NEC Metal Box Grounding

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timm333

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Minneapolis, MN
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Electrical Design Engineer
I have a question regarding the grounding of metal boxes for lighting fixtures. Each light fixture has its own metal box, so if there are 10 lighting fixtures in a circuit, there would be 10 metal boxes. The EGC conductor of this circuit would be connected to each of these metal boxes in accordance with section 250.148 (C) of NEC. Also this EGC would be connected to ground in the lighting panel.

Is it better to connect some of these metal boxes directly to the grounding electrode, or is it enough to just connect the EGC to ground in the lighting panel? Thanks
 
timm333 said:
I have a question regarding the grounding of metal boxes for lighting fixtures. Each light fixture has its own metal box, so if there are 10 lighting fixtures in a circuit, there would be 10 metal boxes. The EGC conductor of this circuit would be connected to each of these metal boxes in accordance with section 250.148 (C) of NEC. Also this EGC would be connected to ground in the lighting panel.

Is it better to connect some of these metal boxes directly to the grounding electrode, or is it enough to just connect the EGC to ground in the lighting panel? Thanks
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They should all be connected to the equipment grounding conductor at the lighting panel where the circuit supplying the lights originates!
 
In addition to connecting the EGC to ground in the lighting panel: if we also connect some metal boxes directly to grounding electrode, then will it be technically acceptable?
 
timm333 said:
In addition to connecting the EGC to ground in the lighting panel: if we also connect some metal boxes directly to grounding electrode, then will it be technically acceptable?
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You can connect them also to the GE by why would you want to do that?

And please update your profile to indicate your occupation.
 
A contractor wanted to connect the boxes to GE because he thought that it would increase reliability. But I think it is not necessary.
 
timm333 said:
A contractor wanted to connect the boxes to GE because he thought that it would increase reliability. But I think it is not necessary.
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I agree with you and Hal. Doing so would make it would appear as if the contractor had no clue which is evident by their question.
 
Only connect to the GE if it’s a time and materials job. If you understood grounding you would understand why a connection to the GE is not needed.
 
There will be a lot of replies to your question on connection to the GE. There is a lot of misunderstanding about grounding, don’t take the replies personally, but use to further your knowledge of the NEC
 
timm333 said:
In addition to connecting the EGC to ground in the lighting panel: if we also connect some metal boxes directly to grounding electrode, then will it be technically acceptable?
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It is technically acceptable, because the code allows it. This is because due to many people believing in myths about grounding, some manufacturers may still tell you to install electrodes to their equipment. So to avoid a conflict with those instructions, the code allows such 'auxiliary' electrodes. However they are almost always a waste and in some cases may actually be harmful.

Mike Holt explains this in the course this video from a few years ago, in which he discusses a grounding requirement for solar arrays that has since been removed from the NEC.

 
timm333 said:
I have a question regarding the grounding of metal boxes for lighting fixtures. Each light fixture has its own metal box, so if there are 10 lighting fixtures in a circuit, there would be 10 metal boxes. The EGC conductor of this circuit would be connected to each of these metal boxes in accordance with section 250.148 (C) of NEC. Also this EGC would be connected to ground in the lighting panel.

Is it better to connect some of these metal boxes directly to the grounding electrode, or is it enough to just connect the EGC to ground in the lighting panel? Thanks
Click to expand...
The equipment grounding conductor is a part of the effective ground fault clearing path. That path is the ungrounded conductor faulting to a metal part, the metal part connected to the EGC, the equipment grounding conductor connected to the equipment grounding terminal bar at the source panel, the equipment ground bar connected to the service neutral by the main bonding jumper, and the service neutral connecting to the utility transformer neutral terminal. Note that the grounding electrode is not a part of the effective ground fault clearing path. The equipment must always be connected to the EGC and not to the grounding electrode.

A connection to the grounding electrode will provide a fault clearing path, but since the physical path would be remote from the ungrounded circuit conductors, the impedance of that path will be substantially greater than that of the code required equipment grounding conductor.
 
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