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darlingm 12-02-2011 01:30 AM

Attic - Replacing electrical - Positioning, how many boxes, checking understandings
In "Attic wiring - ceiling light uses 14/2 cable without ground", I discussed that my attic electrical supplies only the ceiling lights, and was done with 14/2 cable without ground. After many helpful responses, I decided I could live with ungrounded ceiling lights and light switches. (Note that the rest of the house was redone before we purchased it, and looks good, with new romex, grounded, and GFCI's near water. That re-wiring job ignored the attic.)

Sigh. Today, almost done with my project, I found several feet of scorch marks on the underside of a fiberglass batt covering one of these wires. The old wiring is fiber/paper wrapped romex, and that stuff's only rated for 50C. While rewiring the ceiling light yesterday, found that some idiot decided to install 90C ceiling light units throughout the house. Previously bagged and threw out all the other batts under bad lighting conditions, could have easily missed many more scorch marks.

After finding what only didn't become an attic fire due to a small temperature difference, or lack of oxygen underneath the batts, I've decided I'm running all new wire in the attic.

So, I'm looking for some pointers on effectively running two new circuits into the attic. (Some of this is reassurance that I'm thinking along the right lines.)

Question 1 - Nothing is in the way, because there's no insulation at all now. Should I run the electrical and have junction boxes along the attic "floor", or should I run the electrical and have junction boxes along the attic "ceiling"? I've seen some people say to run everything along the floor, so the electrical is insulated against the summer heat. (I live in Michigan - not too hot, but we do sometimes hit 100F.) I've seen others say to run everthing along the ceiling, so everything is more visible and accessible, and only going into the insulation when coming up from the basement or down to a light or light switch. I think the floor will be faster, and would need half as many junction boxes if question #2 goes my way.

Question 2 - Assuming that I'm running everything along the attic floor, should I use a deep junction box at each light that the light hangs from, containing all the wires associated with that spot? Or, should I not only have a junction box that the light hangs from, but a nearby junction box to handle all the splicing, and only having the cable that is going to actually connect to the light in the junction box that the light hangs from? The first way uses less junction boxes, but the second way could be less confusing for a future person to look at from underneath the attic. Basically, which of these images am I doing?
----------------------------------------------------------- (or) -----------------------------------------------------------

Question 3 - Are these two images that I made correct? For example, if using just one junction box at each light, am I having 4 wire nuts in each junction box? A hot wire nut, combining the incoming black, the switch black, and the outgoing black (if there's a box behind this one.) A neutral wire nut, combining the incoming white, the light's white, and the outgoing white (if there's a box behind this one.) A ground wire nut, combining the junction box's grounding wire, incoming bare copper, the light's bare copper, the switch bare copper, and the outgoing bare copper (if there's a box behind this one.) And, a second hot wire nut, combining the switch white remarked black and the light's black?

Question 4 - Do they make a junction box that is permanently open on one side (the side the light's on) and accessible on the other by removing a screwed on plate? It would be physically much easier for me to be able to access a light's junction box from the attic as well as from underneath.

Question 5 - I'm pretty sure about this, but want to make sure. I'm doing two lighting circuits. (So, if one breaker trips, there's still some light.) It's OK to run only one cable for each circuit up to the first junction box in the attic for that circuit, and chain them from there going forward, right? Just want to make sure because right now, each light has it's own cable coming up from down below. But those run past the light switch first, so I'm guessing it was easier to do it that way as new work. Fishing all those spots would be a nightmare, so I'm getting to the attic in one spot, and just coming down for the light switches.

Thank you all SO MUCH!

kbsparky 12-02-2011 03:24 AM

The problem here is when you wire up those switch legs, the white wire (which has been re-identified) should be connected to the black hot lines. If you have a copy of the 2011 NEC, your reference section is 200.7(C)(1):


...If used for single-pole, 3-way or 4-way switch loops, the reidentified conductor with white ... insulation ... shall be used only for the supply to the switch, but not as a return conductor ...

Older editions of the NEC had that information located in section 200.7(C)(2).

HouseHelper 12-02-2011 08:24 AM

1. What KB says.
2. Mount boxes to the rafters or other supports keep the junction boxes accessible after the insulation is installed.
3. Go junction box to ceiling light box. You can use a large J box and smaller ceiling box, and problems are easier to find later.
4. Use a fan rated box in any bedrooms with 14/3 to the switch for separate control of fan and light.
5. Use arc fault breakers as required by your local code authority.

darlingm 12-02-2011 12:25 PM

kbsparky - Thanks for pointing that out! I do have the 2011 NEC, and looked at and around that section. I'll make sure to have the re-identified white wire supplying the switch.

HouseHelper - Thanks for all your comments! Would you recommend having all of the cables above where the insulation will be, or would you run it along the floor, and only up and down where appropriate to get to the junction box? Thanks for mentioning the 14/3. There aren't any fans, but since I'm redoing it anyway, I'll run 14/3 from the switch box to the light box, so it's there for the future.

darlingm 12-02-2011 05:21 PM

Someone pointed out to me elsewhere that current code requires a neutral at switches.

