12-2 and 12-3 through EMT

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Old 01-15-08, 09:34 PM
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12-2 and 12-3 through EMT

I have a very short header over all of my doorways in the house. To get my circuits across these openings, I am thinking that I will use EMT conduit and run my romex through to the other side of the doorway (Because of the house design, I cannot run wiring into the attic). I would like to run a line of 12-2 and 12-3 through the conduit. I have tested putting both through and they both fit with much room to spare. Does anyone see a problem with such a configuration? Would that pass a building inspection?

Thanks for your guidance on this.

Matt
 
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Old 01-16-08, 04:58 AM
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You can run NM in raceways (including conduit) as long as no portion of the run is in a wet location, this is specifically allowed in NEC 334.15(c), search for 334.30 then click on "Type" to the right here:

http://www.neccode.com/videographics.php

The ampacity of the result is calculated per NEC 310.15.
 
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Old 01-16-08, 06:54 AM
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Two cables through EMT

Thanks Michael. Do you see any problem with having two cables in the 1/2" conduit as long as they are loose fitting. I guess I was wondering about hear buildup. These are just 20amp general purpose circuits.

Also, this is on the other side (bedroom side) of a shower wall. The opposite side of a shower wall is not going to be wet, at least I hope not.

Thnanks.
 
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Old 01-16-08, 07:48 AM
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From an ampacity ("current carrying") standpoint you are OK.

However:

1) One thing I don't know is if these two cables would exceed the physical ("wire fill") capacity of a 1/2" conduit. Perhaps someone else here knows the answer.

2) You are left with the problem of protecting the MN from abrasion where it enters and exits the conduit (this is not a problem where it enters a box through a conduit fitting). A municipal inspector would probably require a busing or other protection there.

3) I notice you are running a 12 AWG 3 conductor cable. If this will be used as a multiwire circuit made SURE that the hot (ungrounded) conductors are on opposite phases at the originating panel. If you are not SURE you understand what this means, and why and how this must be done, IMO you need to hire an electrician to wire this circuit for you. See for example:


http://www.mikeholt.com/mojonewsarch...s~20020218.htm
 
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Old 01-16-08, 08:11 AM
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Questions Raised

Thanks Michael. I appreciate you answering my questions.

1) One thing I don't know is if these two cables would exceed the physical ("wire fill") capacity of a 1/2" conduit. Perhaps someone else here knows the answer.
Do you mean the physical space of the conduit? I have fed two cables through with no problem, I could fit one more if I tried.

2) You are left with the problem of protecting the MN from abrasion where it enters and exits the conduit (this is not a problem where it enters a box through a conduit fitting). A municipal inspector would probably require a busing or other protection there.
I had planned on putting some type of fitting on the ends of the conduit. Is that what you are suggesting?

The 12-3 wire is only to operate a 3-way switch light system. How would I determine the phase if I did want to use the second wire as hot coming from the panel. Use the diagram on the panel?

Also, is there a problem with including a bedroom light with my bathroom light circuit? Same with a general recepticale in a shared bedroom wall on my bathroom GFCI circuit?

Thanks again!
 
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Old 01-16-08, 08:31 AM
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> Do you mean the physical space of the conduit? I have fed two cables through with no problem, I could fit one more if I tried.

The number of wires allowed in a conduit (raceway) by the NEC is considerably less than than the number that will "fit" in it - I have the tables for individual conductors, but not for NM cables.

> I had planned on putting some type of fitting on the ends of the conduit. Is that what you are suggesting?

Yes. What's acceptable will depend on the local inspector.

>The 12-3 wire is only to operate a 3-way switch light system. How would I determine the phase if I did want to use the second wire as hot coming from the panel. Use the diagram on the panel?

This is relevant only on a "multiwire" circuit where two "hot" (ungrounded) conductors are sharing a single "neutral" (that's he usual but not in this case technically correct term) conductor. Not relevant if this is a circuit for a "3 way" light switch.

> Also, is there a problem with including a bedroom light with my bathroom light circuit?

A bathroom can share a lighting circuit (not powered from the bathroom receptacle circuit) with another area.

> Same with a general receptacle in a shared bedroom wall on my bathroom GFCI circuit?

A bathroom outlet circuit can power other bathroom outlets - nothing else.

-----------

If you need to ask these questions there is a good chance there is something else you are overlooking, my suggestion is to get a copy of "Wiring Simplified":

http://www.amazon.com/Wiring-Simplif...0497171&sr=8-1

or similar book and study it carefully before proceeding.
 
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Old 01-16-08, 08:51 AM
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Wiring Simplified

I ordered the book.

I have a few of them. I have picked up a number of rules i.e. bath lights and receps on different circuits. 3-way switches etc. I am just trying to get it right so the inspector does not have to come back. The books I have, I can only get so much out of until I actually start wiring things up. Hopefully the book you suggested will assist even more. Will this book give me a laundry list for say "bathroom wiring" or am I going to have to memorize the book from end to end to keep from coming back to the forum?

Thanks.
 
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Old 01-16-08, 09:17 AM
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Originally Posted by matman View Post
Will this book give me a laundry list for say "bathroom wiring" or am I going to have to memorize the book from end to end to keep from coming back to the forum?
This is useful for "quick reference":

http://www.amazon.com/Code-Check-Ele...0499879&sr=1-1

Here are some residential electrical inspection checklists, also check if your local building department has one as a handout:

http://www.sanjoseca.gov/building/pd...s/rqmLight.pdf
http://www.electricity.state.mn.us/E..._checklist.pdf
http://www.nachi.org/forum/attachmen...3&d=1136035954
 
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Old 01-16-08, 09:35 AM
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Good stuff

Thanks Michael. That is all really good stuff. It will help out tremendously. Next time you hear back from me, it will be a really difficult question.

