National Electrical Installation Standards

Standards as High as Your Own

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Monday, June 29, 2020

Question:

Re: Code Question of the Day for May 14 Greetings Code Friends,                                                               

Question:

My question is if I have a metal outlet box and equipment grounding conductors in the box, do I have to connect the EGC to the box using a listed green grounding screw?   

Answer:

Hi Mel,

Thanks for participating. No, the connection to the metal box should be made using one of the methods provided in 250.8. If a screw is used to accomplish this connection, it should be in accordance with 250.8(5) and be a machine screw that engages not less than two threads or is secured by a nut. No requirements for such screws to be green or listed. If the connection is made with a grounding clip (pressure connector), the clip would have to be listed.                                         

Comment:

I think I know why some think that an Equipment Grounding Conductor screw must be required to be listed. I taught electrical wiring in a Vo-Tech High School for 28 years. About 15 years ago there was a textbook that stated the EGC had to be connected to metal boxes with a green listed grounding device or screw. That made it seem that the screw had to be listed and green. The actual wording in the 2002 NEC that the text book was based on said “by means of a grounding screw that shall be used for no other purpose or a listed grounding device.” (250.148(B)). It said nothing about the screw having to be listed or green. The list of permitted methods in today’s 250.8(A) did not appear until 2008. I am sure many of today’s electricians probably were exposed to that book. Before a lot of people write in saying that the screw must engage at least two threads, all 10-32 screws have 32 threads per inch, no matter what color they are or who made them.

Bob Morin

A

Answer:

Hi Bob,

Thanks for the comment and additional information. It is a good observation about the language used in the 2002 NEC in Section 250.148(B) that may very well have contributed to the gray area here. The subsequent incorporation of 250.8 has provided the needed clarity. 

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