I'm going to go with your idea, HouseHelper, and use fan-rated boxes. Even though I have single switches and just lights now, I'd like to run the correct cable that would allow a future installation of a light/fan combo unit, having it be possible for that to be controlled either by a single or dual switches. If I want to do all this and have a neutral accessible at the switch to comply with code, is it 12/2/2 with ground cable that I should be running?

Making sure to follow code and have the functionality that I want, is this the correct way to go?

darlingm 12-02-2011 05:58 PM

Hmm. Looks like the neutral at a switch requirement is in NEC 2011, and Michigan (my state) is still on NEC 2008. Am I correct that the neutral is only being added to the requirements for smart switches? Wonder if it's worth running 12/2/2 over 12/3. Unsure how smart switches will be in the future, they haven't peaked my interest yet. My local prices are:

$67 - 250' of 12/2 w/ ground
$120 - 250' of 12/3 w/ ground
$233 - 250' of 12/2/2 w/ ground

.. So it's a $133 difference to bring the neutral to the switches.

darlingm 12-02-2011 06:22 PM

Sorry to everyone for making so many replies today going in different directions. :eek: I've learned a lot today, thought through a lot, and changed my mind a lot.

I'd love to run smart switch ready cables, or at least cables that can also run a fan. But, cost is a real problem now.

I may regret it later, but we are going to treat this as a "make the house safer" project rather than an add functionality for something we may or may not ever use (fans, smart switches.)

I'm just going to run 12/2 w ground everywhere, instead of 12/3 or 12/2/2. The few hundred dollars difference is a tremendous amount to us right now.

kbsparky 12-02-2011 07:07 PM

You are NOT required to install a neutral wire unless you actually need it. The requirement in the 2011 NEC only applies to areas that will be later inaccessible.

Since you are "fishing" your lines in now, there is nothing to say that you can't "fish" in another wire later, if and when you need it. The Code recognizes this as the mandate only applies to switches which would be impossible to fish additional wires at a later time.

IF you really wanted to make things easy for future installation of another conductor, then I'd suggest that you install some ENT (flexible conduit) and leave a string in place to add the neutral wire later. You could use type THHN wires, and install the correct colors the first time around.

The Code also recognizes this as satisfying the requirement.

PS: I would use 14/4 for such an installation, much cheaper than the 12/2/2.

darlingm 12-03-2011 03:00 AM

Thanks for everyone's responses! One more question about this post, sorry guys, LOL!

I'll be putting the junction boxes high enough that insulation won't cover them.

Where I could run a particular cable along the attic "floor" or "ceiling", which should be my preference? Some say to run the cable along the floor, so the electrical is insulated against the summer heat. (I live in Michigan - not too hot, but we do sometimes hit 100F.) Others say to run the cable along the ceiling, so if the cable heats up, it can dissipate easier than if it was buried in insulation. I will be using a combination arc fault GFCI breaker, if that makes much of a difference.

kbsparky 12-03-2011 04:39 AM

Doesn't matter which. The cable is rated for 90 degrees ambient temperature. That's 194 F. Way hotter than it will ever get up there.

darlingm 12-04-2011 01:51 AM

Awesome. Thanks! I'm leaning toward having them high up. Just seems cleaner to me to not have them buried, without there being a clear reason to go one way or the other.

Want to double check the minimum distance that I can have between the underside of the roof deck and the electrical cable. Believe it's 1.5" (without getting into metal plates.) In some areas, I might attach to the bottom of a 2x4 running along the roof deck. I can't remember if they cheated both dimensions of the 2x4, but whether it's actually 1.5x3.5 or 1.5x4, that would give me a minimum clearance of 3.5". Just want to make sure there's no other special consideration needing to be given with a roof deck. :)

darlingm 12-04-2011 03:16 PM

In case anyone runs by this post in the future, I wanted to reply that I'm seeing numerous sources all say that FHA guidelines are that everything should be at least 3" away from the roof deck. Didn't find something saying that on or, but I'm comfortable believing that's the rule since that's what everyone's saying.

mnp13 12-04-2011 11:17 PM

Why are you running 12/2 and not 14/2? You'll save yourself a TON of money. I'm just finishing my attic/second floor rewire and before I'm done will have opened my fourth 250 foot package of 14/2 Romex. I had no idea I was going to go through that much, but even with the end in sight, I know there's another purchase coming soon.

All of my switches are done with switch loops, because that's how they were already there and I could just pull the new wire using the old. It saves a lot of wire as well, since you're not dropping a wire to the switch from the attic, then dropping a second wire next to it to go up to the fixture.

Mine go: wire from switch to junction box, wire from fixture to junction box, power wire to junction box.

I put almost all of my junction boxes in the rafters, not along the floor because I didn't want them buried in insulation. If I decide to run a new wire for some reason, I can just poke up through and not have to dig through everything looking for the boxes.

Also, remember that if you are running the cable over any place that can be walked on, you have to either drill through every board (yuk!) or you can do the easy "cheat" and attach a 2x4 across the top and attach the cable to the side of it. That prevents the cable from being stepped on, and saves you the headache of drilling through all your joists. I don't know if the "ceiling rule" counts in attics or not, but in the basement, you have to do the same thing so that nothing can be hung from cables. (I don't know why anyone would do that in the first place, but evidently code has to assume everyone is an idiot...)

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