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Old 02-05-2009, 08:14 PM   #1
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I need a little help with this one guys. Here's the situation: I just installed a disconnect box with two SP breakers and seperate ground rod at the sea wall between my lake house and my boat dock. The disconnect box has separate ground and common terminal bars and the common bar is insulated from the metal of the box. There is an existing 3 W/G line from the house supplying two 120V circuits to the new disconnect panel's two buses, the common wire goes to the common bus bar and the ground wire to the ground bus bar. The Ground bar is also Grounded to the metal on the dock and to the new ground rod. The two 20A GFCI breakers are installed with their fixed white "panel common" attached to the common bar. (NOTE: The intent of the previous home owner was to have two separate 120V circuits on the dock, not to have 240V)

The two load wires from the dock are of course connected to each breaker's load side respectively. The "load common" connectors are tied to the one common wire going out to the dock. With this wiring in place both of the breakers trip immediately when turned on. I know there is no ground fault on the load side because I replaced that wiring.

What follows may trigger a thought from one of you guys. I can disconnect the load common from one of the breakers and the other breaker will work perfectly. If I do this with the other breaker that the opposit one will also work. If I touch the two load common wires together both breakers will trip.

I'm beginning to think that this problem may be related to a phase issue at the house panel. I haven't pulled the panel cover yet but the two breakers are one on top of the other so they are probably on different phases. Does anyone think this is the problem? If so I can simply move the house breakers around and solve it. The other possibility do I need separate common wires to the dock. How about using a DP GFCI Breaker

As always, I will appreciate any help I can get on this.
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Old 02-05-2009, 08:24 PM   #2
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Gfis detect a 5ma current imbalance, by crossing the commons, current traveled down a separate neutral, current was flowing through the hot of the gfi, but not back on the neutral of it.

You need two separate neutrals for these circuits.

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Old 02-05-2009, 08:50 PM   #3
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For the GFCI's to work properly, you must have two separate neutrals, one to each load.
You must make sure that the LOAD side of the GFCI breaker is wired so that its hot and neutral feed the same load.

A double-pole GFCI will not work in your case, since you are not running 220V loads, and would have different currents in each leg, so it would also trip.

You could just use GFCI receptacles, mounted in weatherproof boxes of course.

FW
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Old 02-05-2009, 09:01 PM   #4
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You have a multiwire branch circuit running out to the docks using a shared neutral. You cannot use two single pole gfci's for a multiwire branch circuit. They will immediately trip. One gfci is seeing zero amps on its hot wire but showing neutral current and trips.
These are your options if you keep the multiwire.....
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Old 02-05-2009, 10:05 PM   #5
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Originally Posted by KE2KB View Post
For the GFCI's to work properly, you must have two separate neutrals, one to each load.
You must make sure that the LOAD side of the GFCI breaker is wired so that its hot and neutral feed the same load.

A double-pole GFCI will not work in your case, since you are not running 220V loads, and would have different currents in each leg, so it would also trip.

You could just use GFCI receptacles, mounted in weatherproof boxes of course.

FW
Using two GFCI recepticals seems to be a good solution. Can I put them on the load side of the disconnect box (they would be sharing the same neutral) and then replace the GFCI breakers with regular breakers? Of course I would use a weather proof box
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Old 02-06-2009, 08:07 AM   #6
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First I really appreciate your response to my question.

Using two GFCI recepticals seems to be an easy solution. I would install them as stand alone on the line side of the disconnect box (they would be sharing the same neutral from the house, so I hope that's not a problem). Then I would replace the GFCI breakers with regular breakers using a weather proof box. Does this make since to you?
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Old 02-06-2009, 12:29 PM   #7
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That's fine. A gfci receptacle wired to the line terminals only sees what is plugged into it. Sharing the neutral after that doesn't matter. And yes this would be the cheapest as gfci with a double pole device is expensive.

You should have a normal double pole breaker though instead of two single poles so that both hots are disconnected when working on the branch circuits.
Also pigtail the neutral to the gfci's.
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Old 02-06-2009, 07:09 PM   #8
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Thanks Stubbie. You have been very helpful!
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Old 02-07-2009, 09:11 AM   #9
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Originally Posted by KE2KB View Post

A double-pole GFCI will not work in your case, since you are not running 220V loads, and would have different currents in each leg, so it would also trip.
Not true - a double pole GFCI would work fine.
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Old 02-07-2009, 01:56 PM   #10
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A 2 pole GFI breaker that has a neutral connection (most of them do) will work with unbalanced loads. Like two separate 120 volt circuits.

A 2 pole GFI breaker that does not have a neutral connection must be used for 240 volt loads only. Neutral current will be seen as a fault, and the breaker will trip.

Rob
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Old 02-07-2009, 02:24 PM   #11
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Quote:
Originally Posted by micromind View Post

A 2 pole GFI breaker that does not have a neutral connection must be used for 240 volt loads only. Neutral current will be seen as a fault, and the breaker will trip.

Rob
Does that beast even exist? I figured that all gfci breakers required a neutral connection for the electronics in the unit to function?
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Old 02-07-2009, 02:27 PM   #12
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Quote:
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....A 2 pole GFI breaker that does not have a neutral connection must be used for 240 volt loads only. Neutral current will be seen as a fault, and the breaker will trip...
I have never seen a 20 Amp 2-pole GFI breaker without a neutral connection. The only time I have seen such a breaker was a 60 Amp monster.
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Old 02-07-2009, 02:44 PM   #13
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The only time I have seen such a breaker was a 60 Amp monster.

What 60a 240v volt load required gfci protection?
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Old 02-07-2009, 02:52 PM   #14
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Most hot tubs are 50a & require a 50a GFCI breaker
And yeah they are expensive - had to but one at the last house
And then had to buy another one at this house for a new hot tub
I have seen some 60a hot tubs, so that would be one item
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Old 02-07-2009, 02:56 PM   #15
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Quote:
Originally Posted by Scuba_Dave View Post
Most hot tubs are 50a & require a 50a GFCI breaker
And yeah they are expensive - had to but one at the last house
And then had to buy another one at this house for a new hot tub
I have seen some 60a hot tubs, so that would be one item
Never wired a hot tub that was not 120/240, that means it had a neutral connection.

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