Wire Type

Tim Ganz · Apr 30, 2014

I ordered some MTW wire to use inside my panel and THHN for field wiring but the distributor shipped TFFN in the place of THHN.

Is TFFN a good replacement for THHN pulling through conduit? The TFFN feels more like MTW than it does THHN.

Bob Mattos · Apr 30, 2014

TFFN is generally only smaller wire (16 or 18awg) and has a lower heat resistance. It is also not good for any wet location.

Tim Ganz · Apr 30, 2014

This post shed some light on it http://forums.mikeholt.com/showthread.php?t=83841

Looks like THHN is not available below 14 AWG. But will this 16AWG TFFN be ok to pull in conduit or would it be better to send it back and get 14 AWG THHN?

Bob Mattos · Apr 30, 2014

I would say it depends on the application. I would guess that in Texas you might want the THHN

T Gibbs · Apr 30, 2014

If the conduit is in a dry location and the voltage on the wiring is 24 or something like that, I would use it. I don't use anything smaller than 14 for line (120) voltage.

OkiePC · Apr 30, 2014

My preference for 16awg control wiring is to use multi-conductor cable in the conduit between boxes, you will be surprised how small 18 to 25 conductors can be, and you can get them colored and or numbered about however you like. Lapp cable is one maker who comes to mind, and we have used Alpha brands too.

http://www.alphawire.com/en/Product...ontrol-Industrial-Cable/Communication-Control

http://www.lappusa.com/10140description.htm

James Mcquade · Apr 30, 2014

check the wire and wire spool. the wire might have a dual rating.

watch out for conduit conductor fill, wire derating and heat derating. they can haunt you sometimes.

regards,
james

jraef · Apr 30, 2014

Tim Ganz said:
I ordered some MTW wire to use inside my panel and THHN for field wiring but the distributor shipped TFFN in the place of THHN.

Is TFFN a good replacement for THHN pulling through conduit? The TFFN feels more like MTW than it does THHN.

TFFN is only available in 16ga and 18ga, so you must have tried to buy 16ga or 18ga THHN.

You cannot pull individual conductors in conduit that is under 14ga wire. Smaller wire can be used inside of things like control panels and fixtures, and it can be used in larger bundles like control cable and tray cable, but not pulled in conduit in the field as single conductors. So there is no reason for anyone to make 16 and 18ga THHN.

T Gibbs · May 1, 2014

jraef said:
TFFN is only available in 16ga and 18ga, so you must have tried to buy 16ga or 18ga THHN.

You cannot pull individual conductors in conduit that is under 14ga wire. Smaller wire can be used inside of things like control panels and fixtures, and it can be used in larger bundles like control cable and tray cable, but not pulled in conduit in the field as single conductors. So there is no reason for anyone to make 16 and 18ga THHN.

In Class 1 circuits, you can use 16 or 18 awg in conduit. Refer to NEC article 725.

Tim Ganz · May 2, 2014

So it will be ok to pull the TFFN in conduit?

T Gibbs · May 2, 2014

Yes, as long as it's not being used for general power and lighting circuits. 16 is limited to 10 amps and 18 to 7 amps.

Tark · May 2, 2014

And it isn't being installed in a Damp or Wet location. So the conduit(s) can't go underground, can't be in concrete slabs, not exposed to liquids. Obtain a copy of the NEC for more detailed information on Damp and Wet location definitions.

Tim Ganz · May 2, 2014

It will be in rigid conduit in a dry area and will only be for PLC IO and interlocking control circuits some at 24 DC and some at 120 AC.

T Gibbs · May 2, 2014

I would run them in separate conduits and use 14 for the 120vac wiring. Nec does allow it in 16, but I generally only use it for 24v.

allscott · May 2, 2014

T Gibbs said:
I would run them in separate conduits and use 14 for the 120vac wiring. Nec does allow it in 16, but I generally only use it for 24v.

Can I ask why? 16AWG is my default wire size for field I/O 24V or 120V. I just find it easier to work with.

Wire Type

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