[Elecraft] Grounding

[Jim Brown]

On Mon,9/28/2015 11:26 AM, Kenneth Talbott wrote:
> Several years ago the NEC relaxed the requirement that safety ground and
> neutral be connected at only one place.  Now you may leave the bonding screw
> in place in remote panels.

http://ecmweb.com/code-basics/grounding-and-bonding-part-2-3

The link above is from Mike Holt, widely considered an authority on 
electrical codes. He makes his living teaching and writing about the 
topic. This is part of his review of revisions to Article 250, Grounding 
and Bonding, that appeared in the 2011 code. In the very last paragraph, 
are these words:

"As a rule, the neutral should never be connected to the enclosure or 
equipment grounding conductor anywhere except in the service disconnects 
and the secondary side of separately derived systems. Objectionable 
neutral current presents a real danger and can damage equipment as well 
as cause fires and electric shock or electrocution."

For all practical purposes, the 2011 code is the most recent, because it 
usually takes 5-6 years for local authorities to adopt a revision.  Upon 
reading your email, I reviewed a draft of the 2014 code, and the 
requirement for one, and only one, neutral to ground bond is still part 
of it.

The only "remote panel" in which a bond would be permitted between 
neutral and ground is one in a second building where ground is not 
carried between buildings, or when the remote panel is for a "separately 
derived system." A system is separately derived when fed by a 
transformer. The practice of not carrying ground between buildings no 
longer permitted, but is grandfathered in existing installations from 
earlier versions of NEC.

73, Jim K9YC