# Installing new sub panel in the attic



## Ricyteach (Oct 23, 2013)

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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## rjniles (Feb 5, 2007)

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


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## gregzoll (Dec 25, 2006)

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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## Ricyteach (Oct 23, 2013)

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 :thumbsup 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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## curiousB (Jan 16, 2012)

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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## Ricyteach (Oct 23, 2013)

curiousB said:


> 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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## 47_47 (Sep 11, 2007)

How old is your current 100 amp main panel? Can you post a pic of the sticker?


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## Ricyteach (Oct 23, 2013)

47_47 said:


> 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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## dgfit (Jun 5, 2013)

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:
Lights and outlets for existing finished attic
Planning for dedicated heater/light/exhaust fans in two baths
Plugs in each bath on their own circuits
All plugs and lights on separate circuits
Hall and stair lights for three way switches
Voltage drop (even though lots of pros say don't worry about it in residential)
Interconnected smoke alarm circuit
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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## 47_47 (Sep 11, 2007)

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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## Ricyteach (Oct 23, 2013)

47_47 said:


> 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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## gregzoll (Dec 25, 2006)

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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## 47_47 (Sep 11, 2007)

Ricyteach said:


> 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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## 47_47 (Sep 11, 2007)

gregzoll said:


> 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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## Ricyteach (Oct 23, 2013)

47_47 said:


> 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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## gregzoll (Dec 25, 2006)

It makes it easier to just go to one panel, then having two panels, to hunt for the circuit. As for the thirty amps, whether it is through one panel or two, it is still thirty amps.

Can you post a picture of your current panel with manufacturer & model# info, along with the "Dead Front" pulled off, to show us if there are any current issues that need to be taken care of first (ie not enough space on the current Neutral/Ground bus bars).

If you do not have a copy of the NEC for your code cycle at this time, I would suggest getting one. Also draw out floor plans with current outlet, switch, lighting locations and how the wiring is currently ran from those circuits back to the main.

You may end up finding when you start tearing into this retro-fitted wiring, that there are issues that were left, if it was the previous home owner, or "Handy person" that did the work, not a licensed sparky.

Any info on the current panel, what company did the work previously? Go back to http://www.diychatroom.com/profile.php?do=editprofile under "Additional Information", post your location.

Now back in the day, when they would locate a panel on a second floor, they would just place it in the hallway, so that it was easily accessible, and made it easy so that you would not have to go down three flights of stairs, when you lost the lights or outlets on that upper floor.

How warm does your attic space get also?


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## Ricyteach (Oct 23, 2013)

Sure I'll do that - might be a couple days (I have a 14 hour work day ahead of me tomorrow).


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## gregzoll (Dec 25, 2006)

No biggie. If you are not in a big hurry to do this, just take the time you need, make notes of what was suggested, then go from there. We have all been there, and this is not really one of those things you rush, nor really want to dive into if you live where the temps stay warm all of the time.


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## Ricyteach (Oct 23, 2013)

Here's a few pictures. Didn't have time to take the cover off since I have to get up at 430 tomorrow; I'll do it later. 

https://db.tt/9AhJ6rhe
https://db.tt/onpHOBCL
https://db.tt/DqjWxyb8


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## Ricyteach (Oct 23, 2013)

Ugh I just realized that these pictures are not going to be very helpful. I'll post some better ones tonight (wife is going out of town so it's time to get cray cray).


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## gregzoll (Dec 25, 2006)

Ricyteach said:


> Ugh I just realized that these pictures are not going to be very helpful. I'll post some better ones tonight (wife is going out of town so it's time to get cray cray).


In my household, that means going out to grab some good micro-brew, and watch movies all evening, or heading to the bar to meet up with guys.


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## Ricyteach (Oct 23, 2013)

gregzoll said:


> In my household, that means going out to grab some good micro-brew, and watch movies all evening, or heading to the bar to meet up with guys.


There may be a microbrew involved (this place is on the corner down the street), but the 10 month old is going to put the kibosh on leaving the house. That's ok though- she's pretty cool.


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## gregzoll (Dec 25, 2006)

Ricyteach said:


> There may be a microbrew involved (this place is on the corner down the street), but the 10 month old is going to put the kibosh on leaving the house. That's ok though- she's pretty cool.


My dad's brother lives in Dayton. They have left a couple of times, but always moved back. Also have family in Huber Heights.

Belmont looks like the Friar Tuck that we have here in Springfield, IL. http://www.friartuckonline.com/Index.aspx If I do any work at home, I will usually have a few after, but may have one or two, while sitting down and putting pencil to paper, planning out any electrical work I am going to do, if it is a major job in this place.

I came across some old drawings in the Black & Decker "Complete Guide to Home Wiring". It is the 2005 edition that I got right after we bought this place. I use it mainly for the wiring diagrams, since it is easier to use that, then try and search online for them. Plus the drawings make good book marks.

