480v 3ph 4w service grounding and bonding beyond the disconnect

[BackCountry]

Gentlemen, this is confusing me and after reading each post on 250.30(a)(1) exception no. 2 I’m even more confused. Single line diagram is attached.

Scenario:

480v 3ph 4w service into a three pole fused disconnect. Neutral and GEC are bonded in the fused disconnect (service entrance) and the neutral stops there, nothing in this installation requires a neutral derived from the service (all 480v, no line to neutral 277v used). This is mounted to a wooden panel board at the property line.

From the fused disconnect, three 3/0 CU feeders (phase A and B, third conductor is at present bonded to ground and serves as an EGC) go underground 400’ to three 480x120/240 step down transformers, all on phase A and B, obviously not balanced. Those transformers all serve different buildings on this site, and have a neutral to case bond at the step down transformer. They also have ground rods bonded.

We will be installing a 480v 50kw generator between the service panel board and the step down transformers. We will also be installing a large PV array. As part of the project, we will balance the three step down transformers and restore phase C.

The million dollar question is:

Do I need an EGC from the service entrance to the step down transformers if there is no neutral anywhere used? I really don’t want to yank out those 3/0 CU feeders and repull an EGC, I’d love to take the third 3/0 conductor and make that phase C. I’m not real up on grounding a conductor and using it as an EGC, your help is appreciated.

 

[Barney B]

1. Your text and one-line disagree on where your neutral to ground bond is located. Most POCOs will not allow a grounding electrode conductor to be brought into their meter base. I don't know about PG&E.
2. If your grounded ("neutral") conductor from the POCO transformer ends at the meter base (as shown in the one-line), this violates 250.24(C), which requires that the grounded conductor be brought to the service disconnect.
3. An equipment grounding conductor sized according to Table 250.122 is required to be run with your feeders unless the raceway containing those feeder conductors qualifies as an EGC under 250.118.

 

[winnie]

Feeder conductors must have a separate EGC.

Service conductors can use the grounded conductor as both circuit conductor and EGC.

So I think that if you can use a corner grounded delta, and if the utility will reconfigure the service to be corner grounded and if you can move the location of the service equipment, then you might be able to turn that three wire feeder missing its EGC into a compliant service.

But I don't think this will be practical. Lots of equipment is unhappy with corner grounding. The utility probably doesn't want to change things. Straight 480V (rather than 480/277V) hardware is more expensive. Depending on usage at the meter location you might not be able to convert the feeder into service conductors.

I think you need to pull the EGC, and I'd suggest a minimum neutral as well.

Jon

 

[BackCountry]

1. Your text and one-line disagree on where your neutral to ground bond is located. Most POCOs will not allow a grounding electrode conductor to be brought into their meter base. I don't know about PG&E.
2. If your grounded ("neutral") conductor from the POCO transformer ends at the meter base (as shown in the one-line), this violates 250.24(C), which requires that the grounded conductor be brought to the service disconnect.
3. An equipment grounding conductor sized according to Table 250.122 is required to be run with your feeders unless the raceway containing those feeder conductors qualifies as an EGC under 250.118.

Hey Barney,

You're correct -- the SLD is not correct -- the neutral and GEC are located in the service disconnect, not in the meter can. The raceway is PVC since it's underground, so that's a no go. Dang.

 

[BackCountry]

Feeder conductors must have a separate EGC.

Service conductors can use the grounded conductor as both circuit conductor and EGC.

So I think that if you can use a corner grounded delta, and if the utility will reconfigure the service to be corner grounded and if you can move the location of the service equipment, then you might be able to turn that three wire feeder missing its EGC into a compliant service.

But I don't think this will be practical. Lots of equipment is unhappy with corner grounding. The utility probably doesn't want to change things. Straight 480V (rather than 480/277V) hardware is more expensive. Depending on usage at the meter location you might not be able to convert the feeder into service conductors.

I think you need to pull the EGC, and I'd suggest a minimum neutral as well.

Jon

You're correct, it would not be practical to reconfigure the service. My gut tells me that they started off with a single phase service, didn't run a ground, changed to 3ph 4w 480v to overcome voltage drop (those step downs are about 500' away total) and then just turned one wire into an EGC so they didn't have to pull anything else.

500' of 3/0 in 2" PVC is not going to be fun to pull out and repull, it's been in the ground for at least 10 years, might have to mandrel it even.