Does THHN/ Single Conductors have to be in conduit?

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Uhtredwicked

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Asheville, NC
I have always been led to believe that single strand wire needs to be run in conduit and may not be run inside the walls of a home or building. Such as THHN feeder wires for a sub-panel or some such. However, after looking in the code book, article 300.3(A), states: single conductors specified in table 310.104(A) shall only be installed where part of a recognized wiring method of chapter 3.
Chapter 3 certainly doesn't state that I may run single wire in the wall but it doesn't exactly forbid it either. Can someone help me shed some light please thank you.
I have only found a couple of similar threads on this subject and nobody seems to know a definitive answer.
 
No, you cannot run THHN inside walls "free air". You quoted the exact requirement where it says

"shall only be installed where part of a recognized wiring method of chapter 3. "

Chapter 3 wiring methods include conduit, wireways, ac and mc cable, NM cable, and so forth. So single conductors must be installed in one of these methods.

Since you are using THHN, I assume this is for 120V or 240V circuits. The reason I mention this, is that it might be possible to use THHN without a Chapter 3 method for some low voltage applications, or some other Article 700 or 800 application. But I'm not really sure about that either.




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steve66 said:
No, you cannot run THHN inside walls "free air". You quoted the exact requirement where it says

"shall only be installed where part of a recognized wiring method of chapter 3. "

Chapter 3 wiring methods include conduit, wireways, ac and mc cable, NM cable, and so forth. So single conductors must be installed in one of these methods.

Since you are using THHN, I assume this is for 120V or 240V circuits. The reason I mention this, is that it might be possible to use THHN without a Chapter 3 method for some low voltage applications, or some other Article 700 or 800 application. But I'm not really sure about that either.




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You may get away with it but generally you still are supposed to use a method identified as CL2 or other purpose that applies.

Some other instances where it doesn't necessarily need to be in a Ch 3 wiring method is bonding/grounding conductors, places where open conductors in free air are allowed and direct burial rated conductors, though DB typically needs to be in a wiring method where it emerges from grade.
 
Welcome to the Forum !

Uhtredwicked said:
I have always been led to believe that single strand wire needs to be run in conduit and may not be run inside the walls of a home or building. . .

However, after looking in the code book, article 300.3(A), states: single conductors specified in table 310.104(A) shall only be installed where part of a recognized wiring method of chapter 3.
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OK. I can't resist this one. Only part of the wiring methods in Chapter 3 are "raceway" ("conduit") methods.

Consider the conductors allowed in Articles 394, 396 & 398. When I read your post, I immediately thought about concealed Knob & Tube. I work in an area that has installed concealed Knob & Tube, as put into buildings during the first half of the Twentieth Century, that is still in service and will likely be in service for many years to come. Occasionally I find myself involved with maintaining an existing installation that needs maintenance or repair, and I am instructed by Rule 394.104 that I may use "single strand wire". Arguably a THHN conductor used in concealed K & T has long portions of which would be considered in "free air" between knobs.
 
hbiss said:
I'm assuming that because I don't think he isn't asking about K&T.
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Your double negative is confusing. All I am doing is speaking to the OP's words:

Uhtredwicked said:
I have always been led to believe that single strand wire needs to be run in conduit and may not be run inside the walls of a home or building. Such as THHN. . .
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hbiss said:
Ok, how is this:

That is correct with the exception of K&T wiring within the confines of Art. 394. :)

-Hal
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394 is for concealed Knob and tube wiring, and 394.10 allows it only for extensions of existing systems. 398 is the article your thinking of 'open wiring on insulators', its still allowed where exposed like in an attic or 7' above floors. There is a coffee shop around here that has all exposed 'open wiring on insulators' on its ceilings done really well. Its in a newer commercial building so someone got it inspected.
The knobs and tubs are pretty easy to find on resi remodel type jobs, but the porcelain box connectors are more rare.
 
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