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Old 16-01-2017, 17:02   #1
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Shorepower Voltage/Amp Difference Question

This is probably simple, and I think I used to know the answer, but I've forgotten if I ever did -

With shorepower terminals that offer 30/50 amp and 120/240 voltage with 3 or 4 prongs,

How do the differences work themslves out exactly and what does it mean for a shorepower cord that is rated 120/240 volts differ exactly from one only rated for 120 volts? How is it possible one is rated for either/or or how does this work itself out?

Thanks!

Kevin
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Old 16-01-2017, 17:34   #2
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Re: Shorepower Voltage/Amp Difference Question

The difference is in the number of wires and the type of plugs (plus the wire gauge for the different max Amps).

https://www.cablewholesale.com/suppo...ower_cords.php
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Old 16-01-2017, 17:57   #3
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Re: Shorepower Voltage/Amp Difference Question

30A cord is 120VAC - 3 pins hot, neutral, ground.

50A cord is either 120V (not so common) with 3 pins same wiring but heavier conductor and different plug layout.
50A cord can also (more commonly) be 120/240V with 4 conductors arranged as 3 pins (hot-a, hot-b, neutral) plus ground supplied by the metal ring around the plug.

None are interchangeable without some form of adaptor or pigtail.
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Old 16-01-2017, 20:13   #4
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Re: Shorepower Voltage/Amp Difference Question

Remember that the wire is sized for the amps, not the volts, so a 120v 50amp cable could handle 240 (or 480) as well.

Most US Marinas have 50a 125/250v four wire circuits:

Green = Ground
Black = Line 1
Red = Line 2
White = Neutral (Grounded)
All voltages are max ratings, actual will be 117 and 238 or so

125 volts Black to White
125 volts Red to White
250 volts Red to Black

the Green (grounding) wire will be connected to the White (grounded) wire at the shoreside transformer but NOT on the boat.

In Europe you'll see 16 and 32 amp three wire systems carrying 230 amps... but that's another post!
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Old 16-01-2017, 21:11   #5
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Re: Shorepower Voltage/Amp Difference Question

Everything you ever wanted to know:

Marinco 2017 Catalog

See, especially, pp 8-37.

Bill
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Old 16-01-2017, 22:43   #6
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Re: Shorepower Voltage/Amp Difference Question

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Originally Posted by Scott Berg View Post

In Europe you'll see 16 and 32 amp three wire systems carrying 230 amps... but that's another post!
I assume you meant 230V not 230 amps.

For the 4 prong 50amp 120/240v plugs, depending on what prongs are connected you can output:
- 50amps at 240V for a total or
- 50amps per leg for a total of 100amps at 120v. (though you can't use a 60amp device as the two 50amp legs are out of sync but not many 60amp-120v devices are available)
- In either case, you max out around 12000watts.

By comparison the typical 30amp 120v plug puts out a max of around 3600watts or a little more than 1/4 as much power.

PS: of course these are all nominal ratings. Reality before popping a circuit breaker will vary and if you dig into the specs they aren't really even rated for these amounts on a continuous basis.
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Old 17-01-2017, 08:29   #7
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Re: Shorepower Voltage/Amp Difference Question

[QUOTE=valhalla360;2305209]I assume you meant 230V not 230 amps.

OOOOPS!
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Old 17-01-2017, 08:41   #8
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Re: Shorepower Voltage/Amp Difference Question

Here is a good analogy:
Think of electricity like water and your shore cord as a hose.
Your boat needs 25 amps (or let’s say gph just for fun)
If you have a hose that will deliver 25 gph it is at its limit.
If you have a hose that can deliver 50 gph then 25 is no problem.
If you try and push 50 gph through your 25 gph hose, you will most likely burst the hose.

Now Voltage is Electromotive force,,, think of it as the pressure pushing the water through the hose.
If your boat requires 240 volts of force, and you try pushing them with only 125 volts of force, they probably wont work at all. If you try pushing your 120 volt equipment with 240 volts of force, your going to blow up all your gear.

That is it in a nutshell.

Hope this helps.

