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Old 06-04-2019, 10:54 PM   #1
DDW
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Double pole breakers on genset/shore power

My boat is wired using two double pole breakers feeding the AC panel, with a lockout: either the genset (50A) or the shore power (30A) can be on, but not both. I am intending to reconfigure it with a 2 pole rotary switch to choose between generator and shore power. That done, is there any reason to have a double pole breaker feeding the panel from the rotary? Or can I just connect the neutral and have a single pole on the line?

The genset has a double pole 50A in its output. The shore power has a double pole 30A near the cord connection (these are in addition to the ones at the AC panel). There is reverse polarity detection on both. What hazard is the second pole at the panel protecting against? Originally, since the breakers were used to switch sources, two poles were necessary for isolation, but isolation would be enforced by the rotary which switches both L and N. My sailboat is wired this way, only one pole for the panel.

Beyond something I haven't thought of, the only problem with this scheme is I must choose between a 30A and a 50A single pole breaker to feed the panel. I would go with a 50A to accommodate the additional power from the genset, as the shore power already is limited to 30A by the double pole near the cord connection.

Does the ABYC prohibit this?
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Old 06-04-2019, 11:08 PM   #2
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I think you'll need to stay with double pole switches. The generator (or inverter) will tie the ground to neutral on the boat, so does the shore power at the dock. Neutral and ground should only be connected once at the "source" of power.
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Old 06-04-2019, 11:12 PM   #3
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Why does that change in my scheme? Either the genset neutral or the shore power neutral will be connected to the panel, not both - the rotary switch prevents it. If they have a ground tie before the panel, then it has this problem now, the double pole breakers do nothing to change that?

It seems like the only thing the second pole adds is to disconnect neutral in addition to line in the event of an overcurrent fault. This might not occur if the panel breaker tripped before the source genset or shore power breakers.
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Old 06-05-2019, 02:16 AM   #4
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Since your rotary switch is switching both line and neutral, there is no reason to have a circuit breaker doing the same thing.

A single pole circuit breaker will work fine.

We use two pole circuit breakers with a interlock to switch between generator and shore power because they in one device switch both line and neutral, and provide overcurrent protection. Two pole breakers are an easy foolproof installation methodology.
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Old 06-05-2019, 04:16 AM   #5
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What about a reverse polarity situation while plugged into unfamiliar shore power?

I like the breaker interlock -- keeps it simple and foolproof.

I guess I'm not sure what problem we're trying to solve, or I'd try to help more.

Cheers!

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Old 06-05-2019, 07:39 AM   #6
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While your system will work, I believe it is required to use a 2 pole breaker.
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Old 06-05-2019, 08:24 AM   #7
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First, the rotary switch is not a circuit breaker, so you will still need 2 pole breakers for the shore power and for the generator. You are not gaining anything but spending more money.
The interlocked breaker setup is simple, fool-proof, and cheap.
What do you hope to gain?
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Old 06-05-2019, 08:42 AM   #8
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Without a current and future overall electrical plan....it's hard to comment.


What has been provided so far, I am in the "why change" camp.
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Old 06-05-2019, 08:48 AM   #9
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Shore power is protected at your entrance, and the genset is protected at its source. No need for more main feed overcurrent protection. Its just that simple.
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Old 06-05-2019, 10:26 AM   #10
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Please read the OP. There is already a 2 pole breaker at the genset and shore cord entrance. Then through the rotary and an additional breaker into the panel. "Why change" might be the subject of another thread, but not this one, it is not because I have nothing else to do.

I found an extensive discussion on another board from awhile back. There is apparently controversy over two vs. single pole breakers among the standards setters, and no clear advantage either way - both have plusses and minuses. The main safety concern is reversed polarity. The best solution to that seemed to be a double (or 3) pole breaker, with one pole used to break the line, and the other a small amp value breaker between the neutral and ground. If polarity is reversed current flows in this breaker, trips it along with the line (and neutral if 3 pole).

I'm going with the single pole for the panel.
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Old 06-05-2019, 11:39 AM   #11
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Hi DDW,

Sorry. I misread/misunderstood your original post w.r.t the existing 2-pole breaker. I thought it was off-boat at an extension of some kind. Sorry, again.

Can you elaborate as to the minus(es) of a 2-pole breaker, other than additional real estate, additional cost, and maybe some more wiring involvement? I'm not sure that I see the risk.

I can't say I've ever seen someone put a low-amp breaker between the neutral and grounding conductors. I understand the idea. But, an ELCI breaker seems like the perfect tool to guard against that situation. And, it also guards against a bunch of other dangerous stuffs.

Cheers!
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Old 06-05-2019, 01:05 PM   #12
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Much easier to start with a schematic or wiring diagram and then talk to it. Rather than making the verbiage the wiring. I do realize this website makes easy uploads more difficult.
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Old 06-05-2019, 02:55 PM   #13
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Yes, a ELCI or even a GFI breaker does much the same thing, though perhaps with more nuisance trips. The concern about double pole is the idea that the neutral wire should never be interrupted, as this can leave the equipment at line potential. A breaker in the neutral introduces a point of failure for this to occur. Very rarely are double poles used on branch circuits. The neutral is supposed to be at or near ground potential so there should be no danger from it - except in a reversed polarity circuit. A pretty good discussion of it here, look at post #45.

Takes awhile to draw up and post schematic, and this is a pretty simple circuit: double pole breaker, rotary switch, single pole in series.
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Old 06-06-2019, 12:51 AM   #14
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Hey DDW,

Thanks! That was a fun read.

In my own estimation, I think ABYC got this one right. I agree that the pluggagble nature of boats exposes them to hot-neutral reversals in a way that hard-wires fixed structures are not exposed, changing the balance of risks, and making a dual pole breaker worth the tiny risk of a neutral disconnect at exactly the breaker, especially since that would be apparent really fast by nothing working.

I've had no nuisance trips in about 4 years of ELCI usage on my boat and regularly run power tools and vacuums, etc. Maybe because itbtakes 6x as much current to trip one as a household style GFCI.

The only thing I've noticed is that the curve for my 30A Blue Seas ELCI is blows faster than my old school 30A main. It will tolerate a modest overload for less time before popping, e.g. 2 AC units + Microwave.

Cheers -- and thanks again!
-Greg
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Old 06-06-2019, 10:18 PM   #15
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Both of my shore power circuits, (and the genset input) have reverse polarity detection. I think even the ABYC allows a single pole with polarity detection. The interesting thing about the neutral to green wire breaker is it would not let you operate with reversed polarity, while a two pole would. I think most GFI/ELCI breakers would not either.
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Old 06-07-2019, 01:02 PM   #16
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Hey DDW,

Faur enough.

For whatever it might be sorry bro someone, my Blue Sea ELCI is double pole and has a reverse polarity indicator LED, but does't trip (or fail to set) under reverse polarity conditions.

Cheers!
-Greg
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