THHN: must it be run in conduit?

flyhopJuly 31, 2013

I have a bunch of 12 AWG red/black/white/green THHN. I am thinking about using it for some indoor wiring projects, and I don't know if I need to run in through plastic/metal conduit or not.

I have a 20 amp feed on 12 AMG Romex terminating in a metal 4 x 4 junction box in the basement. From this, I am planning to feed two ceiling fan/light combinations controlled from 3-way switches on opposite ends of the room. The round-trip circuit from the main panel (200 amp) would be about 100 feet.

The walls are open (panelling removed; drywall going in later) so access is not an issue. My intention is to not have to spend over $100 on 12/3 Romex.

Questions:
1. Can the THHN be run like Romex (through drilled holes between joists, stapled to wall studs)? Or must they be run in conduit?

2. If conduit is a requirement, must I use metal conduit?

3. If I can use plastic conduit, may I tie in plastic conduit to the metal junction box which holds the feed?

Thanks in advance.

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bus_driver

Please enroll in a course in basic electric wiring at your nearest community college. Do nothing else electrical until the course is satisfactorily completed.

    Bookmark   July 31, 2013 at 6:31PM
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flyhop

Why does my question warrant a class as opposed to the other folks you have posted answers to?

I have a reasonably good working and book-based knowledge of basic and advanced electrical wiring. I just don't know all of the rules about what's allowed and what is not. My thread seems like a fairly straightforward question.

    Bookmark   July 31, 2013 at 8:29PM
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petey_racer

NO, you CANNOT run THHN open the same as you would NM cable.

Yes you can use metallic or non-metallic conduit, but it MUST be electrical conduit.

Yes, you can tie PVC conduit into a metallic box.

Personally to do what you propose I think once you are done doing it all in conduit you'll wish you had spent the $100 on romex.

    Bookmark   July 31, 2013 at 9:49PM
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bus_driver

Nothing posted creates any confidence that the person has any knowledge about how to properly install conduit. Or any other electrical materials.

    Bookmark   August 1, 2013 at 7:20AM
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flyhop

You are probably right about running all that conduit. Found 250' for $120, so I bit the bullet.

I'm curious though. What is the reasoning that THHN can't be run without conduit? I'm guessing that expansion/contraction of copper would lead to chaffing. Is there another reason?

Thanks for the input.

    Bookmark   August 1, 2013 at 8:09AM
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flyhop

Bus Driver,
Fair enough.

    Bookmark   August 1, 2013 at 8:56AM
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randy427

In a nutshell, the wire insulation is primarily to resist electrical conduction. The jacket on type NM-B cable, as well as conduit, protects against physical damage to the wire insulation from outside sources. Generally, conduit is used in applications more prone to such damage.
Type UV cable sheathing is resistant to deterioration from exposure to sunlight, and type UF is more resistant to deterioration in wet locations.

    Bookmark   August 1, 2013 at 2:40PM
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inox

I have seen bus_driver discuss controversial subjects in these forums many times. This time, I hope nobody will attempt to undermine his entirely sound position.

    Bookmark   August 1, 2013 at 7:38PM
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flyhop

I was fairly sure my comment "Fair enough" was sufficient to concede his recommendation. I would suggest inox's post be classified as piling on and wholly unnecessary.

I will admit that I don't know much about installing conduit, which is why I asked the question. I came here looking for information...information to fill a gap in my knowledge base. No one asked what my level of experience was, what other information I might have, or bothered to delve any deeper.

It is clear to me that I will have to rely upon other sources for further assistance. Thanks anyway.

    Bookmark   August 1, 2013 at 9:52PM
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Ibewye

Also I'm not sure if PVC is allowed to be run indoors. I cannot verify a code restriction but I remember hearingn about the release of toxic fumes released by PVC during a fire. I understand that during a fire, it may not be the top concern but something to check into.

    Bookmark   August 5, 2013 at 11:38PM
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Ron Natalie

Ton's of things emit toxic fumes during fires. You can't get away from it in modern materials. PVC is fine indoors other than where it's prohibited (such as air ducts).

PVC rigid conduit is allowed for both exposed and concealed use.

It would be better if you actually consulted the code rather than guessing if you don't know the answer.

