Hello,

Another stumper of a question for me I could use some help with, even when I have the answer.

Here's the question:
"A "tap"transformer supply can use NM cable on the secondary side."
True or False

And the given answer:
"No 240.21(B)(3)(4)"

I just don't get this question at all.

Here's the code text from 240.21(B)(3)(4):
(4) The primary and secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

This would lead one to look at Article 334, NM cables, Yes?
Well, I have and don't see any relation to the question. 334.15(B) talks about Physical Damage Protection.

Before I even had the answer to this question I was stumped. I researched the following code threads without luck:
-Feeder Taps
-Transformers - in Article 250
-NM Cable, Art.334
-Separately Derived Systems
- Index lookup - Transformer ->Tap (nope) & Secondary Ties (no info), Taps -> Separately Derived Systems (No luck) & 250.30(A)(6)
-Internet searching -> no leads!!

What am I missing or is this question flawed?

Thanks,
Phil

It is not normal practice to put cables in pipe. I assume that is were they are going. "NM" implies simply using a cable and no raceway.
If perchance someone did stuff some NM in an EMT system I suppose it would be hard to fail but I would expect some funny looks.

Wow, that seems like a very oddball question.
Thanks for the explanation <:
Phil

Was this an isolated question or was it associated with a specific configuration and transformer tap conductor length? In particular, 240.21(B)(3) addresses taps supplying a transformer where the primary plus secondary length is not over 25 feet and clause (4) requires a raceway or other approved means. That's why NM cannot be used in that situation (unless in a raceway).

In fact, if you look at 240.21(B)(2 thru 4) each of the situations described has a clause requiring tap conductors to be in a raceway or other approved means. 240.21(B)(1) is slightly different, but still has a raceway requirement.

A suggestion - if you're only using the NEC manual for your studies, try to obtain a copy of the NEC Handbook. It contains the NEC manual and its purpose is to illustrate and help clarify NEC "gobbledygook" (at which it's only partially successful - you'll still have bald patches from scratching your head over NEC meanings.)

As said above, a current Handbook is worth it's weight in gold for sure!

Using the quoted code "And the given answer:"No 240.21(B)(3)(4)"

I guess the quoted Article (in a stretch) could be cited as there is no AWG for the NM given. The stretch is compliance with "ALL" ((1) thru (5) and (1) thru (9) line items within 240.21 (B) (3) and (4)

18 yrs of being an inspector, and 50 years in the trade, I have never come upon NM for a transformer secondary.

I'm thinking that maybe the purpose of the question was really about tapped conductors requiring raceway for this case (transformer) and NM was simply the cable used to make the point.

I never saw NM in any commercial installation. It was always EMT and maybe some FMC or MC cable for whips.

Thanks All <:

Good News!!

I passed!!

Whew, tough test!

Thanks for all the support.
This forum helped alot <:
Phil

Congrats!!!

Don't be a stranger here at ECN....

Ditto!!