Sub Panel Grounding and Bonding NEC Code


So, I think I understand this correctly; however, I want some feedback.

Please, see the attached pictures of the sub-panel.

In this condo, there is a 200A main breaker/disconnect outside of the dwelling that feeds this sub-panel. Note that there are only the 3 conductors coming in 2 hot, 1 neutral.

I firmly believe that there should be a 4th conductor that is only a ground that should be grounded to the green screw side of the panel, and that only ground wires should be located on that bus. However, I’ve only been a home inspector for about a year and I’m arguing with a GC.

Can someone with a bit more electrical experience please comment? Should there only be ground wires on the right side? Should there be a ground conductor attached to the green screw side? Should the green screw be screwed into the panel enclosure?

I think the answer should be yes to all of the above, but I want to be sure.

The feeder to this panel should be an SER cable (not SEU) which is 4 conductors. The neutrals and EGC’s must be separate.

Yes to all.

After looking closer I believe a grounding bus bar needs to be installed for the grounds and the green screw removed.

Yes remove the screw and install separate ground bus.

I agree, there are some panels where the jumper between the bus bars on the left and right can be removed to create two distinct bus bars (neutral and EGC). This panel does not appear to be one of those types so a separate EGC bus bar needs to be installed and all of the EGC’s moved to that bar.

With a 3 wire feed the bond screw needs to be installed to allow the breaker to trip.

Without the bonding screw the enclosure would not be grounded so connecting the EGC’s to it would mean that they are floating as you’ve suggested. Currently the circuit breakers would function normally because the EGC’s are connected to the neutral bus.

As mentioned the cable needs to be changed to a 4 conductor, green screwed removed and the additional EGC bus can be installed.

Here is why polls are bad. You have two votes (1) yes and (1) no. This is what bothers someone like me because this is a very important issue that is right now going 50/50 on the votes. If inspectors are 100% certain then at this point the vote would be very clear.

Except for meeting the exception in 250.32(B) you will always need to ensure you have a separate “floating” bus for the grounded (neutral) and enclosure bonded bus for the equipment grounding conductors and subsequent GEC, which will make a connection to the equipment grounding bus.

I do like the statement said by Jim which is very astute in that if an existing installation exists, which you HI’s may see, and a 3 wire setup was installed to the detached building or structures remote panel that without connecting the grounded/grounding conductor to the panel enclosure (bonding) you may never trip an OCPD. Just remember that is in existing applications only as all other applications require 4 conductors unless of course its only a single branch circuit and no panel which is a whole different lesson or topic in itself.

Long story short…I don’t like seeing a 50/50 split on a POLL as it tells me the education is weak. But thats ok…ask your questions and LEARN but Polls…ehhhh…don’t like em.

Hey Paul, Do you know when the code changed that sub panels need a ground wire (4wire) and the ground/neutral wire be separated? I always will recommend updating to current code for safety but need to know if its improper grounding on the 4point reports. If its grandfathered then its should not be a defect on a 4point right?

Is the sub-panel in the same structure or a separate structure? If it’s a separate structure the NEC exception that allowed you to bond the neutral was removed in the 2008 NEC. If the sub-panel is within the same structure they have always been required to be separate, at least for the past 100 years. :sunglasses:

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Interesting, There has to be a ground rod if they are bonded at a detached structure right?
They are same structure, house sub panel and ac sub panel. For more info, I just posted in the emergency forum. Thank you for the response Robert!

A detached structure with a panel fed by a feeder always requires a grounding electrode system, could be two ground rods. Prior to the 2008 NEC that feeder could be 3-wire with the neutral bonded, 2008 and post 2008 code cycles a 4-wire feeder is required. A sub-panel in the same structure requires only a 4-wire feeder and the neutrals and EGC’s isolated.

This could be perfectly safe! What paralleled paths are you concerned about?

Why would you argue with a GC? Give your client your opinion and move on.