I would like to get some more info on this. I’m not sure I’ve heard that before. Are you saying the bonding screw is not a good enough connection? I feel like in a service panel, the GEC is often only connected to the enclosure through the bonding screw.
Yes you are correct, the neutral and EGC (equipment grounding conductor) bus setup is backwards as other have stated. Since you have the correct 4-wire feeder to the detached structure the panel should be wired like a regular sub-panel, EGC’s connected to the bus which is connected directly to the enclosure (the one on the left) and the neutrals are connected to the bus that is isolated from the enclosure (the one on the right).
One other difference from a regular sub-panel is that since this is a separate structure a connection to a GES (grounding electrode system) is required. That would be via a GEC which gets connected to the EGC bus not the neutral bus.
All of the other sub-panels within the separate structure would require 4-wire feeders as well with the neutrals being isolated from the enclosures.
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@rmeier2 are you saying that the GEC DOES NOT need to
I too have not heard of what @dhorton2 mentioned and am curious about that.
Yes, if the GEC is connected to the panel, then it must be connected to the Ground bus (as robert just mentioned)
It cannot be connected to the neutral bus, because this would require bonding to be done through a screw, then through the enclosure, and then back to the GEC.
It needs to be connected to the grounding bus, so that it has a direct path to the GEC, without the enclosure acting as the connecting means…
I see that my first post was a little misleading… It can be connected to the ground bus, just not the neutral bus
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Thanks for the reply and clarification Robert! It’s much appreciated.
It’s a good question as to where the GEC needs to connect the system at a separate structure. As mentioned prior it cannot connect to the neutral. The code isn’t really clear as to whether or not it can connect directly to the metal enclosure. IMO it can because the metal enclosure can be used as part of the equipment grounding path. Also a sub-panel in a separate structure may not have an EGC bus if there are no wire type EGC’s.
Here’s the wording from the applicable code section.
250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) Grounding Electrode.
Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment
grounding conductor for grounding the normally non–current-carrying metal parts of equipment.
(B) Grounded Systems.
(1) Supplied by a Feeder or Branch Circuit. An equipment grounding conductor, as described in 250.118, shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
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Love having you on here Robert!
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Yes, I agree. That is, when you have separate ground and neutral buses anyway.
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As always happy to help. 