ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
UL 508A SPACING
by ale348 - 03/29/24 01:09 AM
Increasing demand factors in residential
by tortuga - 03/28/24 05:57 PM
Portable generator question
by Steve Miller - 03/19/24 08:50 PM
Do we need grounding?
by NORCAL - 03/19/24 05:11 PM
240V only in a home and NEC?
by dsk - 03/19/24 06:33 AM
New in the Gallery:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
1 members (Scott35), 382 guests, and 12 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Jan 2002
Posts: 2
M
mlundy Offline OP
Junior Member
I have been reviewing changes in the 2002 NEC and had a question that I would like to get the Board's input on. Section 404.8(B) notes that if two devices (a snap switch and another device such as a switch or receptacle) are installed in an enclosure and there is greater than 300V potential difference between the adjacent devices, a barrier between the two devices must be installed.

A Code Change book that I was reading then gave an example of a switch (use to switch a 277V lighting circuit) installed next to a 120V receptacle. It indicated that the voltage between the two devices would be greater than 300V (277V + 120V). However if you were to put a voltmeter probe on one of the conductors of the 277V circuit and the other voltmeter lead on a wire from the 120V circuit, the voltmeter would read 0V because the two supplies are isolated from one another. I have read two different "2002 NEC Change" books and they both provide a similar example. What is your take on this?

I could understand that if two, 277V circuits were switched from two switches in one enclosure there would be a potential difference of 480V between the switches assuming that two different phases were used. However I don't interpret 404.8(B) the way that these two Code Change books have.

Stay up to Code with the Latest NEC:


>> 2023 NEC & Related Reference & Exam Prep
2023 NEC & Related Reference & Study Guides

Pass Your Exam the FIRST TIME with the Latest NEC & Exam Prep

>> 2020 NEC & Related Reference & Study Guides
 

Joined: Nov 2000
Posts: 2,148
R
Member
You will read voltage becuse the systems are not really isolated. They grounded conductors of both systems will be tied together by the grounding system.
Don(resqcapt19)


Don(resqcapt19)
Joined: Aug 2001
Posts: 7,520
P
Member
With a common neutral/ground the voltage you get between a 277V hot and a 120V hot will depend upon which phase of each system is present. It will certainly exceed 300V in some combinations.


Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5