I’m new to this forum stuff, so I’ll say thanks ahead of time
for suggestions. I’m currently remodeling my bathroom on the
second floor. One of the new items being added is an electrially
heated tile floor. The company suggests that the floor heater has its own separate 15amp circuit. I have been able to trace the conduit down to the basement from the current line run. My question,
can I run two sets of 14 awg wire through the same piece of conduit?
this would obviously save me from putting in a second run.
Thanks,
Johh Brunke
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Assuming 1/2" conduit ... no problem for running 2 sets of 15 Amp wires. Depending on how many bends in the run it could be difficult to add 2 wires to an existing run. Depending on the length of the run, it may be best to use the existing wires to pull in 4 new wires. 15 amps is pretty small for most heaters. Make sure the heaters only need a 15 amp circuit.
Ahh.... conduit, I love conduit. Yes by all means do it. I wish more homes were equipped with it. You can run up to at least ten wires (14 gauge) in a half inch conduit I believe. Don't quote me, The number escapes me at the moment. And I agree that a 15 amp circuit seems small for a heater. But not impossible. Good luck
Based on Table C-1 in the '96 Code, it's 12 conductors [40% fill].
But I wouldn't press it. If you're gonna have that many wires, use a larger conduit. And don't forget the lube and use my patent pending super bend where-ever you can.
-Peter
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Edited 10/6/2002 10:37:38 PM ET by PM22
"Based on Table C-1 in the '96 Code, it's 12 conductors [40% fill]."
But, but, but.
There are a couple of things missing here. The type of conduit and the type of wire. That can drastically change the numbers.
Most likely the new wiring will be THHN, but no telling what the existing wiring is.
Also this requires derating. With 4-6 current carrying conductors the amp has to be derated to 80%. As #14 actually has an ampacity rate of 20 amps then when derated it will be 16 amps which is OK as this is an 15 amp circuit.
If you get up to the 12 "allowed" then you have to derate to 50% and thus need to up size the wire.
I'll take your word for it. That's why I don't trust the code. The table "C-1" says 12 conductors [THHN] but doesn't say anything about derating.
If you derate to 50%, then the #14s are worthless. Does the Code lie?
-Peter
Introducing a new notion.
No, as far as I know, the code doesn't lie. But it must be taken as a whole. Off hand there is only one article that will neatly give you the whole truth that is to be applied in all places and at all times: "Electrical equipment shall be installed in a neat and workmanlike manner."- NEC. Everything else is provisional and dependent on other considerations or conditions.
The number of current carrying conductors in a conduit, the ambient temperature surrounding the conduit, the type of conductor material (Typically copper or aluminum but nickel-clad copper, silver and many other materials are more rarely seen.), the temperature rating of the insulation all go into a proper design of a circuit. Notice that it is the insulation not usually the conductor itself that limits the amperage.
While over 90% of the residential installations and situations are effectively covered by a small portion of the code there are fine points and nuances that must be observed. These seemingly insignificant details can make the difference between "an installation essentially free from hazard" and a handy way to get to know the local fire department.
The code does not lie.
But you have to understand it. Look at the title of the charts. They are for volumentric fill. They just take care of the computations from another section of the code that indicate what percentage of the conduit can be filled with wire. And the tables in appendix C or limited to cases where you have all the same size and type of wire. Otherwise you need to go to the formulas (or assume worse case and use the biggest wire).
The purpose of volumentric fill percentage is to indicate show that the wires can be pulled without damaging the wire.
So that is only one part of the "system".
Section 310 is conductors or wiring and it talks about capacity rating for the wiring. In that you have the different tables that give the "ideal" capacity of wiring depending on the type of wire, insulation, and size. You also have the tables and forumlas for derating the capacity.
The whole sizing is based on how much heat is generated in the wire and how much heat the insultaion can stand. So there is derating if the wires are in hot areas and/or if you have bundles of wires (as in a conduit) so that the heat can't disipate.
Bill,
Thanks for all your input. Can you translate some of your
discussion for me. I have found an entry point to the bathroom
through a 15 foot run of standard 1/2 inch metal conduit.
It currently has three 14 AWG wires running through it.
Now I want to run 2 additional 14 AWG wires through that run.
It sounds like I can do that, but I was confused about the
temperature question. Part of that run will go through the
attic area. Are you concerned about actual air temperature
or the heat created by those wires in the conduit.
By the way the house is 8 years old. I'm not sure if that
helps answer the wire insulating question. Again, thanks for
the info.
John
You should be OK.
You will probably be pulling THHN and that has an ampacity of 25 amps. Even after derating it is still has more than 15 amp capacity.
Barring any unusual situations I agree with Bill Hartman. If the conduit ran directly behind a radiator or installed space heater temperature derate would be a consideration. With only 5 wires, only four are current carrying ( 2 hots and 2 neutrals ) conduit fill isn't something you need worry about.
The heater is from a company called Suntouch.
Fortunately for me the bathroom does not have
a huge amount of floor space. The 15 amp should
be more than enough. Thanks for your input.
Yea, conduit is pretty cool.
John
A point missing is it is improper to pull new conductors into conduit where conductors already exist. You risk damaging the existing conductors. As John pointed in the second post, Use the existing conductors to pull all new conductors for the new and existing circuits.
Alright, you have certainly answered my questions.
I'll definitely pull new wires through for all the existing
wires also.
thanks.