Section 250.21(D) in NEC circa 1990

[Ground Loop Guru]

I lecture and write about ground loops in AV systems of all kinds. I have an old note in my files about this section of NEC that specifically prohibits the interruption of the equipment ground connection for plug-and-cord connected equipment (the use of 3-to-2 prong adapters to solve hum and buzz problems in AV systems is on the rise and some new products like "Hum-X" are highly suspect of being totally inadequate to carry actual fault currents (which can range from 100 A to 1,000 A in typical residences, according to a UL study). Was the prohibition in the old (1990)NEC? Do I have the section number wrong? Is the prohibition in the new edition of NEC? Perhaps someone out there has a copy of the old NEC that was in effect back then. Or perhaps I'm just going crazy! ... I have only a 2005 copy of NEC on my bookshelf

 

[ActionDave]

This is the first thing that comes to my mind. It is from the 2011 NEC

406.4 General Installation Requirements......

(B) To Be Grounded. Receptacles and cord connectors
that have equipment grounding conductor contacts shall
have those contacts connected to an equipment grounding
conductor.

 

[tom baker]

I remember that rule. I used to see portable pumps with a ground pin that was hinged. Fire guys had them.

 

[Ground Loop Guru]

What I remember is specific language, using the word "interrupt" if I recall correctly, about the EGC on cord-and-plug connected equipment. I'm trying to find exactly where, and in what year (1990 according to my cryptic note), it appeared in NEC. If it existed at all, perhaps it was deleted from current NEC. Anyone know where I could browse NEC 1990 on-line?

 

[RB1]

The relevant section of the 2008 Code is 250.6(D). This section was 250.21(D) in the 1990 Code.

 

[RB1]

See 250.6(D) of the 2008 NEC

 

[Ground Loop Guru]

Section 250.21(D) in NEC circa 1990

My thanks to all who replied ...

Bill Whitlock, president & chief engineer, Jensen Transformers, Inc.
www.jensen-transformers.com