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Old 10-22-2013, 11:42 PM   #1
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Installing new sub panel in the attic


This is my first post/topic. A big THANK YOU to everyone who keeps this forum going, as it has already proven extremely helpful to me in putting together my rewiring plans.

Looking for some advice here; all the existing rewiring in my 90 yr old home is the original K&T, so I wish to upgrade all of it. As a part of this (massive!) project, I have decided to install a sub panel in the attic and drop all new circuits to the 2nd floor down from there. I will try to provide as much necessary information as possible.

Before anyone warns me: I realize there are possible code issues for this sub panel location. However, this attic has a permanent stairway and is easily accessed via a door on the 2nd floor; you literally open the door and go up 5 steps to the location I plan to install the sub panel. There is plenty of working space on the right hand wall of the landing, so I believe I am good as far as NEC service box requirements (my locality uses the NEC 2011, no addendums that I am aware of). The panel will be on an exterior wall.

The attic sub panel will be 60 amps, run off of my existing 100 amp main service panel in the basement. We have gas heat and water heater, so 100 amps is plenty for us at the moment. This 60 amp panel will have a 20 amp bathroom circuit, and enough circuits for receptacles in 3 bedrooms and all the lighting. I anticipate that two additional 20 amp circuits and one or two 15 amp circuits will be sufficient for all of this.

As feeder to the panel, I plan to use maximum 40 feet of either:

A. 6/3 romex with ground
B. three #6 THHN wires (black, black, white, and one #8 green ground) in some kind of conduit.. probably PVC...?

I haven't decided which, and this brings me to the part I haven't quite figured out yet: according to the NEC, where and how I am allowed to run these two different configurations of cable?

NM/Romex

I have read some things that seem to say that for Romex/NM cable I would have to open up the walls (and plaster walls at that... no fun!) and fasten the cable every 4 feet to wall studs. But somewhere else, I read where you are allowed to fish #6 cable vertically and unsupported up to a maximum of 100 feet (would only be about 30 feet vertical for this project), as long as it is secured at the top of the run. Can I just do this between wall studs and call it good with no protection or fasteners??? Which is correct? The entire run of vertical cable would be behind finished walls.

THHN

Somewhere else I read that you are able to run THHN in conduit unsupported (as long as you have a bushing or something at the top). This makes sense to me, but does the conduit itself need to be supported? Can I have conduit connections or does it need to be continuous? And how would I go about running conduit inside of finished walls in the first place...? I also plan to have insulation blown into the walls after I am finished; is this a problem (heat)?

My preferred solution would be to figure out a way to drop conduit from the attic all the way to the basement, for several reasons:

1. from what I understand, THHN would allow me to use the 90 degree ampacity column, and therefore a bigger breaker in the basement (though the 60 degree column would be ok; the attic gets hot, but not more than 130F)
2. if i install conduit, at some point way down the road either me or a future owner is likely to find it very convenient!
3. the THHN is a little bit cheaper and easier to work with

What does everyone think about my plans as presented here thus far? Any red flags? I of course plan to have it all permitted and inspected, and I plan to call the inspection department ahead of time to make sure all my plans will fly.

The main thing I'm looking for here is input on how to run the feeder cable through the walls. Most everything else I feel somewhat confident about.

Thanks in advance. Sorry for the length, just trying to be thorough .

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Old 10-23-2013, 01:36 AM   #2
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Installing new sub panel in the attic


Neither the cable or conduit is required to be supported behind fished walls.

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Old 10-23-2013, 01:43 AM   #3
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Installing new sub panel in the attic


As long as the next home owner knows to go up there for those circuits in that panel (ie place a tag inside the main panel, telling them the 60 amp or 100 amp breaker at whatever panel location in it, feeds a sub-panel in the attic).

I know that it would be easier to just pull the Bath if there is one, the lighting for the bath & upstairs and a couple of rooms and the hallway into the subpanel up in the attic, but you are only talking about maybe four maybe five circuits, with one of them being a 20 amp, if there is a bath up there, hvac if you are placing up there, or the bath without a Jacuzzi tub with heater, per say; I would just pull it all down to the main panel if you have a nice chase to pull those four maybe five runs of romex down there.

