480v grounded 3 phase serving an oil well pump jack

[amerijet]

I am located in a state that has adopted UEC however it is only licensed and inspected by cities that require it. Hence the problem. I have seen older oil wells that have a 3 wire grounded phase 480 to ground reference on two legs and 0 on the other phase usually B phase.
I have no fourth wire coming as a low impedance circuit to the main disconnect at the utility pole hence the ECG is only tied to the grounding rods.
I have talked with inspectors in the cities, power companies and other electricians and don't really get any feedback on this subject. I ve milled through NEC and feel 4th wire or changing to single phase is the only real option here to protect myself and others. Any feedback on this would be extremely helpful!

 

[retirede]

Protect from what? As long as you have (properly installed) overcurrent protection at the well, it’s not unsafe. It’s just like the 3 wire service entrance to your house.

 

[don_resqcapt19]

Yes, after the main disconnect, an EGC is required. If one of the ungrounded conductors would fault to any metal part, you would have 480 volts from that part to the earth. There is no fault clearing path.
The grounding electrodes should be at the service disconnect connected to the grounded circuit conductor, and the EGC originates at that point.
Are the circuit conductors between the service disconnect and the equipment in metal conduit? If so, the metal conduit would be the EGC.

 

[winnie]

Please clarify: is the EGC only tied to grounding rods, or is the EGC tied to both grounding rods and the Grounded Conductor from the utility? Is this supposed to be an ungrounded system that happens to have a fault, or is this supposed to be a corner grounded delta?

If the EGC is properly bonded to the grounded conductor, then you have a low impedance circuit for fault current. This is exactly how most utility service drops work; you have a single grounded circuit conductor that also functions as the fault current return path from the utility to the service, then at the service you have the EGC (and ground rods) connected to the grounded circuit conductor, and from the service onwards you have separate grounded circuit conductors and EGCs. This is(was?) sometimes permitted for some feeders, and I'm not going into the specifics of when feeders are permitted without a separate EGC; the key point is that in these situations the EGCs are bonded to the grounded conductor.

Don't get tripped up by the fact that the grounded conductor might not be the neutral. It is still a conductor intentionally held at ground potential by connection to grounding electrodes and bonding to the EGCs.

A corner grounded delta system, where the EGCs are properly bonded to the grounded conductor has a perfectly fine fault current path.

Now: if you have a corner grounded delta system, and then have EGCs that are only connected to ground electrodes without the necessary bonding, then you do have a safety issue, one that needs to be fixed with proper bonding.

 

[amerijet]

Winnie thank you for your reply. Yes it is a corner grounded system as I know it. Leg A 496v to ground rods leg B 0v to ground rods leg C 496 to ground rods
The EGC is only to the ground rods which I feel is unsafe as I have seen two applications where the motor has shorted and not blown any of the fuses. One of the utility companies want a slug in the grounded phase so it doesn't blow fuses till you have a second phase to phase fault. Tying to EGC to the grounded phase just blows the fuses as it is considered a currant carrying conductor by one of the utility companies. Also wonder if a fault alarm is needed and if it would work as it could only be connected to the ground rods. Thank you for your help as I don't like the situation and it doesn't blow a fuse when there is a motor fault. Ground fault and turn to turn fault.

 

[infinity]

3 wire grounded phase 480 to ground reference on two legs and 0 on the other phase usually B phase.
I have no fourth wire coming as a low impedance circuit to the main disconnect at the utility pole hence the ECG is only tied to the grounding rods.

So at the service disconnect one of the phases is bonded to the metal enclosure?

 

[kwired]

You still have to bond that grounded conductor at the service equipment and run separate EGC beyond the service equipment just like you do with a grounded neutral conductor on systems that have one of those. In both cases it creates a low impedance path back to the source to help facilitate overcurrent protection at clearing ground faults when they occur. This source has no neutral you can ground any ONE of the conductors to create a grounded system.

 

[winnie]

Winnie thank you for your reply. Yes it is a corner grounded system as I know it. Leg A 496v to ground rods leg B 0v to ground rods leg C 496 to ground rods
The EGC is only to the ground rods which I feel is unsafe as I have seen two applications where the motor has shorted and not blown any of the fuses.

If the EGC only goes to the ground rods but is not bonded to the grounded conductor, that is _very_ unsafe. A fault to from hot to EGC will energize the EGC without tripping breakers.

Note that a motor can short internally and the motor winding will limit current flow so that you wouldn't blow fuses; so you the fact that you've seen motor failures without fuses blowing doesn't say much one way or the other about your overcurrent protection.

One of the utility companies want a slug in the grounded phase so it doesn't blow fuses till you have a second phase to phase fault.

You _don't_ want a fuse in the grounded phase. Just like not having a switch on the neutral; when the circuit opens you want everything downstream of the switch the be at ground potential, not energized at 480V.

Tying to EGC to the grounded phase just blows the fuses as it is considered a currant carrying conductor by one of the utility companies.

Current carrying conductor or not shouldn't matter. You _should_ be able to connect the grounded phase to the EGC. If this causes high current flow or blows fuses, then you have something else going on that is causing the problem. The voltage between EGC and grounded conductor should be low, and when you connect the two very little current should flow.

Also wonder if a fault alarm is needed and if it would work as it could only be connected to the ground rods. Thank you for your help as I don't like the situation and it doesn't blow a fuse when there is a motor fault. Ground fault and turn to turn fault.

Maybe try drawing out the entire system, from the utility transformers with their grounding, to the service, feeder, motor, EGCs, ground rods, etc. That might help clarify what you actually have going on.

IMHO it still isn't clear to me if you are _supposed_ to have a corner grounded system, or if you are supposed to have an ungrounded system but have a persistent ground fault that makes it look corner grounded.