conduit/conductor amount

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steve-in-pa

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i am pretty confused with this subject. my plan- to add 4 receptacles in bedroom(2nd floor)all on one circuit.

my plan is is to come up from the basement with 12-2-2 romex, to a junction box on the attic floor. from there, i'd use 1/2inch emt(across attic wood floor) to 4 junction boxes, which would each be located over the bedroom wall below where i'd like to add a receptacle.

the 12-2-2 is going to be "half used.

the 12-2 part will feed the 4 new bedroom receptacles. if i have a tripping breaker(afci) i would use the "other half" of the 12-2-2.

in the 1/2 emt, i'd run thhn #12, with a green,black, and white. all 4 junction boxes/receptacles in paralell.

ques1- do i need to derate for any reason, or can 20amp afci be used?
ques2- if in future i use the 2nd half of the 12-2-2, and run another white and black in the 1/2inch emt, will i have to derate?

i'm running 12-2-2 in case i get stuck in future, and need a dedicated line, for air cond, computer, etc. if i do have to derate, would 3/4emt fix the derate problem?(be able to use 20amp afci? run length is prob 80'total.

I'd use 12-3 to get to the attic, and if a dedicated line was needed, i'd use a green,white,and2 hots, on a double pole breaker, but i'm afraid the afci's might get mixed up electronically, and trip when not supposed to/eratic bahavior. thanks for any help,info,advice.
 
Re: conduit/conductor amount

As for your questions, there should be no reason to derate in any of the cases that you listed.

#12 is good for 30A per the table 310.16 although it is only allowed to be fused at 20A.

You can use the 30a rating for derating purposes as long as your fuse doesnt exceed 20a.

As for the 3/4" conduit, derating is a number of conductor issue, not a conduit size issue.

Hope this helps
 
Re: conduit/conductor amount

thanks for the quick reply.

if i did get "stuck" in the future, and had to add a dedicated line(wiring), in the same emt that would currently be running the 4 bedroom receptacles, would 1/2inch be ok, or should i just stick with 3/4emt?

i have a half inch bender, but i guess a 3/4 could be added to the tool collection.

i guess my main concern is- can a single green, 2 whites, and 2 blacks (all#12thhn) be used in the 1/2inch, at 20amps per circuit.(2circuits)

or i guess i could use the 1/2inch, and if i get stuck, add 3/4 where necessary.

any opinions on multi circuit(12-3) running 2 afci's,ex: inteference,etc? i can't try it out, and then have a problem/tripping/etc, after the wallpaper goes up. :)

thanks for any and all advice. i'm not famaliar with emt/conduit sizing,etc.,,,my father did that part, but now retired and not 100% with his memory.

cheers
 
Re: conduit/conductor amount

Steve, Table 310.16 and the chart below would help you for de-rating and table C.1 in appendix C of the NEC would tell you that you only fit 5 #10's in a 1/2" EMT (THHN)
 
Re: conduit/conductor amount

I have had problems with 2 AFCI's on a 12/3, try to stay with sepate 12/2's
 
Re: conduit/conductor amount

5 #10's? i'd be using #12's.

would the 4 #12's fit in 1/2inch, with a green ground? (at a full 20 amps?)

i gotta get that chart...
 
Re: conduit/conductor amount

Originally posted by steve-in-pa:
5 #10's? i'd be using #12's.

would the 4 #12's fit in 1/2inch, with a green ground? (at a full 20 amps?)

i gotta get that chart...
Click to expand...
:confused:


It's all in your code book.

Roger
 
Re: conduit/conductor amount

Steve...why run conduit at all? Unless your city has a provision for it, it will only take extra time.

Why not just run a few spare 12/2's up to the attic area? They will be there when, and if, you need them. You could also just leave a drag line or two in place.
 
Re: conduit/conductor amount

thanks for the tip. i'm running 12-3 up tha wall to attic, then making split circuits in jb's, then running emt over wood floor, so they can step on it,etc, without damaging wire. conduit will end at a jb, right over receptacle location for bedroom locatiojn below. just worried inspector may say bx and thhn i'm using, with a 90 c rating, will say it needs to be derated to 15amp, or run 10gauge to compensate. may converse with him, as this job is giving mea headache. i see rx run in attics every day, new homes too, but everyone and code book tells me to derate. running #12 throughout. bx up wall, thhn-conduit over floor.
 