BTW, did you have any ideas on the "wire fill" capacity of the EMT?

Thanks.
 
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Old 01-16-08, 09:46 AM
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Originally Posted by matman View Post
BTW, did you have any ideas on the "wire fill" capacity of the EMT?Thanks.
The NEC limits three or more conductors to 40% of a conduit's cross-sectional area, and I would assume that would also apply to cables - perhaps some electrical guru will be along to confirm that. As a home inspector my aim is to know enough to identify a possible problem, in a case like this I then defer verification and correction if required to a "qualified electrician".
 
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Old 01-16-08, 10:37 AM
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When a short sleeve of conduit is used for protection over a cable (as in your case), the fill limit is the number of cables which can be installed without damaging the cable. So, if the cables fit loosely and the end of the conduit is open such that air can flow in, then I don't believe there is any problem.

The 40% rule does apply to cables in conduits, but only when the conduit is used as a raceway and not as a short piece of protection. For future reference, when computing the cross-sectional area of a cable, you measure the widest dimension of the cable and compute the area as if the cable was round. This requirement makes conduit fill go up really fast when looking at 12/2 romex which is a flat oval of about 5/8" x 1/4". With the 5/8" dimension it has a fill factor similar to 200A service entrance conductors.
 
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Old 01-16-08, 10:55 AM
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let me add to Ibrooks's comment.,

with the EMT or any other conduit if you are more than 24 inches [ 60 CM ] the derating effect do apply on this but your case it may squeak by but as Ibrooks point out all the romax are being sized by the widest part of the cable itself that how we count the fill size and the NEC do have a chart somewhere but you only have one power cable and one cable is being used by 3 way switch it can be ok but please do not add anymore in there it is allready crowed by the term of space.

Merci, Marc
 
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Old 01-16-08, 11:04 AM
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Originally Posted by ibpooks View Post
For future reference, when computing the cross-sectional area of a cable, you measure the widest dimension of the cable and compute the area as if the cable was round. This requirement makes conduit fill go up really fast when looking at 12/2 romex which is a flat oval of about 5/8" x 1/4". With the 5/8" dimension it has a fill factor similar to 200A service entrance conductors.
Do you happen to know the NEC section for that? I'd like to add it to my notes.

Also, what does the NEC have to say about the protection of NM cable at entry and exit to the conduit?
 
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Old 01-16-08, 11:17 AM
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Originally Posted by Michael Thomas View Post
Do you happen to know the NEC section for that? I'd like to add it to my notes.

Also, what does the NEC have to say about the protection of NM cable at entry and exit to the conduit?
ATM I don't have the codebook with me right now but it did expain in one section.

for the protection of NM cable at entry and exit of conduit itself there is a device for this either using a bushing sleeve that slipped on the EMT or use EMT/ Romax adapator one of the two will prevent chaffing the romax cable.

Merci, Marc
 
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Old 01-16-08, 12:26 PM
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Romex and EMT

French,

The total span is 80" (had to span door opening and a pocket door false wall).

If I am going to run into problems with NEC it seems like I could use the 12-3 for both and have a smaller net diameter (since the 12-2 is flat and the 12-3 is round).

Is it that the fill cannot exceed 40% of the XSA or that 40% of the XSA must remain?

Thanks!
 
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Old 01-16-08, 12:43 PM
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You could also place a box at each end, and run individual conductors between them. The boxes' cover plates would have to remain accessible, however - you could not for example drywall over them.
 
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Old 01-16-08, 12:52 PM
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Originally Posted by matman View Post
The total span is 80" (had to span door opening and a pocket door false wall).
At 80", you should probably just run two 1/2" EMT conduits side by side with one cable in each, although I doubt the inspector would raise an issue about this because it's not a sealed conduit system.

Is it that the fill cannot exceed 40% of the XSA or that 40% of the XSA must remain?
The XSA of the conductors cannot exceed 40% of the XSA of the interior diameter of the pipe. So, 60% of the conduit interior must be airspace. If it's only one cable in the conduit you can have 53% fill, 47% airspace.
 
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Old 01-16-08, 01:04 PM
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Originally Posted by Michael Thomas View Post
Do you happen to know the NEC section for that? I'd like to add it to my notes.
Chapter 9, Table 1, Note 9: A multiconductor cable or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.

But it's also important to look at Note 2: Table 1 applies only to complete conduit or tubing systems and is not intended to apply to sections of conduit or tubing used to protect exposed wiring from physical damage.

Because of this provision, fill doesn't really matter in this case as long as the cable is not damaged by jamming it into a small conduit.
 
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Old 01-16-08, 01:23 PM
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Boxes at each end

Michael has a good suggestion.

Would this fly?

1. Put a box in closet with white cover
2. Run individual conductors (5)
- 1 Hot
- 1 Neutral
- 1 ground
- 1 common (for 3-way switch)
- 1 traveler (for 3-way switch)
3. Box behind wall-mounted TV white cover
4. Supply recep
5. Supply switch
6. Use 12-2 to connect from switch to box 2 traveler and common

Thanks for your suggestions.
 
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Old 01-16-08, 02:33 PM
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12-2 and 12-3 cable protection

Sweet news Ben! There is no maximum length to the provision? It would definatley not be a complete conduit or tubing system. Thanks for your response.

All I need to complete this job is a couple of bushings or NM to EMT adapters.

Thanks for everyone's help on this one!
 
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Old 01-16-08, 04:01 PM
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ibpooks,

Thanks for the code cite.
 
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