My warehouse is in an industrial complex. Our building has 6 units for 6 unique tenants. There is one meter room where all the meters are located as well as a 1600 amp main disconnect. Service comes in, goes through the disconnect and then feeds out to everyone's units.

The main service panel has three live wires entering—3 phase service—and a neutral. There is no ground wire coming in. On our panel the grounds are all mixed with neutrals except for one circuit is bonded to the panel separately. It appears the only actual "ground" is a 6/0 awg cable that runs from somewhere around the disconnect and through the building up to a steel column under the roof.

Is this proper?
Do any subpanels I install need to be grounded?
How about the bonded neutrals?

electrical panel

(disregard the bottom breaker, that was put in by the previous tenant and is clearly not to code)

  • All sub panels require bonding, grounding, and a grounded neutral if using for other than 3phase loads..
    – Kris
    Jul 30, 2018 at 12:06

1 Answer 1


Welcome to stack exchange. This site is usually for DIY residential owners, because when you get involved in commercial you usually will need a professional electrical contractor, but I will take a crack at your question.

First your ground attached to your first means of disconnect is the building ground. It can't be a 6/0 since there is no such gauge. It is probably a 3/0 or 4/0 depending on how it was originally sized. All other grounds from your tenant panels must be sized and connected to this ground. So yes all of your tenant services need a grounding conductor to the original ground.

Second on commercial properties, if you panel grounds are mixed with your neutrals they need to be separated and installed on proper buses. Neutrals need to be on a neutral bus and grounds need to be on the ground bus, and if the panel is the first means of disconnect the neutral bus must be bonded. If you have a separate main breaker or fused disconnect the neutral must be bonded there and the neutral bus in the panel and the ground bus must be isolated from each other.

Third NEC Article 250.50 states that all grounding methods available shall be bonded together to form a grounding electrode system. I can't say how many are available on your building but there should be at least two. One is the building steel you described and two would be a driven ground rod.

Conclusion - If what you described is factual; then no your grounding system is incorrect and needs to be repaired and brought up to code. I might add that proper grounding is important not only for safety purposes, but for the proper operation of your electrical system. I can almost grantee that your tenants will have problems with there electrical and electronic equipment, and if you call in someone to trouble shoot it. It will take longer to trace out and cost more to repair.

Still I recommend that you bring in a recommended and trust worthy commercial electrical contractor to get you an "eyes on" inspection and recommendation.

Good Luck.

  • Thanks for the in depth answer. Ill clarify further: i am a tenant in the building, not the owner :/...You said: neutrals to neutral bus and grounds to ground bus. Problem is there is no ground bus. It would appear that the panel itself is the ground since it is the only thing that is actually attached to the building ground (except the main neutral). Is it possible the contractors simply elected to use the panel or conduit as the main connection to ground? I looked around the whole building - there is not one other ground anywhere except the one I mentioned
    – Callesun
    Jul 31, 2018 at 2:45
  • @Callesun - In commercial buildings there is no code exception for using the neutral bus as a combined neutral and ground bus. That exception is for dwelling units only. You can purchase extra bus bars for any panel manufactured. So you need to properly install a ground bus and move the grounds off of the neutrals. Jul 31, 2018 at 12:43

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