Some day my kids are going to come across my wiring diagrams and think that dad was too over the wall, when it came to being detail orientated. I came across some of my father's wiring diagrams and schematics. He would use colored pencils and were always very detailed in how they were drawn.


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## Ricyteach (Oct 23, 2013)

Been thinking about you guys' advice a bit more... what would you think about running all of my circuits with THHN up the same length of conduit from the basement to an attic j-box, and then using NM from there to the fixtures? How big would the conduit have to be to run enough 12 and 14 gage wire for... eh... I'd say 5 circuits? And maybe a little bit of room for expansion later? This would accomplish what I'm trying to do (i.e. make it easy to run the wires up to the attic and drop them down from there), while avoiding the hassle (and cost) of a sub panel. 

Or is that exactly what you suggested before? I thought you meant running individual romex home-runs.


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## Ricyteach (Oct 23, 2013)

Here's another idea I just had. Could I save on conduit space by running one larger sized ground wire (instead of multiples) to a separate bus bar in the attic? Is that totally crazy and against code or what? If it isn't against code then I assume the bus bar would have to fit inside the j-box....


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## itsnotrequired (Apr 30, 2010)

assuming 5 circuits (one hot and neutral each) in a single conduit, the conductor allowable ampacity decreases by 50%. for #14 thhn, maximum ampacity would be 10 amp. if the load on that circuit is more than 10 amp, it would need to be increased in awg. similar for the 20amp circuits (if load grater than 15 amp)

and yes, you can run a single equipment grounding conductor for all the circuits, with branches off in the individual conduit runs. you would need a #12 minimum in the common conduit.


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## Ricyteach (Oct 23, 2013)

itsnotrequired said:


> similar for the 20amp circuits (if load grater than 15 amp)


So does this mean that in order to satisfy the 20 amp breaker requirement for a bathroom, I would have to use something bigger than #12 wire in the conduit for that circuit?



itsnotrequired said:


> yes, you can run a single equipment grounding conductor for all the circuits, with branches off in the individual conduit runs. you would need a #12 minimum in the common conduit.


Great! That's even better than I thought. I was thinking ground would need to be a little bigger. 

How can I figure out the conduit size requirement for 5 hot, 5 neutral, and 1 ground, all 12 gage?


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## itsnotrequired (Apr 30, 2010)

Ricyteach said:


> So does this mean that in order to satisfy the 20 amp breaker requirement for a bathroom, I would have to use something bigger than #12 wire in the conduit for that circuit?
> 
> 
> 
> ...


for the bathroom circuit, i don't believe you need to increase the conductor size. the load on the 20a receptacle circuit is already included in the general lighting load so there is no 'minimum ampacity' that the circuit needs to meet. it is a good question though, i'm not totally sure on the answer.

for the conduit, minimum would be 3/4" but you may want to bump up to a 1" conduit, just to make the pull easier.


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## brric (Mar 5, 2010)

itsnotrequired said:


> assuming 5 circuits (one hot and neutral each) in a single conduit, the conductor allowable ampacity decreases by 50%. for #14 thhn, maximum ampacity would be 10 amp. if the load on that circuit is more than 10 amp, it would need to be increased in awg. similar for the 20amp circuits (if load grater than 15 amp)
> 
> and yes, you can run a single equipment grounding conductor for all the circuits, with branches off in the individual conduit runs. you would need a #12 minimum in the common conduit.[/QUOT
> 
> 10 to 20 current carrying conductors are derated at 50%. Derating is done from the 90 degree centigrade column, leaving 12.5 amps for #14 and 15 amps for #12. Use one less neutral and you could derate at 70%, leaving 17.5 and 21 amps respectively. Using the OP's scenario and MWBC's only 3 neutrals would be needed.


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## Ricyteach (Oct 23, 2013)

Are MWBC's as potentially dangerous for the rank armature (such as yours truly) as what I have read? I believe I understand the issues it can create, and I think I understand how to avoid them. I guess I'm just saying I'm just a little bit leary but as always, knowledge is the cure for that right? So lay some knowledge on me.


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## brric (Mar 5, 2010)

Looking back at your photos, how do you expect to get 5 new circuits out of your existing load center?


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## Ricyteach (Oct 23, 2013)

The five circuits will be replacing other existing K&T circuits. This is part of a rewire of the entire house. 

Here are the pictures inside the main which were requested earlier:

https://db.tt/bs1dCGiJ
https://db.tt/G8yHMSQr
https://db.tt/0AWGcrRN


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## Ricyteach (Oct 23, 2013)

Also, the lack of room in the existing main panel is another reason I was thinking about putting that sub panel in the attic. All I would have to do at first is install one new double pole breaker in the main. Would make the wife quite a bit happier if I wouldn't have to shut off the juice for as long that way. 

I am slowly being convinced that the sub panel isn't needed, but it certainly would complicate things as far as keeping power available while I run the circuits. With a sub panel I could just get it all ready to go and then flip on the 60 amp breaker. Done.


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