    Bookmark   August 6, 2013 at 3:49PM
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Ibewye

Ronnatalie-interesting comment. You do remember asbestos and lead paint were considered safe and allowable per code? So you understand that because something is allowed per code doesn't mean that it's the best idea.
You mentioned that PVC isn't allowed in plenum spaces, why? PVC is durable enough to withstand the elements outside, it can withstand a lot of abuse and is cheaper than EMT conduit, so why isn't it more readily used in non-plenum rated spaces in schools or commercial buildings (other than those places with chemicals that would eat away other types of conduit)?
-Why have airplanes banned the use of PVC wiring in any new airplanes?
-Why have fire departments supported the reduced usage of PVC in buildings?
-It's kinda scary that PVC isn't effectively recycled because its toxicity levels can contaminate batches that are safe for the recycling process. (That little recycling triangle-if it has "3", its PVC)
-Does it matter to you that it only needs to smolder (not even ignite) to release hydrogen chloride gas (which tends to be colorless) so although an area appears to be smoke free, the unexpected inhalation of the fumes is often the cause or the death, given the low melting point it's a serious concern.
So I apologize for the audacity to think that someone might be interested any information outside of the "scope" of the NEC, or any silly health concerns that are relevant to their question. Maybe if the code mentioned that corporations such as Microsoft, Honda, Johnson and Johnson, Nike, Toyota and (the ethical juggernaut) Wal-Mart have begun efforts to reduce and phase out PVC usage in products. I guess I choose morals over code when it comes to my comments and we'll have to agree to disagree.

    Bookmark   August 6, 2013 at 11:22PM
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bus_driver

The use, or not, of PVC is not a code issue in residences and thus is simply a matter of individual choice.

    Bookmark   August 7, 2013 at 7:36AM
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Ron Natalie

Oh, so you want to cover up your misinformation by throwing personal insults at those who give the correct and safe information? Actually the NFPA, who draft the NEC, is *WAY* more safety proactive than many of the other building codes.

PVC conduit as well as just about anything else other than metal or high temperature jacketed (i.e., teflon) cables are prohibited from environmental airspaces (ducts, plenums, etc...) because these are more sensitive areas (can be directing the toxic emissions to other sections of the structure than just where the fire is).

The basic reason for avoiding it is the CODE explicitly says it is not permitted. If you want to go through the years of NFPA, UL, CPSC testing on something to prove that it is safe in light of what the industry has already determined, go to it, but most of us here ARE BOIUND by what the code says not what you feel is goo ror not.

    Bookmark   August 7, 2013 at 8:20AM
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Ibewye

Please point out my misinformation, I said I can't cite a code that says PVC isn't allowed in buildings. That's true, I cannot. I did say that generally its not used because there is health risks involved using it, therefore not making it a good choice to run in your home either. are you denying that PVC pipe poses a health risk in the event of a fire, that it has a lower melting point thus making it one of thn first materials that would be likely to release toxic fumes. Fumes thar are difficult to see because they are colorless.
I'm well aware of the reasoning for the code to restrict cabling in plenum spaces, enough so to point out that yes the toxins are reason enough but its more so to avoid the black smoke that fills a room when jacketed cable burns. Limiting visibility. Which is how plenum rated cable came to be. You still can't breathe it, but you'll be able to see.
If you believe I took a personal attack at you it's because you took it personally, after all I'm bound by the terms and conditions of this site not by what hurt your feelings. So again, a member asked if PVC is allowed in a house and yes it is, but from someone who can looks past the black and white of the code and offer insight to pros and cons of the accepted methods. It's kinda pointless to participate in a forum that basically reduces every question to "is" code or "isn't" code, what else could there be.

    Bookmark   August 7, 2013 at 12:22PM
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greg_2010

ibewye, I'm not arguing against you (because I really don't know the answer one way or the other) but where did you get your info about pvc?

I did a quick google search and came up with the linked site below (as well as a few more that I glanced at). It basically states the opposite of what you are saying. PVC has good fire retarding properties. I can't vouch for the validity of it's claim but I just found it interesting that it was the complete opposite of what you're saying.

Can you supply any sources to back up your claim?

Here is a link that might be useful: pvc fire retardant properties

This post was edited by greg_2010 on Wed, Aug 7, 13 at 14:09

    Bookmark   August 7, 2013 at 2:01PM
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petey_racer

I would hate a to be a person that is so paranoid that I worried about PVC electrical conduit inside a building because it might release toxins IN THE EVENT OF A FIRE.
Sorry, but that's one of the last things I'd worry about. There are FAR more important things that would concern me in the event of a fire.

