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Old 02-25-2009, 12:27 PM   #1
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Double 40 AMP GFI Breaker ok for subpanel?


I'm wanting to run install a subpanel in my single car garage to replace all of the old two conductor outlets that are out there and the current garage door opener outlet that connects through the ceiling to an upstairs outlet. I currently have a dual 40 amp GFI breaker installed in my main box connected to 6/3 wire that previously ran through the garage to a manual disconnect for a hot tub which is no longer there.

Is this breaker acceptable to connect a subpanel in the garage?
If so, what would I use as a main in the subpanel, another dual 40?

In the garage, I was thinking about the following coming off of the subpanel:

- One 20 Amp circuit with 6-8 duplex outlets (including a GFI)
- One 15-20 Amp circuit feeding 3 overhead lights/outlets on a switch
- One 15-20 Amp circuit feeding an overhead outlet for the garage door opener.


Thanks,

Mike

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Old 02-25-2009, 01:27 PM   #2
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Double 40 AMP GFI Breaker ok for subpanel?


You only need to use a main lug only sub panel. 2P40 will work. 8/3 with ground service cable You need to isolate the grounds and neutrals in the sub panel.

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Old 02-25-2009, 01:59 PM   #3
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Double 40 AMP GFI Breaker ok for subpanel?


You can reuse the 40, but since you have 6/3 why not go and buy a 60 amp double pole breaker?
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Old 02-25-2009, 03:47 PM   #4
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Double 40 AMP GFI Breaker ok for subpanel?


Or just use the 6-3 with the 40a breaker
If you need more power later you can buy a 60a breaker
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Old 02-26-2009, 10:48 AM   #5
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Double 40 AMP GFI Breaker ok for subpanel?


My 2 cents.

Ditch the 40 amp gfci breaker. Sell it on e-bay. You have 6/3 wire with ground so stick in a 2 space 70 amp square d (HOM24L70f/s sub panel main lug only. Easily found at Lowes or an electrical supply. This is if you do not ever want 240 volt loads. If you think you might want a small 240 volt heater someday for the garage get a 125 amp (HOM48L125f/s)....or equivalent in another brand.

The 70 amp has 2 full size spaces that you will install 2 single pole tandem breakers giving you 4 120 volt branch circuits...ie...the 24 after HOM.

The 125 amp gives you 4 spaces to install tandem single poles to provide 8 120 volt circuits or you can install one double pole for 240 volts and 2 tandem single poles for 4 120 volt branch circuits.

Feed either panel with the 6/3 with ground. You need to separate neutral and ground..so be sure you know how to do this. With square d you do not install the green screw in the neutral bar and add the ground bar kit to the panel. Very simple.

Install a 60 amp double pole breaker in the main panel to protect the 4 wire feeder to the sub-panel.

As for gfci.... a breaker costs around 30 to 35 bucks to protect your outlets or an option is 15 bucks if you install a gfci receptacle first in the run and protect regular receptacles off its load side terminals.

Tandem breaker


Just my opinion.
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Old 02-26-2009, 11:03 AM   #6
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Double 40 AMP GFI Breaker ok for subpanel?


Thanks for the great advice. Sounds like ditching this breaker is the way to go. I was really only considering using it due to a bit of extra concern about working inside the breaker box. But, from what I'm reading, flipping the main breaker makes it safe enough to do that, so I should be good.

The only other question I had was do I need to separate the neutral and ground at both ends, or just at the subpanel? I've not sure that I've seen a definitive answer on that one.

Mike
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Old 02-26-2009, 11:18 AM   #7
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Double 40 AMP GFI Breaker ok for subpanel?


The feed at the subpanel as well as everything else in the subpanel has neutral and ground separated.

Neutrals and grounds are combined at the main panel. For a GFCI breaker at the main panel its branch circuit or feed neutral goes into the breaker and the breaker has a neutral conductor to connect to the panel bus. For a regular breaker at the main panel the feed neutral is connected directly to the panel bus.

One obscure detail: If the main disconnect switch which can be a main breaker is in a box of its own, that box is the main panel and what you think of as the main panel full of breakers is really a subpanel where neutrals and grounds need to be kept separate.
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Old 02-26-2009, 11:26 AM   #8
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Double 40 AMP GFI Breaker ok for subpanel?


Quote:
Originally Posted by tigereye View Post
Thanks for the great advice. Sounds like ditching this breaker is the way to go. I was really only considering using it due to a bit of extra concern about working inside the breaker box. But, from what I'm reading, flipping the main breaker makes it safe enough to do that, so I should be good.

The only other question I had was do I need to separate the neutral and ground at both ends, or just at the subpanel? I've not sure that I've seen a definitive answer on that one.

Mike
HI Mike

I would guess that the panel where your 40 amp gfci is located at present is your service equipment if it has the main breaker for your home located in it. If not then you probably have a disconnect out by the meter. If the panel with the 40 amp gfci has the main disconnect neutral and ground a bonded there and that is the way it should be.

Any way turn that main disconnect off when you get ready to connect the double pole breaker. In it is located in the panel remember that the main lugs on the main breaker are always hot but the busses will be deenergized that the breakers connect to.

Here is a diagram of what your going to be doing...just remember different manufacturers use somewhat different methods to separate neutral and ground so ask bck if you get confused.
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Double 40 AMP GFI Breaker ok for subpanel?-4-wire-feeder-same-building.jpg  
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Old 02-26-2009, 11:28 AM   #9
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Double 40 AMP GFI Breaker ok for subpanel?


Quote:
Is this breaker acceptable to connect a subpanel in the garage?

Yes


Quote:
If so, what would I use as a main in the subpanel, another dual 40?
Any breaker/no breaker...doesn't matter in your application. More than six breakers and you need a main./...... of any size.



Most of us, being electricians, would install a standard 2 pole 60 amp breaker and a 12 to 20 space panel in the garage. We are manly men and like to over power things

Neutrals and grounds together at the service, separated at the sub panel.

CAUTION:

Even with the main breaker off, test and be aware. Look and see where the power comes in from the meter. There is sometimes energized bus/wires exposed even though the main is off.

Last edited by 220/221; 02-26-2009 at 11:31 AM.
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Old 02-26-2009, 11:48 AM   #10
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Double 40 AMP GFI Breaker ok for subpanel?


Ah, I missed that it was GFCI
I'd use a 60a too
I used a Square D 100a panel in my pool cabana & fed w/60a
It was fairly inexpensive at HD
I have 3 panels & all are Square D - makes it easier to swap breakers between panels if needed
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Old 02-26-2009, 12:34 PM   #11
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Double 40 AMP GFI Breaker ok for subpanel?


One thing I noticed that hasn't been defined here, is this garage attached to the house or is it detached? If its detached, code requires that you have a MINIMUM 60 amp disconnect at the detached structure. This can simply be a 60 amp breaker or a 100amp main breaker panel. It does not matter the size of the supply breaker in the main panel. This rule does not apply if its attached, its more or less a good idea to have a main breaker in the sub panel.
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Old 02-26-2009, 02:11 PM   #12
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Double 40 AMP GFI Breaker ok for subpanel?


Quote:
Originally Posted by theatretch85 View Post
One thing I noticed that hasn't been defined here, is this garage attached to the house or is it detached? If its detached, code requires that you have a MINIMUM 60 amp disconnect at the detached structure. This can simply be a 60 amp breaker or a 100amp main breaker panel. It does not matter the size of the supply breaker in the main panel. This rule does not apply if its attached, its more or less a good idea to have a main breaker in the sub panel.
It's attached. The total length of the run between the boxes is around 30 feet.

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