Non-Metallic box for light fixture crossbar needs grounding?

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Read my previous posts
I read what you said. You claimed that the little screw recess in the box effectively insulates the screw head. I don't see how it does anything of the sort if a wire nut comes loose. The end of the wire can go anywhere.

One of the problems I have always had with the term "likely" is that the code uses it but never defines it in some useful way.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
I read what you said. You claimed that the little screw recess in the box effectively insulates the screw head. I don't see how it does anything of the sort if a wire nut comes loose. The end of the wire can go anywhere.

One of the problems I have always had with the term "likely" is that the code uses it but never defines it in some useful way.

Of course it can but the nec appears to accept the recess as a safe bet.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
We talked about this here before. They do make a plastic fixture box with a ground screw that is part of a metallic insert that the fixture screws thread into. I think it was Code in some jurisdiction to use them for fixtures.

-Hal
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
If there are metal screws that protrude into the plastic box then that is an issue. The ones I have seen have the screws recessed as shown in the picture for the switch box... same idea but for a round box.

 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
Of course it can but the nec appears to accept the recess as a safe bet.
I don't think the NEC is worried about an internal box mounting screw becoming energized. However, it is concerned about energizing a mounting bracket that could be contacted by a person, such as a luminaire canopy.
 

eds

Senior Member
Do the 8/32's typically used to mount the fixture to the strap provide a bonding means? Why would the crossbar need a different size egc from the fixture they are part of the listed fixture.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Do the 8/32's typically used to mount the fixture to the strap provide a bonding means? Why would the crossbar need a different size egc from the fixture they are part of the listed fixture.
Consider a steel box because plastic boxes are relatively recent. The mounting bracket, hence the fixture, was always bonded to the steel box by virtue of the screws and direct contact. Now along comes non-metallic boxes. The mounting bracket still needs to be bonded so the fixture manufacturer provides a green bonding screw on the bracket with the assumption that the installer would either provide an EGC pigtail or extend the EGC from inside the box to the screw. But because that isn't always going to be followed especially by homeowners and DIYs, some jurisdictions wanted the same assurance that a steel box provides and that is what that fixture box that Dennis posted a picture of does.

-Hal
 

eds

Senior Member
If I were to use the non metallic box like Dennis posted, then I would not have to make up the fixture egc to the branch circuit egc. (for sake of discussion). I still feel that the 8/32's will provide a bonding means with the box posted or with a standard fiberglass box and metal strap.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If I were to use the non metallic box like Dennis posted, then I would not have to make up the fixture egc to the branch circuit egc. (for sake of discussion). I still feel that the 8/32's will provide a bonding means with the box posted or with a standard fiberglass box and metal strap.
If you use the box that Dennis posted the brach circuit EGC would go to the green screw and the EGC from the fixture would go to the green screw on the fixture bar. They do not need to be spliced together.
 

eds

Senior Member
I understand that concept, I guess my logic is on a standard plastic or fiberglass box with out the ground strap. The fixture strap will be bonded to the egc via the 8/32's used to attach the fixture to the strap.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I understand that concept, I guess my logic is on a standard plastic or fiberglass box with out the ground strap. The fixture strap will be bonded to the egc via the 8/32's used to attach the fixture to the strap.
So you're saying that you're relying on the fixture to bond the strap?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
That's a violation. As Dennis stated the EGC must connect to the bar.
250.148(B) Grounding Continuity. The arrangement of grounding connections shall be such that the disconnection or the
removal of a receptacle, luminaire, or other device fed from the box does not interfere with or interrupt the grounding continuity.
 
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