 120 V single phase. Hot to hot gives us 240 V single phase. (This 240 V is, AFAIK, not compatible with Euro or Aussie gear, which- IIRC- uses a hot 220 and a neutral.)

The standard shorepower connection around here carries up to 30 A of 120 V single phase. This gives you a ground, a neutral and one of the two hot wires. A standard North American wall outlet is 15 A, 120 V single phase (ground, neutral, one hot).

If you pay extra for onboard wiring, cables and marina fees, you can get a larger plug that is wired identically, but carries 50 A of 120 V single phase. I believe this is what our OP is referring to. And I would argue that, if the boat's onboard gear is capable of drawing this much current, you should wire for 50 A on the boat side of the cable. You can always connect a boat wired for 50 A 120 V to a bollard providing 30 A 120 V, if that's all that's available.

The other connections GordMay mentioned are 120/240 V. This gives you a ground, neutral and both hot wires, just like the main supply coming into a house. North American 240 V equipment (high power air conditioners, etc) can then be run from the same connection as 120 V computers and coffee makers. This connection is not compatible with any of the 3-wire 120 V options.
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Old 18-05-2011, 06:49   #15
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Re: 30 vs 50 amps

Quote:
Originally Posted by AllezCat View Post
I understand electricity perfectly.
I understand American shore power systems perfectly...
... Referring to 30amp or 50amp shore power is a misnomer.
The 30amp is usually 110 and the 50amp is usually 220 and that is what your hair dryer cares about...
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.
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