M
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Old 17-01-2017, 10:29   #9
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Re: Shorepower Voltage/Amp Difference Question

Just remember that wire is sized for a maximum amp load. If you switch from a 120 v connection to a 240 connection at the same wattage you will be cutting the amp load on your wires in half. It really is that simple.
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Old 17-01-2017, 18:35   #10
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Re: Shorepower Voltage/Amp Difference Question

Quote:
Originally Posted by captmikem View Post
Here is a good analogy:
Think of electricity like water and your shore cord as a hose.
Your boat needs 25 amps (or let’s say gph just for fun)
If you have a hose that will deliver 25 gph it is at its limit.
If you have a hose that can deliver 50 gph then 25 is no problem.
If you try and push 50 gph through your 25 gph hose, you will most likely burst the hose.

Now Voltage is Electromotive force,,, think of it as the pressure pushing the water through the hose.
If your boat requires 240 volts of force, and you try pushing them with only 125 volts of force, they probably wont work at all. If you try pushing your 120 volt equipment with 240 volts of force, your going to blow up all your gear.

That is it in a nutshell.

Hope this helps.

M
Well said, captmikem. I've always loved the water analogy for electrical/electronic explanations. When I was studying for my bsee and msee, the professors at Purdue and USC used it over and over for teaching. Only in the more esoteric forms of electronics does it (sometimes) not work well.
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Old 17-01-2017, 18:36   #11
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Re: Shorepower Voltage/Amp Difference Question

"
the Green (grounding) wire will be connected to the White (grounded) wire at the shoreside transformer but NOT on the boat."

In Europe, many electricians advised me to give up any grounding line on board.

I cut off the third line (yellow /green) on sockets, thus avoiding contacts, or latent currents, which made the breakers intervene (OFF) all the time , under shore power.

Under generator, there is no third line...thus i feel OK, as it is, 95% of. my power source
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Old 18-01-2017, 03:10   #12
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Re: Shorepower Voltage/Amp Difference Question

It's very dangerous to cut the green wire as you can have an energized equipment case and not know it until it's to late.

The only safe way to interrupt the green wire in a shore cord is the installation of a galvanic isolator or isolation transformer. Anything else is gambling lives.
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Old 18-01-2017, 06:17   #13
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Re: Shorepower Voltage/Amp Difference Question

Quote:
Originally Posted by Scott Berg View Post
Remember that the wire is sized for the amps, not the volts, so a 120v 50amp cable could handle 240 (or 480) as well.

Most US Marinas have 50a 125/250v four wire circuits:

Green = Ground
Black = Line 1
Red = Line 2
White = Neutral (Grounded)
All voltages are max ratings, actual will be 117 and 238 or so

125 volts Black to White
125 volts Red to White
250 volts Red to Black

the Green (grounding) wire will be connected to the White (grounded) wire at the shoreside transformer but NOT on the boat.
Most US marinas will also have 30 amp circuits.

Some will have only 30 amp circuits. Some will have only 50 amp circuits. If you plan to cruise, you should carry adapters so you can plug your boat into either.
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Old 18-01-2017, 06:20   #14
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Re: Shorepower Voltage/Amp Difference Question

Quote:
Originally Posted by TheThunderbird View Post
.................... In Europe, many electricians advised me to give up any grounding line on board.

I cut off the third line (yellow /green) on sockets, thus avoiding contacts, or latent currents, which made the breakers intervene (OFF) all the time , under shore power.

Under generator, there is no third line...thus i feel OK, as it is, 95% of. my power source
1) "Real" electricians or just guys that worked on boats?

2) There is a reason for all the wires, none are optional. If you cut the ground wire off, you are endangering yourself, your passengers or crew, and anyone who happens to touch and grounded metal on your boat.

Reconnect the ground wires and correct whatever fault was causing a problem.
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Old 18-01-2017, 15:04   #15
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Re: Shorepower Voltage/Amp Difference Question

There were professionals.

I have 3breakers upfront on board, a 4th one on the piwrr box i use ashore.

Sll sockets are for modest piwer supply on isolated sppliances.

Only real item is the SS oven grill.

Though reconfitionef, i will carefully check its isolation (wires/bofy frame)


Yes, I'll install a galvanic isolator, not an isolation transformer, too expensive/big for 32A
Thanks
PS
I put back the green wire up to electric panel...
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