ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
NEC 2017_392.22(B)(1)(b)
_What's the smallest width

by HotLine1 - 09/19/19 01:34 PM
Kichler Lighting Recalls Pendant Lights
by Admin - 09/18/19 08:47 PM
Does a 'normal 3ph-AC motor' include capacitors?
by gfretwell - 09/18/19 01:20 AM
Another weird NEC code question on Feeder Taps
by gfretwell - 09/18/19 01:14 AM
NEC Question_Cord-&-Plug EGC shorter then Neutral
by pcsailor - 09/16/19 05:26 AM
New in the Gallery:
What is this for?
Plug terminals
Who's Online Now
0 registered members (), 10 guests, and 10 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 2 1 2
Another NEC 2017 Question_240/24VAC Txfr-Neutral R #220243 09/04/19 03:06 PM
Joined: Sep 2019
Posts: 13
pcsailor Offline OP
Member
Hi,

Am I thinking correctly on this NEC2017 question?

"A 24 volt AC system fed thru a 240 volt transformer does not need to use "White" as a neutral (grounded)"
True or False

I'm thinking True based on 250.20 (p106).
But that code section doesn't exactly hit the mark. I've looked all through Article 450 and other sections but I haven't spoted this exact question terminology.

Any clues?
Thanks,
Phil


Where ever you go, there you are.
2017 / 2014 NEC & Related Books and Study Guides
Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: pcsailor] #220244 09/04/19 05:46 PM
Joined: Oct 2000
Posts: 3,923
Bill Addiss Offline
Member
I'm not sure what kind of answer they're looking for, but I would argue true based on 200.6


Bill
Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: pcsailor] #220245 09/05/19 12:26 AM
Joined: Jul 2004
Posts: 9,392
G
gfretwell Offline
Member
The only way it CAN be white is if it is a grounded conductor. If you ground one side of the secondary that conductor needs to be white or gray. Otherwise it can't be (legally) although there is plenty of red/white doorbell and thermostat wire out there. I understand we assume the rules don't really apply to low voltage systems but Article 200 doesn't say that wink


Greg Fretwell
Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: gfretwell] #220246 09/05/19 02:09 AM
Joined: Oct 2000
Posts: 3,923
Bill Addiss Offline
Member
Originally Posted by gfretwell
The only way it CAN be white is if it is a grounded conductor. If you ground one side of the secondary that conductor needs to be white or gray. Otherwise it can't be (legally) although there is plenty of red/white doorbell and thermostat wire out there. I understand we assume the rules don't really apply to low voltage systems but Article 200 doesn't say that wink

I can’t tell if you’re agreeing with me or not smile

My reading of the question is whether the grounded wire in this situation has to be white and 200.6 says it could be gray.


Bill
Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: pcsailor] #220247 09/05/19 03:50 PM
Joined: Jul 2004
Posts: 9,392
G
gfretwell Offline
Member
True. They removed "natural" (gray) a few cycles ago. That referred to the natural rubber color of the wire we now call white. Gray PVC insulated wire has been the convention for neutral in 277 (wye) for years before the change and they finally recognized it.

The open question is whether 200.6 applies to low voltage cables. If so the white wire would have to be grounded and we know it usually isn't. In fact the green wire in thermostat cable is also non compliant. I have looked but I haven't found that exception. It may be hidden somewhere tho.


Greg Fretwell
Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: pcsailor] #220249 09/06/19 09:32 AM
Joined: Jan 2018
Posts: 5
L
libellis Offline
New Member
Maybe 200.7(B)

Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: pcsailor] #220250 09/06/19 01:32 PM
Joined: Apr 2002
Posts: 7,112
HotLine1 Online Content
Member
Just IMHO, as the question specifically states the word "grounded", I would say ...TRUE.

I have not heard of any inspectors that would have any types of issue with a 'white' conductor on the secondary side of a XFR.
.


John
Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: pcsailor] #220253 09/06/19 08:48 PM
Joined: Jul 2004
Posts: 9,392
G
gfretwell Offline
Member
Yup 200.7(B) I guess I didn't look hard enough wink


Greg Fretwell
Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: pcsailor] #220267 09/15/19 12:14 AM
Joined: Sep 2019
Posts: 13
pcsailor Offline OP
Member
Here is the given answer:
"Nope  it does  250.70.A   200.7.B"

I got that wrong too. I said True based on 250.20.

So much to learn, and when I die, it's all gone <:

Thanks,
Phil


Where ever you go, there you are.
Re: Another NEC 2017 Question_240/24VAC Txfr-Neutral R [Re: pcsailor] #220269 09/15/19 04:56 AM
Joined: Sep 2019
Posts: 13
pcsailor Offline OP
Member
Some follow up notes as I dive deeper into this question and answer.

250.70(A) doesn't exist in NEC2017. Does it exist in 2014? (I don't have that codebook).
250.70(1) through (4) do exist but it has to do with grounding/bonding connections to electrodes.
I don't see any relation to this question.

200.7(B) relates to this question and points to 250.20(A).

250.20(A) is AC systems to be grounded with (A) being less than 50V.
If this transformer is fed from one 240V leg, wouldn't 250.20(A)(1) & (2) be True and therefore a Neutral required?
Which would make the question False, as is the answer given, "Nope it does 250.70.A 200.7.B"

What if the transformer is fed from two 120V ungrounded with an existing Neutral? Answer is still False.

Kind of a weird question,...and answer.
What do you think?
Am I over-thinking this one? I've been know to do that <;

Cheers,
Phil


Where ever you go, there you are.
Page 1 of 2 1 2

Featured:

2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
BEAMEUP
BEAMEUP
WA
Posts: 27
Joined: December 2004
Show All Member Profiles 
Top Posters(30 Days)
Admin 7
Popular Topics(Views)
258,695 Are you busy
194,264 Re: Forum
183,725 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3