ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Single phase and what you call it.
by dsk. 11/12/18 11:10 AM
220/230/240V 60Hz Systems
by Albert. 11/07/18 12:48 AM
Black & Decker Recalls Hammer Drills
by Admin. 11/01/18 07:22 PM
Having around 30 projectors to dump
by gfretwell. 10/31/18 10:54 PM
Installing a small swimming pool
by TimothyHallam. 10/30/18 10:42 PM
New in the Gallery:
What is this for?
Plug terminals
Who's Online Now
0 registered members (), 4 guests, and 27 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
404.8(B) revision - voltage between switches #79552
01/03/02 08:50 AM
01/03/02 08:50 AM
M
mlundy  Offline OP
Junior Member
Joined: Jan 2002
Posts: 2
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.

2017 / 2014 NEC & Related Books and Study Guides
Re: 404.8(B) revision - voltage between switches #79553
01/03/02 11:15 AM
01/03/02 11:15 AM
R
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
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)
Re: 404.8(B) revision - voltage between switches #79554
01/03/02 01:53 PM
01/03/02 01:53 PM
P
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
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.


Featured:

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

 

Member Spotlight
richard
richard
L.I. New York
Posts: 98
Joined: August 2003
Show All Member Profiles 
Top Posters(30 Days)
Admin 8
Popular Topics(Views)
251,429 Are you busy
188,645 Re: Forum
178,344 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.025s Queries: 14 (0.004s) Memory: 0.9523 MB (Peak: 1.0760 MB) Zlib enabled. Server Time: 2018-11-14 09:36:22 UTC