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Old 05-24-2011, 08:07 PM   #1
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garage lighting circuit


Can someone please answer me this, background info first:

Background:
I'm wiring my garage with a 100 amp subpanel, I'm following 2008 NEC. Inspection tommorrow, I need to work with the materials I have. For the time being, I'm keeping the wiring basic with plans to add more circuits later, so I'm covering an outdoor receptacle, a few workshop receptacles, a receptacle for the garage door openner and 2 switch operated lights. One light will be operated by 3-way switch with one switch in the house. The other will be a hanging flourescent cord and plug fixture plugged into a ceiling fixture. In list form:

- 1 outdoor duplex receptacle
- 1 wall with a line of receptacles in the workshop
- 1 receptacle for the garage door openner
- 1 switch operated receptacle for the indoor flourescent light
- 1 outdoor light operated by 3-way switch, 1 switch in the house and 1 switch in the garage.

I've run my travellers and whatever you call them through my conduit. As I said, I have to use what I have. I've run 2 UF cables of 10-2. No budget for a proper 12-3 UF cable which would make my life easier. So it's long enough to reach the switch inside the house and get through the wall in the garage. I have 14-3 NM cable for in the garage which I can splice to the UF inside a junction box for the remainder of the run to the garage switch.

So obviously I'm wanting this on a 15 amp circuit while everything else wants to be on a 20 amp circuit.

Here is my question: If I have this light on a dedicated circuit without any receptacles, is GFCI still required?

If it's going to be required, given the materials I have, I'll have to run it off the receptacles circuit and do 2 runs of 12-2 NMB from the UF cable to the switch. I'd rather avoid this because I was hoping to have the GDO on a dedicated circuit, using the 12-2 to the switch would probably force me to feed the GDO off the wall receptacles.

Follow up question: If the outdoor light does not require GFCI if it is on a dedicated circuit, which I suspect is the case, is it exempt from AFCI? (From searching I think my understanding is that GFCI applies to receptacles while AFCI applies to outlets, which encompases receptacles and other things like smoke detectors and light fixtures)

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Last edited by WillK; 05-24-2011 at 08:23 PM.
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Old 05-24-2011, 09:22 PM   #2
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garage lighting circuit


you can not use two cables for 3 way switching if it passes thru any metal-stud/pipe/boxes. Here you must use 3 wire.

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Old 05-24-2011, 11:18 PM   #3
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Er.. okay. So maybe I'll just do a switch in the garage I guess and leave cables so I can use them later to pull 14/3 if I change my mind later this month..

But for my own curiousity, what difference does it make to 3 conductors if they are inside the same plastic sheathing or not? And for that matter wouldn't it be allowed to run 3 THHN conductors?

Regardless, a 15A circuit in the garage going to an outside light with a switch inside, am I correct that no GFCI or AFCI required?

And if I put the inside ceiling receptacle for the light on the same circuit, is it permited for the GFCI after the switch?
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Old 05-25-2011, 12:04 AM   #4
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garage lighting circuit


Quote:
Originally Posted by WillK View Post
Regardless, a 15A circuit in the garage going to an outside light with a switch inside, am I correct that no GFCI or AFCI required?
Correct - 210.8(A)

Quote:
And if I put the inside ceiling receptacle for the light on the same circuit, is it permited for the GFCI after the switch?
As far as I know, if you have a receptacle in the garage, it must be GFCI protected. Not sure about the "after the switch" question.
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Old 05-25-2011, 12:35 AM   #5
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Quote:
Originally Posted by WillK View Post
Er.. okay. So maybe I'll just do a switch in the garage I guess and leave cables so I can use them later to pull 14/3 if I change my mind later this month..

But for my own curiousity, what difference does it make to 3 conductors if they are inside the same plastic sheathing or not? And for that matter wouldn't it be allowed to run 3 THHN conductors?
its an obscure code section, actually two sections that work together(or not).
Essentially what is says is that all conductors of a circuit must be in one cable or pipe(so yes thhn would work). It is because of induction and eddy currents created in metal. There is an "exception" using only certain cables(NM), that if completely non metallic (romex, wood studs, plastic boxes) that you are allowed to use more than one piece of romex for a circuit(note this is subject to some intereptation, some say that there is no exception to the rule for all circuit conductors to be run together. its one of those things that the code doesn't say you can, but doesn't explicatively say you can't)

I'm sorry I don't have the code sections in front of me, but this topic has been hammered out pretty throughly on this and other forums before.


edit: ever wonder why 2 wire w/ground romex is flat? three wires twist into a nice round shape. why 3 wire is round and twisted at that certain rate? these cables are designed to work as a unit, for many purposes one of which is to reduce induction/noise/eddy currents. this is one reason that the code does not allow you to modify cables or use them for purposes not listed in the code. cables have been engineered in so many ways, that you just can't contemplate them all if you are trying to use it outside of the manufactures instructions.
If you fail to run all circuit conductors in the same path/pipe/cable, you can get many undesired effects: eddy currents, high impedance, radio interference, oh help me out guys list the other effects. eddy currents could build up enough in metal objects enough to be dangerous.
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Last edited by Saturday Cowboy; 05-25-2011 at 12:53 AM.
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Old 05-25-2011, 01:01 AM   #6
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300.0 B 3 300.20


this is a thread that will get you more confused http://forums.mikeholt.com/showthrea...ay-switch-loop
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Old 05-25-2011, 06:05 AM   #7
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Sooo... how about if I direct buried my UF next to the conduit? Although I'd still have to come up with protection from physical damage for the riser.

Edit- the question remains out of curiousity, but I think that might not work since I dug the trench to 21" and direct buried UF requires 24" if I recall.

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Last edited by WillK; 05-25-2011 at 06:24 AM.
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