    Bookmark   August 7, 2013 at 4:26PM
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Ron Natalie

Black Smoke is entirely besides the point. Lots of black smoke just means soot. The thing that will kill you are things like released HCN, etc... which by and large are INVISIBLE to you.

    Bookmark   August 7, 2013 at 5:33PM
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hexus

PVC inside a building is "bad"?
huh, guess I've been doing it wrong all these years.

I run quite a bit of PVC inside houses for sub panels. Ever since they took out the SER exception in the 2008 code forcing you to upsize.
I find it easier and faster to run PVC than EMT in those cases. I can pack a heat blanket easier than a bender

BTW - your user name says it all.....

This post was edited by hexus on Wed, Aug 7, 13 at 19:02

    Bookmark   August 7, 2013 at 6:54PM
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Ibewye

Absolutely, but before I do please understand I'm not any sort of advovate on for PVC awareness. I remember installing a pvc conduit in the drop ceiling of a school and thinking it was odd that it was cheaper and easier to install yet I rarely saw it used inside, the following week we were ordered to remove it, when I asked the reasoning I remember it was somehow linked to the toxicity levels.

Black smoke is not really besides the point, its part of the point. You said it yourself many materials are toxic, plenum spaces requirements come from more than the just the hopes of reducing toxins. Copper acting as a catalyst from the inside can have some nasty effects when mixed with the low melting point of plastics, one of the biggies is a bellowing black smoke that is spread rapidly through a ventilation system. Plenum rated cables are designed to reduce the levels.

Petey_Racer I agree I would hate to be someone who was paranoid about the toxin levels of PVC also. Luckily I've spent less than 30 minutes on the dangers of it and 29 of them were yesterday. I'd rather spend time browsing these boards and if I can add some insight that I think is relevant to a question then I'll choose to do so. If this forum is only to discuss what the NEC code does or does not permit and shuns the most minute mentioning of safety concerns or even worse, an opinion then it should re-titled. If not, then I guess as it stands I leave my opinion at the door- electrical PVC is permitted to be installed but you don't see it very often, as their are other options available,consider Emt or fmt as a raceway.
Here's the first link I found and a quick quote that I found on it.
http://en.m.wikipedia.org/wiki/Polyvinyl_chloride

"February 2007, the Technical and Scientific Advisory Committee of the US Green Building Council (USGBC) released its report on a PVC avoidance related materials credit for the LEED Green Building Rating system. The report concludes that "no single material shows up as the best across all the human health and environmental impact categories, nor as the worst" but that the "risk of dioxin emissions puts PVC consistently among the worst materials for human health impacts."[47]

    Bookmark   August 7, 2013 at 7:12PM
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Ibewye

I guess I'll take the time do the research and clear the air on any misinformation regarding how much "black smoke" is the point, its actually the whole point.
http://en.m.wikipedia.org/wiki/Plenum_cable
http://www.l-com.com/multimedia/datasheets/DS_CABLE_FLAMMABILITY_RATINGS.PDF
http://www.hyperline.com/info/sprav/cable01.shtml

    Bookmark   August 7, 2013 at 7:33PM
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steve_fl

How in the world did we go from the OP questions-
1. Can the THHN be run like Romex (through drilled holes between joists, stapled to wall studs)? Or must they be run in conduit?

2. If conduit is a requirement, must I use metal conduit?

3. If I can use plastic conduit, may I tie in plastic conduit to the metal junction box which holds the feed?

to all this discussion of smoke/fumes/toxicity/etc?????
Let's keep it on topic and forget the pettiness and one-up-manship, and stick to the topics at hand, answering questions of DIY'ers and giving sound electrical advice!

    Bookmark   August 7, 2013 at 9:06PM
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Ron Natalie

The question was answered in the first few posts. That is, you can not run THHN exposed. It has to be in conduit or raceway. PVC rigid conduit can be used in the places for which it is allowed and not prohibited. Exposed and concealed indoor use in residences (except in certain limited situations) is permitted. Any sort of conduit or cabling requires a listed fitting to connect it to a junction box or panel enclosure and such are readily available.

It only got weird when certain people started injecting spurious (and not supported by the code) into the situation and decided to argue like a two-year old with those who pointed out he was wrong.

