Flex conduit sizing for 6 #12 cicuits
All,
I’m a weekend warrior tackling bigger jobs as I remodel my 1953 duplex. I’m pulling 6 new circuits to my kitchen. All will be on 15A breakers and I’ll use 12 gauge. I’ll have separate circuits for the 1) accessories, 2) disposal, 3) dishwasher, 4) microwave, 5) toaster, and 6) gas range (the refer is already on a separate circuit). My plan is to run flex conduit from the subpanal, up into the attic, down the inside of the wall that the cabinets are mounted on, exit the wall, and run in flex conduit behind the cabinets to the receptacles. I intend to use 12/2, strip the cover, and pull the whole bundle into ¾â€ flex. Does that work? Do all 18 wires fit? Does Code allow that many wires in a ¾â€ conduit? Is that 6 or 12 conductors?
Thanks for the help!
Warren
“If you have not done it three times, you don’t know how to do it right … but if you’re very clever, the first build can be in your headâ€
— a wise old guy
“If you have not done it three times, you don’t know how to do it right … but if you’re very clever, the first build can be in your headâ€
— a wise old guy
Replies
First thing, you can only put 16 #12's in a flex conduit per Code (and that would be a pretty tough pull to get that many through there.) Also, if you're going to use conduit you may as well buy individual wires instead of going to the hassle of stripping them out of Romex.
Also, the Code requires derating the wire's current carrying capacity when there are three or more current carrying conductors in a single conduit. Assuming the conduit was big enough, using #12's on a 15 amp circuit helps you out some but not much. The amount of derating will depend on the total number of wires.
It may be possible to share some grounds and neutrals to get the wire count down, depending on how you have the breakers installed in the panel.
Is there a reason you have to use conduit? You may be better off running Romex if it's going inside stud walls.
Sorry I can't give you much of an answer, it's pretty difficult to make any definite statements without actually seeing your particular situation.
Stripping the cover off of romex: I have a lot of romex and it turns out to be about 30% cheaper then buying spools of wire.
Derating: I figured on derating the 20A 12G to 75% or 15A to account for putting it in conduit … but I’m not sure that is correct.
And, yes, I thought it would make sense to share some grounds and neutrals to get the number to 16. But honestly, I’m not sure about the Code definition of a “conductor”. I understood the code to be no more then 16 conductors in ¾” … do you count the grounds also?
I’m using conduit in the wall because it access is tight and this will help make the feed through the top plate and to where it exits much easier.
Thanks for you feedback ... it sure helps my thinking!
Warren
Do you live in Chicago?
If not, why not do the whole thing in Romex? Do you really need that many circuits? You can do a multi-wire and end up with a total of nine wire plus one ground.
If you need conduit for protection, you could run one or two 2" conduits up to the attic for protection and run Romex through that. Flex is hard to pull through so I would suggest EMT.
~Peter
I'm in southern California (San Clemente). I think I understand; 3 circuits on one phase, 3 on the other phase, share neutrals for circuits on opposite phases, and use one ground for everything ... that's all legal, right?
Yes, I'm using the conduit for protection. Access is very tight and I can't get EMT in there without opening up the whole wall. So, if I can do it with flex then it's easier and I don't have to add drywall and painting to the work list. I could use 1" conduit if necessary
Warren
Well then, the wall is your protection. You can legally fish the Romex through a finished wall cavity. Get you some Romex clamps listed for 2 cables, attach them about 3 feet up from the end, take off the lock rings and fish them into the panel. 1 3/8" hole should clear the connector.
You seem to understand the multi-wire thing which is good.
Or you could run your flex up to the attic and then transfer to Romex in Junction boxes.
~Peter
Thanks Peter, I appreciate the advice!
Warren
Since this is an upgrade, why don't you bring it up to code and add two 20 amp circuits (non lighting) to the kitchen?
Someone in the future is going to see that #12 wire and think that is what you did, and replace those 15 amp breakers with 20's. Besides, some diposals and microwave can pull close to 15 amp. Nuisance trips of a diposal circuit will drive you or you DW nuts.
May as well get it right when you do it, the first time.
I guess I was getting hung up on protecting half a dozen romex cables snaked down the inside of the wall from an errant picture frame nail at some time in the future. That’s why I wanted it in conduit for that leg of the run from the sub-panal to the kitchen. But, it creates this derating problem, I can’t put the #12’s on 20A breakers, etc. So, should I quit worrying about protecting the romex? Can romex legally exit the interior of the wall behind the cabinets, running through a hole in the drywall, and run horizontally behind cabinets just stapled to the wall (at the studs, of course)? If I drop the whole idea of using the conduit and just pull romex everywhere, then it’s easy to add another 20A small appliance circuit. Now, that’s a buff kitchen!
I should buy the code book.
Well several things. First of all #12 has am ampacity rating of 25 amps nad that is the base current used for derating.If you run multi-wire circuits as you mentioned then you only have the equivalent of 6 current carrying conducting wires.4-6 current carrying conductors require a derating to 80%.So the #12 after derating can carry 20 amps.Now if these where not multiwire circuits then you would have 12 current carrying condutors and that requires a derate to 50%.Also you only need one ground wire.Now for romex. I am not clear on the details, but basically you can run the cable through holes (or parallel on the side of studs) if the edge of the hole (and thus the cable ) is at least 1 1/4" from the surface.Or if it is less than than or installed in groooves or notches or other wise would be within the 1 1/4" of the stud surface then 1/16" steel "nail plate" is needed to protect it.You can also run romex exposed if it "follows the buildigng surfaces" and is not subject to phyiscal damage.Thus you could come of through the wall into a cabinet and running allow the back of the cabinet near the top where no pots and pans which hit it.
Bill gave you the skinny on your derating issue.
If you exit the drywall inside of a cabinet, you should enter a junction box, and from there use flex to each device. Running romex up behind the drawers may be alright, but I would still be concerned about possible damage.
I would assume that you will re-enter the wall at each receptical location, so there is an additional j-box and hole in the cabinet/wall. This would make a much neater and safer run than loose romex running through a bunch of holes and stapled to the back of the cabs. (IMHO)
Figure the house is 52 years old, and you may not be the last owner. Plan your work for future resale, and that inevitable home inspector that is going to point out anything that might be questionable. Trying to explain code compliance to a buyer that has already seen a negative report is futile. You will either change it then or accept a lower price for not thinking about it now.
Dave
If you're running all that many circuits to the same kitchen, another approach would be to run big feeders to a new subpanel in or near the kitchen. That way you don't have derating to mess with, and if you accidentally get the microwave, toaster, and waffle iron on the same circuit, you don't have as far to walk to the breakers. A lot depends on distances and obstacles, and whether you have a nice location for a new subpanel.
-- J.S.