Now if you were doing ten, maybe twenty circuits upstairs, then yes I would do a sub-panel, otherwise, just pull everything into the main panel. While you are at it though, I would pull Cat-5e or Cat-6 for Ethernet & phones, and RG-6 for Antenna, Satellite, CATV also, while you are doing it. Figure two runs of Ethernet, Coax per jack, maybe two jacks per room. Also figure possible Network WiFi for any technology like Network connected Thermostats & Smoke/Heat/CO detectors also.

As for opening up the walls, yes it makes it easier if you have a lot of pulls, but if you are able to just use a flexbit and fish sticks to pull the lines down from the attic, vs across the wall, it does make it easier. Either way, as long as you are not tearing all of that old Plaster & Lathe down, to install insulation, which should be done after fixing any rotted wood, and the new wiring, and any plumbing issues, you do not have to secure inside the wall space.

BTW, double check with your local, to see what the requirements are for AFCI breakers in bedrooms and living spaces.

Before you commit yourself to this, make sure you have all of your ducks in a row. That means getting some "Smart Boxes" for locations that you can attach the retro box to a stud, if you are placing new outlet locations, or for low voltage, along with enough outlets and switches. Also look at just purchasing 1000' rolls of 12/2, 14/2, 500 foot rolls of 12/3 & 14/3.

Any networking stuff for tv, try to keep it simple if you can. You can use ceiling mounted Access Points that work with Power Over Ethernet, so that you do not have to wire a outlet for power to those locations, but you need to have at least a switch on the second floor if you plan on adding that to your list.

I just wanted to throw the networking & coax stuff out there, because people forget about that part, when they do rewiring, and while they have the walls open, for putting in the wiring and insulation, you might as well knock it out at the same time, instead of having to do it later on down the road, and kicking yourself in the pants for not doing it, when you had the walls open.
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Old 10-23-2013, 08:07 AM   #4
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Installing new sub panel in the attic


Extremely helpful, both of you. Thanks so much.

Gregz:

The other reason I have decided to go the sub panel route which I neglected to mention before is voltage drop. Because of the main panel location, if I wire them all the way from the basement, the one way distance for some of these upstairs receptacles is going to approach 50 feet, perhaps even more. According to the reference I have (Wiring Simplified, 43rd ed.) the voltage drop under heavy loading (I have a wife and a daughter; I figure 15 amps, maybe 20, for each ) could become a problem at these distances.

Plus, while I only plan to have 4 or 5 circuits now, who knows what the future holds? We might decide to finish the attic at some point, or expand the 2nd floor onto the existing 1st floor addition.

Good thinking on all the other wiring. I've never looked into power over ethernet; what would I use that for? Also: is it OK to run Cat5/6 in the same cavity as power cable or does it need to be separated?
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Old 10-23-2013, 08:15 AM   #5
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Installing new sub panel in the attic


I agree with idea if less than five circuits don't do a sub panel. Do home runs back to main panel. If more or you want future expandability then maybe an attic sub panel.

Another option is a larger junction box in the attic. Say a 6" x 6" x 6" box. I'd then go NM/Romex from the jbox to the various wall and ceiling locations. Feed the junction box via conduit and THHN to main panel then you can pull wires for the circuits you plan today but still have ability to pull more wires in the conduit down the road. Gives you the future proofing you may want but avoid a second panel and the confusion with that. I'd tend to go with 1" conduit since wire fill will likely be limited by ampacity reasons and not volume fill limitations.
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Old 10-23-2013, 08:20 AM   #6
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Installing new sub panel in the attic


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I'd tend to go with 1" conduit since wire fill will likely be limited by ampacity reasons and not volume fill limitations.
Thanks for the advice on that; I had forgotten to even ask what size to use. I know there are tables in the NEC, but I was already planning to go bigger for future expandability.

Any thoughts on how to run the conduit into the wall? I have no idea what type of construction I have, or if there are going to be sill plates in the way between floors, or other issues.... how do I get three 10' lengths of conduit into my wall??? Easier to drop down from attic or shove it up from the basement..?
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Old 10-23-2013, 01:13 PM   #7
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Installing new sub panel in the attic


How old is your current 100 amp main panel? Can you post a pic of the sticker?
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Old 10-23-2013, 01:16 PM   #8
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Installing new sub panel in the attic


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How old is your current 100 amp main panel? Can you post a pic of the sticker?
It was installed in 1996; everything from the main to the pole was redone at that point (I looked up the permits). I'll try to remember to get a picture when I get home. Why?
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Old 10-23-2013, 01:23 PM   #9
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Installing new sub panel in the attic