    Bookmark   August 8, 2013 at 7:13AM
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elltwo

I've read and re-read this thread several times and have seen no one arguing like a two-year old and have seen no one proved wrong. I've seen a link to a site run by the pvc industry and a snide remark about a user name from hexus:

"PVC inside a building is "bad"?
huh, guess I've been doing it wrong all these years.

I run quite a bit of PVC inside houses for sub panels. Ever since they took out the SER exception in the 2008 code forcing you to upsize.
I find it easier and faster to run PVC than EMT in those cases. I can pack a heat blanket easier than a bender

BTW - your user name says it all..... "

It's nice to see comments from a common sense point of view about products of combustion and their effects on human health.

    Bookmark   August 8, 2013 at 7:50AM
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hexus

I honestly couldn't care any less if you think my comment was snide. The person was flat out wrong. I can't stand people that push their opinion as "law" when they have nothing to back it up with. The only thing proven was that the person knows how to use google.
I think that if PVC inside of a building was such a concern somewhere along the lines concrete evidence would have been presented and codes would have been changed. Instead you're going off some random guy on the internet that can use google for a few minutes.

where's your common sense now?

    Bookmark   August 8, 2013 at 9:12AM
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petey_racer

Ibewye , if your name is any indication as to your background THAT is the reason you don't see much PVC. It's simply too easy and too cheap to install. Both opposite trademarks of union work.

    Bookmark   August 8, 2013 at 7:36PM
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Ibewye

Truth be told Petey_Racer, I would hope your professional enough to know whether your in a union or not should have no effect on whether or not your gonna follow code. If I'm in a "place of assembly" and code says no pvc than so be it, on the flip side of that I've also learned the hard way that NEC code is not law. Code or not if its falling short of meeting a standard for local fire codes or any other fire rating specs, the NEC faces a tough battle.
It's been nice to see this forum come alive for a little while and truths is there's a gray area to alot of things. Just think if I had told you a few years ago that installing a good 'ol duplex receptacle in my new house would be a code violation.
Sadly, I see that you've reverted to the typical union stereotypes and rhetoric which is usually shows your out of anything worthy of discussing. I work with lots of non-union vendors in many of the plants I work in. Luckily were civil enough to look past that stuff and focus on working together.

    Bookmark   August 8, 2013 at 8:39PM
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Ibewye

Truth be told Petey_Racer, I would hope your professional enough to know whether your in a union or not should have no effect on whether or not your gonna follow code. If I'm in a "place of assembly" and code says no pvc than so be it, on the flip side of that I've also learned the hard way that NEC code is not law. Code or not if its falling short of meeting a standard for local fire codes or any other fire rating specs, the NEC faces a tough battle.
It's been nice to see this forum come alive for a little while and truths is there's a gray area to alot of things. Just think if I had told you a few years ago that installing a good 'ol duplex receptacle in my new house would be a code violation.
Sadly, I see that you've reverted to the typical union stereotypes and rhetoric which is usually shows your out of anything worthy of discussing. I work with lots of non-union vendors in many of the plants I work in. Luckily were civil enough to look past that stuff and focus on working together.

    Bookmark   August 8, 2013 at 8:40PM
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petey_racer

Well, the first part of your reply has nothing to do with the discussion. The second part is typical thin-skinned union defensiveness.

Sorry, but in my experience, the easier, cheaper or more convenient way is never the union way. If something takes more time or is more expensive that's the way they go. I have not reverted to rhetoric or stereotypes, I am speaking from experience. If in your opinion that renders me uncivil or unworthy of discussion you are more than welcome to ignore me.

    Bookmark   August 8, 2013 at 9:37PM
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bus_driver

The IBEW and other unions are represented on the panels that write and revise the NEC. The proposals from those union representatives always favor the rules that increase labor and material content in the electrical requirements. You pay more as result
Affordable housing indeed.

The makers and unions involved in steel conduit have protested regularly against the approval of use of any non-metallic conduit. I recall the protests about ENT and the severe limitations initially imposed on where and how it could be installed. For the 2011 NEC, the Code-Making Panel No.8 dealing with some of the conduit Articles included a representative of The Aluminum Association, Inc., one from American Iron And Steel Institute and one from International Brotherhood of Electrical Workers. There were two representatives of the "plastics" industry. So some balance, but tilted away from the non-metallics.

This post was edited by bus_driver on Fri, Aug 9, 13 at 9:18

    Bookmark   August 9, 2013 at 7:36AM
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