Re: conduit/conductor amount

You're running EMT across a wood floor?
eww.gif


There's got to be a better way to get this done!

Edit: Oh, the attic has a floor. I'd use romex the whole way, and either route it away from the floor if possible, or nail down furring strips to protect the romex from foot traffic.

You can't use 12-3 on two AFCI breakers, because the two hots will be sending varying amounts of current back on the neutral that will trip out the GFI function of the breaker. You'd either have to install a $200 2-pole AFCI breaker, or run two individual 12-2 circuits, using two 1-pole ($20) AFCI breakers.

[ May 29, 2005, 10:09 AM: Message edited by: georgestolz ]
 
Re: conduit/conductor amount

One other thing: you're adding time and unnecessary splices in the attic. Just pull your home runs into the attic, and into the first receptacle you're feeding. Loop them just like you would on new construction, only get your length of the "feeding cable", cut it, pull length to your next location, cut it, return to the first hole and fish your two cables down the wall at once.

Putting all those junction boxes in the attic looks bad, takes extra time, and could haunt you if you mess it up.

Sorry for sounding this way, but how long have you been in the business, Steve? :)
 
Re: conduit/conductor amount

If he is in PA, for about 90% of the state, you only need to write on the side of the family mini-van "Elektrikal Kontractor" with a Crayola and you're an electrician.
 
Re: conduit/conductor amount

Originally posted by mdshunk:
If he is in PA, for about 90% of the state, you only need to write on the side of the family mini-van "Elektrikal Kontractor" with a Crayola and you're an electrician.
Click to expand...
We went down to PA from MA for a large project and as soon as someone had a set of lineman's in their hand they where a 'Electrician' :roll: :eek:
 
Re: conduit/conductor amount

so far, i'm surprised at the help i've received here. i thought my plan was simple. up the partition wall with some 12-3mc, make a 3-wire circuit, feeding 2 bedrooms, each bedroom with an afci. as hard as it will be to fish down the walls from the attic, to the receptacles, i figured i'd put a junction box at each location, and pipe box to box, on top of the floor. seems pipe would look alot nicer and neater than wood trapping romex. instead of the hastle of up and down the wall to receptacles, it seemed easier to just fish down, instead of making a month long project of fishing. i think the homeowners can live with the junction boxes sitting on the floor. also, if they decide to add an air cond unit, or clothes iron at one location, i can pipe to that junction box a seperate line. i didnt know 2 afci circuits couldnt be put on a split circuit 12-3, then divided in the attic, to feed the 2 bedrooms. i guess the krayola is rubbing off on my brain, making me do crazy things; neat pipe job, future expansion in case of overload(iron outlet,etc) mc in walls instead of rx,,,, guess the people in MA with the dirty accents also like to do the work in a dirty workmanship way.
 
Re: conduit/conductor amount

Originally posted by steve-in-pa:
so far, i'm surprised at the help i've received here.
Welcome to the home of the honest answer. :)

as hard as it will be to fish down the walls from the attic, to the receptacles, i figured i'd put a junction box at each location, and pipe box to box, on top of the floor.
As hard as it may be, you're going to be doing it anyway, so why not just use the boxes the receptacles are using?

seems pipe would look alot nicer and neater than wood trapping romex.
Do you frequently entertain guests in your attic?
Why do you think romex looks trashy?

instead of the hastle of up and down the wall to receptacles, it seemed easier to just fish down, instead of making a month long project of fishing.
So you're saying that fishing two cables down to that box at the same time will take you a month to accomplish?

also, if they decide to add an air cond unit, or clothes iron at one location, i can pipe to that junction box a seperate line.
You can do the same thing in half the time and just as neatly with romex. You realize, if you use pipe, you'll need to pull the conductors out of the pipe if you want to add conductors to it?
Throw a string down to the basement, use it later.

i didnt know 2 afci circuits couldnt be put on a split circuit 12-3, then divided in the attic, to feed the 2 bedrooms.
Stick around, Steve, you'll learn volumes. :)
Click to expand...
 
Re: conduit/conductor amount

Originally posted by steve-in-pa:
,,,, guess the people in MA with the dirty accents also like to do the work in a dirty workmanship way.
Click to expand...
Wow... Steve must also be a graduate from the Dale Carnegie "How to win freinds and influence people" course.
 
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