Single Conductors

Rock86

Member
Location
new york
Let's get the critics out of the way first... I am an electrical engineer with an additional degree in electrical construction, as well as time spent in the trade. I would never design or construct an unsafe environment for anyone and the following question is to serve as an educational tool only. ;)

My boss came to me and asked a simple question which no one seems to have truly answered. Where does the code explicitly state that single conductors such as THHN, THWN, etc., must be run in conduit?

I know the first person will answer.. NEC 300.3(A) "(A) Single Conductors. Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3." And even 310 says the same thing... But as my boss and I discussed after reading through Chapter 3 carefully, what "recognized wiring method", as side from subject to physical damage, prohibits a single conductor to be run say in a wall or other open spaces freely? You can buy single conductors marked "direct burial" in which case conduit is not required... so where is the line drawn? I would like a documented code, standard, something concrete other than "because thats the way we do it" response, please... if possible.

Back story, the topic came up because we are on a job where the building was up graded and we found the service entrance cable in a crawl space under the upgrade, breaching through a layer of item-4 and then diving back down in. No sign of conduit on either end. At the meter, there was a conduit sub up.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
My boss came to me and asked a simple question which no one seems to have truly answered. Where does the code explicitly state that single conductors such as THHN, THWN, etc., must be run in conduit?

I know the first person will answer.. NEC 300.3(A) "(A) Single Conductors. Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3." And even 310 says the same thing... But as my boss and I discussed after reading through Chapter 3 carefully, what "recognized wiring method", as side from subject to physical damage, prohibits a single conductor to be run say in a wall or other open spaces freely?
Take a look at Article 394. :cool:

-Hal
 
There isn't a chapter 3 wiring method called "thhn conductors through bored holes in framing members" :happyno:

I don't think there is any reasonable argument for single conductors in walls being "directly buried" :lol:
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
electrofelon said:
There isn't a chapter 3 wiring method called "thhn conductors through bored holes in framing members"
Art 394 but I'm not trying to agree with these guys.

Rock86 said:
But as my boss and I discussed after reading through Chapter 3 carefully, what "recognized wiring method"...prohibits a single conductor to be run say in a wall or other open spaces freely?
Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3.

It's not like this is a bad translation from Chinese. "Recognized wiring method" doesn't prohibit anything. "Shall only be installed" is what does.

Plain English to me. Both of you need to read it again. :happyyes:

-Hal
 

Rock86

Member
Location
new york
Thanks guys! (Ladies, gentlemen, others... whatever you choose just using guys as a general term so don't shoot me),

394 was our only go to as well, but if you use the phrase "Knob and Tube" you're bill automatically becomes the cost of a new house hahaha.

I guess I was hoping for something a little more solid. And yes "shall only be installed" is plain English, but the interpretation what wiring method it shall be installed by seems to be our thought. I'm not saying loosey goosey is a recognized wiring method.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
I think the key phrase here is, "wiring method." What does that mean? For example, if I take a #12 THHN, attach a lug to one end, and screw it onto a terminal block, is that a "wiring method"? If I take the same wire, this time without a lug, and wrap the end around the terminal of a switch and then tighten the screw, is that a different "wiring method"? Or does that phrase refer to how wires are routed from one place to another? For example, are running one set of conductors in EMT and another set of conductors in PVC different "wiring methods"?
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
394 was our only go to as well, but if you use the phrase "Knob and Tube" you're bill automatically becomes the cost of a new house hahaha.
Knob & Tube can't be used in new construction.

I guess I was hoping for something a little more solid. And yes "shall only be installed" is plain English, but the interpretation what wiring method it shall be installed by seems to be our thought.
Any of the wiring methods in Chapter 3 of your choosing that you would run individual conductors with. Tubing and all the various types of conduit are available, for example. Obviously the cables already have the conductors within them.

-Hal
 

romex jockey

Senior Member
Location
Vermont
Perhaps>>>

Chapter 9 Tables

(9) A multiconductor cable, optical fiber cable, or flexible
cord of two or more conductors shall be treated as a
single conductor for calculating percentage conduit or
tubing 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.
~RJ~
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Perhaps>>>

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.