I am about to embark on the exact same - replacing service and replacing hodgepodge of wiring from just about every era from K&T to now in an 87 year old house. I too am planning to put a subpanel in my attic. A few points that drove me to a number of cable runs that made a subpanel make sense to me:
  1. Lights and outlets for existing finished attic
  2. Planning for dedicated heater/light/exhaust fans in two baths
  3. Plugs in each bath on their own circuits
  4. All plugs and lights on separate circuits
  5. Hall and stair lights for three way switches
  6. Voltage drop (even though lots of pros say don't worry about it in residential)
  7. Interconnected smoke alarm circuit
  8. Derating required if running multiple cables together.
You could probably get up from the basement in the walls, but you are going to have come down from the top to get to overhead lights, exhaust fans, and probably smoke alarms.

Also, wherever possible, my plan is to drop down from the attic to the baseboard, and then run wires through the studs behind the baseboard from outlet to outlet. This will avoid having to fish through blown in attic insulation on external walls.
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Old 10-23-2013, 01:24 PM   #10
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Installing new sub panel in the attic


There should be a maximum branch breaker size and the temperature listing. Even though thnn is rated for 90, your panel is probably not and would limit you to 75 or even 60.
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Old 10-23-2013, 01:30 PM   #11
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Even though thnn is rated for 90, your panel is probably not and would limit you to 75 or even 60.
Ok.... but that panel is not in the attic with the high temps, it is in the basement. The attic will have a new panel.

I guess I don't understand why the temperature rating of the basement panel and the breaker is relevant..? Unless you are saying the whole system from pole to receptacle has to have 90 degree rating in order to use that ampacity? Is that it?

If so, I guess I'll just be stuck using a 60 amp breaker with the THHN. Oh well; that's probably plenty for three bedrooms, a bath, and an unfinished attic, anyway.
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Old 10-23-2013, 01:43 PM   #12
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Installing new sub panel in the attic


You are not going to have that much voltage drop, wiring from a main panel to the second floor and attic, as is done with 99.99% of homes that style. Just make it easier on yourself, and pull all runs from the basement to where they need to go.

Now of course if you are just using one 1000' roll of Romex for 14/2 or 12/2, yes you are going to have to pull multiple times, but that is how it is done with licensed sparky's.
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Old 10-23-2013, 01:55 PM   #13
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Installing new sub panel in the attic


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Ok.... but that panel is not in the attic with the high temps, it is in the basement. The attic will have a new panel.

I guess I don't understand why the temperature rating of the basement panel and the breaker is relevant..? Unless you are saying the whole system from pole to receptacle has to have 90 degree rating in order to use that ampacity? Is that it?

If so, I guess I'll just be stuck using a 60 amp breaker with the THHN. Oh well; that's probably plenty for three bedrooms, a bath, and an unfinished attic, anyway.
100 amps should be ample power for a non-electric house. I really don't know how to word this, but you can diversify your loads too much, not trip a branch breaker, but trip your main.

Your current main would have a maximum branch breaker (amperage) size listed.
Your main and proposed sub panel will have to be rated for 90 terminations to use the 90 ampacity.
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Old 10-23-2013, 01:56 PM   #14
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Installing new sub panel in the attic


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Originally Posted by gregzoll View Post
You are not going to have that much voltage drop, wiring from a main panel to the second floor and attic, as is done with 99.99% of homes that style. Just make it easier on yourself, and pull all runs from the basement to where they need to go.

Now of course if you are just using one 1000' roll of Romex for 14/2 or 12/2, yes you are going to have to pull multiple times, but that is how it is done with licensed sparky's.
I'm with Greg on this one don't worry about the drop.
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Old 10-23-2013, 02:52 PM   #15
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Your main and proposed sub panel will have to be rated for 90 terminations to use the 90 ampacity.
Ok I guess that makes sense. Is a 1996 era panel likely to have that rating or could it easily go either way? I guess I'll just check it when I get home.

I will also check on the maximum branch circuit. Didn't know that could be an issue.

Gregz and 47:

Forgive me, but I still don't understand why I should do home runs. What is the advantage? From what I understand, tripping the main breaker would only happen if the capacity of that panel is exceeded (I know I'm simplifying). Isn't the same amount of current being pulled onto the main rails via the main breaker no matter how the current is distributed? Doesn't 30 amps of sustained current through three circuits look the same to the main breaker as 30 amps of sustained current through one circuit?

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