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Old 06-30-2013, 04:37 AM   #1
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2 pole or 3 pole power transfer switch for 240v?

I'm upgrading to 240v....though its entirely possible the boat was 240v in the past as the wiring is 4 wire 240v type coming in, plugs are, etc. But....the current main panel was set up for only 120v.

I have a 2 pole manual power transfer switch on the boat that is 3 position. Gen/Off/Shore. Searching the internet turns up mostly home generator/service info.......and there is argument there over whether the transfer switch can be 2 pole interrupting the hot wires with shared neutral in the panel bus........or whether the neutral also has to be switched. Apparently it depends on code and whether your generator is portable, or over a certain KW output.

Obviously switching to a 3 pole switch could add another $500 plus dollars.

I don't even have a generator on board yet, as the previous owner took it off the boat before it was repo-ed, but...can anyone tell me what is correct in a marine application? Can the 2 hot wires be switched but the neutral shared in the panel?

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Old 06-30-2013, 06:52 AM   #2
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The neutral and ground are joined at the SOURCE.

Dockside it is somewhere in the boat yard and 4 wired are carried aboard.

An inverter or noisemaker is a source , so again 4 wires are used .

Why not use 240V 50A range sockets and plug?

It requires 3 sockets , one for the external source and one each for the inverter and noisemaker.

The plug is the boat.
The RV folks have better plugs with molded handles to make Pulling easier. $15 instead of $6 or $7.

As all is inside home cheapo is a fine source and $50 , not $500 will do the job safely and to code..
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Old 06-30-2013, 09:41 AM   #3
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Hi FF...thanks for the reply and suggestion...its an interesting one and would work. But let me see if I follow your electrical knowledge in another way, or am I twisting it?

If they are all 4 wire at the source, and ground and neutral are connected at the source...and I do have 4 wire on the boat...

4 wires come aboard at the plug from shore power. They travel forward, and the 2 hot lines come into a 2-pole rotary switch that says Gen/Off/Shore. 2 continuation wires leave this switch and go to the circuit breaker panel and attach to the hot lugs (connecting the circuit when the switch is turned to SHORE).

The other 2 wires (neutral and ground) go into the circuit breaker panel and meet their respective bars.

Now another 4 wires comes from my non-existing generator. The gen is gone, but the wiring is still there. 2 of those wires, both hot, head to the rotary switch. When the switch is positioned to GEN, they connect the circuit to the circuit breaker panel by those same wires mentioned 2 paragraphs above.

The other two wires (neutral and ground) go to the circuit breaker panel on their respective bars.

So there are two neutrals and two grounds going to the bars in the circuit panel. Is what I am describing a no-no?
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Old 06-30-2013, 03:00 PM   #4
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Sounds like if they are connected and not switched the ground at the noisemaker and inverter will also be at the bus bars with the shore power.

This is a big no no as the neutral will frequently NOT be at Zero V and if connected to ground on board can end up in the water or on DC or the batteries if they are grounded.
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Old 06-30-2013, 09:23 PM   #5
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gotcha....and thanks. I'll take that as a no. And no. And no. lol
Is there a difference between the rotary switches and a 3 position knife switch? The rotary switches are very expensive, and the knife switches aren't. Just curious. I may take your suggestion and just use a plug and different receptacles until I decide a different course.
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Old 06-30-2013, 11:01 PM   #6
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You need to switch the neutral in a marine application.
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Old 07-01-2013, 09:41 AM   #7
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Look in Boats and Harbors , one of the advertisers has rotary switches (huge) for about $200.
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Old 07-01-2013, 10:38 AM   #8
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This question has been answered but maybe not definitively.

Four wire, 240V systems need to break the neutral when it is part of a system connecting two different supply sources such as shore power and a genset. This can be done with three pole breakers and a slider bar or a three pole double throw switch. You break the neutral so that the source that is disconnected cannot be back fed through its neutral.

If all you are doing is protecting one supply system, such as the breaker on the shore power box, it only needs to break the hot(s).

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Old 07-03-2013, 12:20 PM   #9
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Thanks for all the replies...I will look for a 3 pole switch.
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Old 07-12-2013, 09:41 AM   #10
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From our for sale section,

Blue Seas Power Source Switch P/N 9093
Blue Seas power source selector switch. Off + 2 positions. Rated Voltage 600. Amps 65. 120//240VAC 65A. 4 poles. West Marine # 5426689. Switch Size S1.. New in Box. Change of plans. Lowest price I have seen, $ 327. sell for $ 200. + shipping.
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Old 07-12-2013, 07:08 PM   #11
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You know...I just bought a knife switch...3 pole, 100 amp. I think I paid $40 for it shipped. Just couldn't justify the rotary switch prices. But I am glad I asked here because with the explanations I have a better understanding of what is going on between the different circuits. But I appreciate you posting that for me.

Thanks!
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Old 07-13-2013, 05:43 AM   #12
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.I just bought a knife switch...3 pole, 100 amp.

I hope it will be in a covered box where it wont be someones hand grab!
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Old 07-13-2013, 08:35 AM   #13
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lol, no it will not be in a position to just grab by anyone.
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