mounting bracket that has a ground screw

[xara]

• when I install a light in a metal box : do I need to attach the grounds to an additional ground screw in the box, or is it ok to just ground the box through the mounting bracket ground screw that comes with the light?

 

[jumper]

Boxes must always be directly bonded to the EGC from the panel if the EGC is a wire type.

 

[xara]

ground screws

ground screws

why do they put a ground screw on the light mounting bracket, if there is a ground screw inside the box?

 

[jumper]

why do they put a ground screw on the light mounting bracket, if there is a ground screw inside the box?

What if it was a plastic box?

 

[mgookin]

When we get things listed, the rules are, if there's anything conductive where a human can touch it, it gets bonded.
I imagine your box manufacturer and light manufacturer go through the same rules.
If it's metal, bond it.

 

[xara]

so if it is a metal box can you use either screw or must you attach to both?

 

[jumper]

so if it is a metal box can you use either screw or must you attach to both?

Both have to be bonded. Boxes are always attached to wire EGCs. 110.3(B) and the instructions probably require that the bracket ground screw have a wire type EGC or bonding jumper also.

The bracket can not be used to bond the box.

 

[al hildenbrand]

so if it is a metal box can you use either screw or must you attach to both?

As a rule both, and sometimes in THREE places.

Think about the reliability of the electrical connection created by the luminaire mounting bracket screws. In flush installations, the bracket is against the building surface, not bolted tight to the box mounting screw ears. The installer snugs the mounting bracket against the building surface (drywall, a lot of the time). This tightening is not "bolt tight", and can work loose over time.

The metal box, if not bonded first to the branch circuit EGC, will become unbounded if the light fixture is removed.

Lastly, the luminaire may have its own EGC that must be connected to the branch circuit EGC, as well. That's the third bond.

 

[iwire]

I agree whole heartadly with Al.

 

[infinity]

As a rule both, and sometimes in THREE places.

Think about the reliability of the electrical connection created by the luminaire mounting bracket screws. In flush installations, the bracket is against the building surface, not bolted tight to the box mounting screw ears. The installer snugs the mounting bracket against the building surface (drywall, a lot of the time). This tightening is not "bolt tight", and can work loose over time.

Where is this in the NEC? Toggle switches can be grounded to the metal box by nothing more than 2-6/32 screws and they're mounted to the drywall too. If anything could "work loose over time" it would be a switch that can used many times a day.

 

[JFletcher]

I asked virtually the same question 7 months ago:

http://forums.mikeholt.com/showthread.php?t=172207&highlight=

 

[ActionDave]

When it is a metal box I don't use the green screw on the mounting bracket for anything. I do connect the light fixture to the egc.

 

[ceknight]

why do they put a ground screw on the light mounting bracket, if there is a ground screw inside the box?

Strain relief. You bond the fixture first, then land the fixture ground wire under the bracket screw also so you can let the fixture dangle while you splice everything else.

 

[luckylerado]

Strain relief. You bond the fixture first, then land the fixture ground wire under the bracket screw also so you can let the fixture dangle while you splice everything else.

:thumbsup: Exactly what I usually do.

 

[infinity]

Strain relief. You bond the fixture first, then land the fixture ground wire under the bracket screw also so you can let the fixture dangle while you splice everything else.

Yup I would do the same thing. The metallic box is grounded, the bracket is screwed to the metallic box and the fixture EGC gets terminated on the green screw on the bracket.

 

[kwired]

When it is a metal box I don't use the green screw on the mounting bracket for anything. I do connect the light fixture to the egc.

same here.

Strain relief. You bond the fixture first, then land the fixture ground wire under the bracket screw also so you can let the fixture dangle while you splice everything else.

done that also. If you hook up a different conductor first it just becomes the one that it hangs from while making up the others.

Mounting bracket is usually not any wider then the box and is usually tight to the box - unless it is a 3-1/2 inch box.

 

[al hildenbrand]

Where is this in the NEC? Toggle switches can be grounded to the metal box by nothing more than 2-6/32 screws and they're mounted to the drywall too.

As I read the OP question, part of what is asked is "Can the box be bonded to the branch circuit EGC by only connecting the EGC to the Luminaire EGC. . .?"

So, in your example of the toggle, that's asking if the switch box can be bonded by landing the EGC to the yoke screw, and nowhere else.

 

[al hildenbrand]

When it is a metal box I don't use the green screw on the mounting bracket for anything. I do connect the light fixture to the egc.

same here.

For me, it depends upon the Luminaire. With a pendant, with a luminaire EGC coming up the chain, and a metal canopy without an EGC pigtail, I'll bond to the mounting bracket (for the exposed metal on the canopy) and leave enough extra to wirenut to the pendant EGC. And, to say it again, the metal box gets bonded to the branch circuit EGC before anything else by bringing the wire around a box ground screw, or under a ground clip with as long a tail for the luminaire bonds as practical.

 

[kwired]

For me, it depends upon the Luminaire. With a pendant, with a luminaire EGC coming up the chain, and a metal canopy without an EGC pigtail, I'll bond to the mounting bracket (for the exposed metal on the canopy) and leave enough extra to wirenut to the pendant EGC. And, to say it again, the metal box gets bonded to the branch circuit EGC before anything else by bringing the wire around a box ground screw, or under a ground clip with as long a tail for the luminaire bonds as practical.

My installs vary as well depending on conditions. Metal boxes always get a bonding screw - if there are EGC's entering via raceways or cables. If raceway or cable is the qualifying ECG with no other wire EGC's then all there is to deal with is any EGC of the luminaire. If Luminaire has metal bracket securely bolted to an already bonded outlet box, I almost never connect anything to the bonding screw on the bracket except maybe the luminaire EGC pigtail.