garages, GFCIs / understanding better.

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jbwhite

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I want to thank all of you who answer questions in this forum. especially charlie. he always has a very informitave post in reply to an issue. Is that enough butt kissing to get some help trying to understand this issue better. :p

I have a house with a detached garage. I want to install a 12/3 UF cable so I can put a couple lights and a couple recs out there. I would really like to have two seperate circuits out there, and I would like both circuits to be gfci proteced.

1. Do I need a ground rod at the garage?

2. Can I use a two pole gfi breaker?

tks in advance for your replys.
 
Re: garages, GFCIs / understanding better.

No and yes.

A single branch circuit (mulitwire branch circuit does not require a grounding electrode system when installed a separate structure. See 250.32(A) Exception.

The gfci device can be installed at the main structure or as the required disconnecting means at the garage.
 
Re: garages, GFCIs / understanding better.

Hate to bother but I want to expand my question.

Will the two pole gfi trip on normal line to neutral use? ie two 120 volt circuits feed from one two pole gfi breaker?
 
Re: garages, GFCIs / understanding better.

I may be wrong about this, but I believe a GFCI works by placing a current transformer around all hot and neutral wires, somewhere internal to the GFCI device. If all is well, any current leaving on any of these wires will return via one or more of the other wires. The net total magnetic field detected by the CT will be zero. But if there is a ground fault, so that some current returns to the source via the EGC, via the ground rod, or via some unfortunate person, then the net magnetic field seen by the CT will no longer be zero, and it will trip if the discrepancy gets too high.

So I believe the short answer to your second question is "no." If there is a single 120 volt load running on one phase, and nothing on the other phase, the CT internal to the GFCI will see the same current leaving one wire and returning on the other wire. So the GFCI will not trip.
 
Re: garages, GFCIs / understanding better.

I am not a huge fan of putting GFCIs in a panelboard.

The problem is that when it trips, it may not be obvious what happened. I think it is better to be able to push the reset button right at the outlet.

I dislike feeding downstream outlets with the GFCI feed through pigtails for the same reason.
 
Re: garages, GFCIs / understanding better.

Gfci protection on the line side of the lateral for uf 120V or less w/ overcurrent max 20A is only required for a cover requirment of 12 inches.(300.5)Get the shovel out for another 12 inches and use two gfci receptacles.You can also wrap it to a messenger and fly it over.
 
Re: garages, GFCIs / understanding better.

I agree. A double pole GFCI costs a lot -- usually much more than the premium for two GFCI receptacles. I'd just put a reguler double pole 20A breaker at the house, install a double pole 20A switch at the garage where the conductors first enter, and then split into two separate circuits with a GFCI as the first receptacle on each.

To have the house to garage feeder non GFCI protected, you have to use direct bury cable at 24", PVC conduit at 18", or rigid conduit at 6".

[ December 02, 2005, 11:16 PM: Message edited by: suemarkp ]
 
Re: garages, GFCIs / understanding better.

A agree that you are better off to use receptacle or blank face GFCIs in the garage. A 12/3 with ground UF cable is considered to be a single branch circuit for the purpose of using light switches as building disconnects at a deteched garage.

By the way, some places such a Parma, Ohio require that the receptacle for the garage door operator be GFCI protected on the basis that the operator has grounded metal within reach as well as that METAL garage doors are popular for security reasons. In this case you would need to feed the ceililng receptacle off of a wall mounted Blank face GFCI or receptacle GFCI.

Using GFCIs that are close to the load has a lot of advantages. Among them are troubleshooting a problem and less nuisance tripping due to wiring capacitance or wetness.

Also, a local ground rod helps with things such a static electricity and that 97% of lightning damage in a telephone cable plant comes from silent lightning and invisible lightning. Since telephone cables need a 300 volt rating to reliably carry ringing current the same thing can be said about building wiring. If you have metal siding or any metal doors or metal siding on your garage a ground will help stop a little bit of lightning from doing a lot of damage.
 
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