No grounding conductor on three phase feed to building

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GOtto

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California, USA
I am working on a design to upgrade service switchgear and an MCC for a site that serves several well and booster pumps. The existing service to the site was originally a 480V ungrounded 3-phase delta service. As part of the upgrade the utility is upgrading their transformer to a 480Y/277V, grounded 4-wire wye service. All that is if fine and I understand what is needed to accomplish those upgrades, but my question is regarding some of the feeders to a couple remote well starter panels that are several hundred feet away. The pump starter panels are also being upgraded as part of this design.

The existing feeders to these well starter panels are direct buried 3-wire cables with no equipment ground conductor. Since there is not a conduit to potentially add a ground conductor I am trying to figure out the best approach to provide a safe and compliant system. The panels are located in a shed, so I am treating them as buildings whether or not that make much difference other than I am putting a mini power zone for lighting and SCADA control cabinet power . I am not finding much in the NEC that captures this scenario of a grounded system that has existing feeders without a grounded or ground conductor. Since the only load being served is a 3 phase motor, I do not need the neutral conductor in the feeder.

My questions:
1. Can I safely establish a ground at the well starter panel with a new grounding electrode system at the remote building?
2. Would I need a ground fault detector for the well strater panel to potentially shut trip either the breaker starter panel breaker or the feeder breaker at the main service?
3. Is the only code complaint installation to bring an equipment ground conductor from the main service to the shed? If this is the case, would I need to install a new feeder cables with the ground conductor, or could the ground conductor be a separate direct buried cable?

Thanks for the help, let me know if I need to clarify anything.
 
GOtto said:
I am working on a design to upgrade service switchgear and an MCC for a site that serves several well and booster pumps. The existing service to the site was originally a 480V ungrounded 3-phase delta service. As part of the upgrade the utility is upgrading their transformer to a 480Y/277V, grounded 4-wire wye service. All that is if fine and I understand what is needed to accomplish those upgrades, but my question is regarding some of the feeders to a couple remote well starter panels that are several hundred feet away. The pump starter panels are also being upgraded as part of this design.

The existing feeders to these well starter panels are direct buried 3-wire cables with no equipment ground conductor. Since there is not a conduit to potentially add a ground conductor I am trying to figure out the best approach to provide a safe and compliant system. The panels are located in a shed, so I am treating them as buildings whether or not that make much difference other than I am putting a mini power zone for lighting and SCADA control cabinet power . I am not finding much in the NEC that captures this scenario of a grounded system that has existing feeders without a grounded or ground conductor. Since the only load being served is a 3 phase motor, I do not need the neutral conductor in the feeder.

My questions:
1. Can I safely establish a ground at the well starter panel with a new grounding electrode system at the remote building?
2. Would I need a ground fault detector for the well strater panel to potentially shut trip either the breaker starter panel breaker or the feeder breaker at the main service?
3. Is the only code complaint installation to bring an equipment ground conductor from the main service to the shed? If this is the case, would I need to install a new feeder cables with the ground conductor, or could the ground conductor be a separate direct buried cable?

Thanks for the help, let me know if I need to clarify anything.
Click to expand...

I would think about the only option short of replacing the feeders is to convert them to single phase, use the remaining conductor as the EGC and either change the pumps to single phase or provide some type of single to three phase conversion equipment

Of course that is entirely dependent on the existing conductors being large enough to supply the needed ampacity at single phase.
 
iwire said:
I would think about the only option short of replacing the feeders is to convert them to single phase, use the remaining conductor as the EGC and either change the pumps to single phase or provide some type of single to three phase conversion equipment

Of course that is entirely dependent on the existing conductors being large enough to supply the needed ampacity at single phase.
Click to expand...

Single phase is not an option here, since we are dealing with 150HP and 200HP motors. Thanks.
 
tom baker said:
No because it was never allowed.
Click to expand...

The closest you will come is the allowance, at one time, to use the grounded conductor (often a neutral) as the EGC instead of running a separate EGC. Just like for the service entrance wiring.
No allowance, AFAIK, for not running either.
Otherwise if a ground fault developed at the POCO side (transformer, etc.) and a second fault developed at the customer side there would not be a metallic fault clearing path, just a ground rod at each end.
Since there was no ground detector on the ungrounded circuit that would not be an unforeseeable occurrence. Now that the utility is supplying a grounded wye, it is an even more likely scenario, and unacceptable.
 
GoldDigger said:
The closest you will come is the allowance, at one time, to use the grounded conductor (often a neutral) as the EGC instead of running a separate EGC. Just like for the service entrance wiring.
No allowance, AFAIK, for not running either.
Click to expand...

I agree and will add that the fact it was an ungrounded supply system did not change the requirement for an EGC.
 
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