~RJ~
Which makes 3-cond UF in conduit a particularly crappy combination.
 

tortuga

Senior Member
Location
(44.057116, -123.103394)
Occupation
field supervisor
we found the service entrance cable in a crawl space under the upgrade, breaching through a layer of item-4 and then diving back down in. No sign of conduit on either end.
The above installation is in violation of 2017 NEC 300.5(C) and 300.5(D)
one could reach for 110.3(B) 'service entrance cable' is listed in the UL white book:
SERVICE-ENTRANCE CABLE (TYLZ)
GENERAL
Types USE and USE-2 — Indicates cable for underground installation
including direct burial in the earth. Maximum size is 2000 kcmil. Cable in
sizes 4/0 AWG copper, aluminum or copper-clad aluminum and smaller
and having all conductors insulated is suitable for all of the underground
uses for which Type UF cable is permitted by the NEC. Multiconductor
Type USE cable contains conductors with insulation equivalent to RHW or
XHHW. Multiconductor Type USE-2 contains insulation equivalent to
RHW-2 or XHHW-2 and is rated 90°C wet or dry. Single- and multicon-
ductor Types USE and USE-2 are not suitable for use in premises. Single-
and multiconductor Types USE and USE-2 are not suitable aboveground
except to terminate at the service equipment or metering equipment.
Both
the insulation and the outer covering, when used, on single- and multi-
conductor Types USE and USE-2, are suitable for use where exposed to
sun.


I think the key phrase here is, "wiring method." .../snip/...are running one set of conductors in EMT and another set of conductors in PVC different "wiring methods"?
Yes I think so.

To completely answer the question though, you could go to probably the first wiring 'method' in the code 'open wiring on insulators' ART 398, now only allowed for industrial or agricultural establishments.
 

Rock86

Member
Location
new york
I think the key phrase here is, "wiring method." What does that mean? For example, if I take a #12 THHN, attach a lug to one end, and screw it onto a terminal block, is that a "wiring method"? If I take the same wire, this time without a lug, and wrap the end around the terminal of a switch and then tighten the screw, is that a different "wiring method"? Or does that phrase refer to how wires are routed from one place to another? For example, are running one set of conductors in EMT and another set of conductors in PVC different "wiring methods"?
This is what I am trying to find out.
 
Interesting results when you Google 'wiring methods'

Basic Wiring Methods Cleat Wiring. Here, PVC insulated cables are used. ...
Casing and Capping Wiring. The cable runs through a wood casing that has parallel grooves that appear at regular intervals along it. ...
Batten Wiring. Batten wiring is one of the basic wiring methods that is used today. ...
Conduit Wiring.
 

tortuga

Senior Member
Location
(44.057116, -123.103394)
Occupation
field supervisor
My boss came to me and asked a simple question which no one seems to have truly answered. Where does the code explicitly state that single conductors such as THHN, THWN, etc., must be run in conduit?
It doesn't

I know the first person will answer.. NEC 300.3(A) "(A) Single Conductors. Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method .
NEC 300.3(A) is basically saying all wiring methods are prohibited unless they are described in a chapter 3 article, so for example wiring with flexible cord is not an approved 'wiring method'.
So permissible wiring methods are in articles 300 - 399.


... as my boss and I discussed after reading through Chapter 3 carefully, what "recognized wiring method", as side from subject to physical damage, prohibits a single conductor to be run say in a wall or other open spaces freely?
All chapter 3 wiring methods except Article 394 and 398 prohibit a single conductor to be run in a wall.


...
You can buy single conductors marked "direct burial" in which case conduit is not required... so where is the line drawn? I would like a documented code, standard, something concrete other than "because thats the way we do it" response, please... if possible.
110.3(B)
Do you have a copy of the UL white book?
Its a free download.
 

kwired

Electron manager
Location
NE Nebraska
Take a look at Article 394. :cool:

-Hal
as well as 396 and 398. All have limitations but are a chapter 3 wiring method.

You can buy single conductors marked "direct burial" in which case conduit is not required... so where is the line drawn?
Conduit is not required where it is directly buried and under the required cover in 300.5 Where it is not directly buried it still must be within a chapter 3 method.
 
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