THHN wiring - Electrician Talk - Professional Electrical Contractors Forum

heel600 · 10-31-2009, 12:17 AM

What code prohibits THHN from being used when NOT in a conduit (or tubing)?

Could I use it for class 2 wiring w/o being in pipe?

480sparky · 10-31-2009, 01:04 AM

300.3(a).

hbiss · 10-31-2009, 01:07 AM

No. THHN by itself is not listed as CL2. See the table in 725.

-hal

heel600 · 10-31-2009, 05:48 PM

Quote:

Originally Posted by 480sparky

300.3(a).

I do all my septics with 14 ga THHN for the alarm.

I run the alarm wires with the power wires. In the house, I bring the conduit in to the house, and run the conduit into a 4s box, which is fed with NM, and bring the alarm wires out through a KO and into the alarm unit.

So I take it a need to spice to NM or SJ before exiting the 4s box.

I used to use 18-2 thermostat wire, but stopped because it was not 600v rated (and I can't find it either)

Any other ideas?

jrannis · 10-31-2009, 08:20 PM

Dont bite your finger nails

jrannis · 10-31-2009, 08:23 PM

Quote:

Originally Posted by heel600

What code prohibits THHN from being used when NOT in a conduit (or tubing)?

Could I use it for class 2 wiring w/o being in pipe?

Its good for CT (cable tray) use

mattsilkwood · 10-31-2009, 09:25 PM

Quote:

Originally Posted by jrannis

Its good for CT (cable tray) use

Only if its 1/0 or larger and labeled for CT use. Article 392.
Don't ask me how I know.

hbiss · 10-31-2009, 10:13 PM

I do all my septics with 14 ga THHN for the alarm... I run the alarm wires with the power wires.

You need to become familiar with Art. 725.

By using THHN for the alarm which is probably a CL2 circuit, you are reclassifying the CL2 circuit to Class 1 by using a Class 1 wiring method. (725.52(A) exception #2) This will allow you to run those conductors with the power conductors EXCEPT for 725.26(B)(1) which states that Class 1 circuits shall be permitted to occupy the same cable, enclosure, or raceway only where the equipment powered is functionally associated.

So the question is- is it necessary for the sewage pump to have the alarm in order to operate? The answer is no, just as it has been ruled in the case of running the control wiring together with the power for rooftop AC units or even running the wiring for security cameras within outdoor light poles to which the camera is attached.

What you can do in your case to do this legally is to install a large enough conduit and pull UF through it for power. Then you are free to pull with it whatever you want for the LV alarm, even thermostat wire. The reasoning is that the UF is a listed cable assembly and the conduit then becomes a chase, much like running NM and thermostat wire in the same bay in a wall.

-Hal

jrannis · 11-01-2009, 06:16 AM

Quote:

Originally Posted by hbiss

I do all my septics with 14 ga THHN for the alarm... I run the alarm wires with the power wires.

You need to become familiar with Art. 725.

By using THHN for the alarm which is probably a CL2 circuit, you are reclassifying the CL2 circuit to Class 1 by using a Class 1 wiring method. (725.52(A) exception #2) This will allow you to run those conductors with the power conductors EXCEPT for 725.26(B)(1) which states that Class 1 circuits shall be permitted to occupy the same cable, enclosure, or raceway only where the equipment powered is functionally associated.

So the question is- is it necessary for the sewage pump to have the alarm in order to operate? The answer is no, just as it has been ruled in the case of running the control wiring together with the power for rooftop AC units or even running the wiring for security cameras within outdoor light poles to which the camera is attached.

What you can do in your case to do this legally is to install a large enough conduit and pull UF through it for power. Then you are free to pull with it whatever you want for the LV alarm, even thermostat wire. The reasoning is that the UF is a listed cable assembly and the conduit then becomes a chase, much like running NM and thermostat wire in the same bay in a wall.

-Hal

They now make a hybrid cable that contains both power and control for AC units. Ill have to dig up a link............

480sparky · 11-01-2009, 09:41 AM

Quote:

Originally Posted by heel600

i do all my septics with 14 ga thhn for the alarm.
...............
Any other ideas?

14/2nm?

mcclary's electrical · 11-01-2009, 09:49 AM

Quote:

Originally Posted by 480sparky

14/2nm?

I think he means the wires that are outside, going to the tank floats.

hbiss · 11-01-2009, 05:53 PM

Well, lets say that he did mean NM in the conduit with the THHN. First I'm going to assume that the conduit is buried so that creates a wet location. You don't want to use NM in a damp or wet location, so you are back to UF. But that creates the problem of requiring partitions in the boxes at each end to separate the THHN from the LV because 725.26(B)(1) still applies to the wiring in the boxes. I also think you would have a problem with there not being proper connectors for the UF at each end because it just exits the conduit into the boxes with the THHN conductors.

-Hal

River Boy · 11-15-2009, 08:49 PM

Quote:

Originally Posted by heel600

What code prohibits THHN from being used when NOT in a conduit (or tubing)?

Could I use it for class 2 wiring w/o being in pipe?

Most THHN is also double rated as THWN. You free air it out of weather heads all the time.

Kevin J · 11-15-2009, 11:35 PM

Quote:

Originally Posted by hbiss

Well, lets say that he did mean NM in the conduit with the THHN. First I'm going to assume that the conduit is buried so that creates a wet location. You don't want to use NM in a damp or wet location, so you are back to UF. But that creates the problem of requiring partitions in the boxes at each end to separate the THHN from the LV because 725.26(B)(1) still applies to the wiring in the boxes. I also think you would have a problem with there not being proper connectors for the UF at each end because it just exits the conduit into the boxes with the THHN conductors.

-Hal

Septic pumpback alarm and float switches are line voltage, not low voltage.

hbiss · 11-15-2009, 11:45 PM

I used to use 18/2 thermostat wire...

The OP indicated that his was LV.

-Hal

mikeg_05 · 11-16-2009, 12:02 AM

Quote:

Originally Posted by Kevin J

Septic pumpback alarm and float switches are line voltage, not low voltage.

Bingo.

Except for systems like an Aquaworks.

heel600 · 11-16-2009, 09:58 PM

yes, the alarm is LV.

I need to look up the 725 table/codes.

Thanks for everyone's help.

Never failed for the way I do it with THHN. Until I figure out a better way, I'll keep doing it this way.