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skinner76 08-30-2007 08:58 AM

Garage Wiring Problem
I am planning on installing a flourescent light in my detached garage as well as a lightswitch to control a patio spot. When I inspected the wiring I noticed several things that I think may be problems, and I would like some advice before I proceed.

There are 2 circuits in the garage. Both come into the garage via an underground conduit (run under concrete walkway) through UF-B 14/2 cable.

One circuit is wired with a mix of NM 12/2 and NM 14/2. (I know this is not ideal, but it's already there) This circuit contains 6 receptacles (all 15A) and a light bulb socket. It connects to a 20A breaker. How much of a problem is this set up? Do I need to replace the breaker with a 15A, or the NM12 with NM14? As far as I can tell the circuit has existed like this for the last 20 years (I've only owned the house for 4 yrs). Oh, don't know if this is impt, but the service coming into the house was upgraded from 110 to 220, years before I bought the house.

The other garage circuit contains a spotlight, a patio light and 6 highhats in the house. As far as I can tell it is all wired with NM14/2 and goes to a 15A breaker. This is the circuit that I would like to add a flourescent light to, and also add a switch that controls the patio light -- I'll be doing this in the garage with NM14/2. I think this circuit is fine, but is there anything I should know, before I begin this part of the project?

Any advice would be much appreciated. Thanks

darren 08-30-2007 04:33 PM

Hi there

Your first question about the mix of 14/2 and 12/2 on a 20A breaker. I would change it out to a 15A breaker, #14 is not allowed on a 20A breaker it is only rated for 15A.

Are you sure that second circuit controls stuff in the house as well as in your detached garage. Not sure if there is a code violation with this but I would not want this i rather have all my garage stuff on one circuit and the house on a seperate circuit.

You should be good to go with what you want to add as well.


wooderson 08-31-2007 05:15 PM

If I'm correct it sounds like your 15 amp lighting circuit has a lot on it. One smart thing to do is do a load calculation to determine if you "have enough room" on that circuit. Add up all of your lighting wattage(whatever the fixture is rated for) and divide by 120 this will give you amps. Also, make sure that you stay below 80% of the breaker capacity. 15a=12a.

skinner76 08-31-2007 09:01 PM

Thanks for the responses. I'm going to take your suggestions and advice.

chris75 08-31-2007 09:26 PM


Originally Posted by wooderson (Post 60725)
Also, make sure that you stay below 80% of the breaker capacity. 15a=12a.

I see this statement alot, and all I can ask is WHY?

Stubbie 08-31-2007 11:00 PM

The NEC does not allow 2 branch circuits to serve the garage.... only one branch circuit is allowed to enter the garage from the house panel (NEC Art.225.30) or one feeder.

The single branch circuit must also have a disconnect very soon after it enters the garage. In the case of a 15 or 20 amp branch circuit a simple toggle light switch will suffice. It must be labeled as the disconnect for all power to the building.

So one of the branch circuits must go to be code compliant. Or feed the garage with a multiwire branch circuit or feeder to a sub-panel.

I suppose wooderson is referring to the 80% for a branch circuits permissible load when it serves more than one receptacle or outlet for cord and plug equipment. However there is no requirement or way to really control what you or someone else plugs into the branch circuit. The only time 80% is required is for continuous loads. The NEC is an installation standard not a products hair dryers are rated 15 amps and vacuums are rated 15 amps.... in other words 100% of a 15 amp circuit. I'm not sure why they just don't say recommended vs permissible.


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