MV Service Entrance Grounded Conductor

[mull982]

I'm looking at a new installation where a 500MCM 34.5kV SE feeder will be fed from an existing OH 34.5kV utility line to a new MV Switchgear lineup. The riser pole where the connection will be made will have a gang switch. The gang switch serves as the point of demarcation between utility and owner with cable after the switch belonging to owner.

The 34.5kV OH line appears to have a shield wire which is connected to a solid copper ground wire at each of the poles which runs down the pole to ground.

There is an existing riser pole on the site and it appears that there are only (3) phase conductors coming up the riser pole and no grounded conductor. The shields at each of the cable terminations are all connected to the ground wire running up the pole.

My question is in this type of SE application if the grounded conductor is required? Since there is nowhere on the pole or OH line to connect the grounded conductor to I'm assuming that is is not required and that only the cable shield is connected to ground points at both the riser pole and switchgear?

 

[JoeStillman]

Utilities ground the neutral all over the place. That's why the shields are sometimes called concentric neutrals. If you have concentric neutral cable, the outer wires are the grounded conductor.

 

[electrofelon]

Utilities ground the neutral all over the place. That's why the shields are sometimes called concentric neutrals. If you have concentric neutral cable, the outer wires are the grounded conductor.

But it sounds like the utility did not run a primary neutral to the service point. Maybe it's not an MGN system?

250.186(B) seems to address this but it hard to make sense of what they are trying to say.

 

[Julius Right]

As per NEC Art.310 E All metallic insulation shields shall be connected to a grounding electrode conductor, a grounding busbar, an equipment grounding conductor, or a grounding electrode.
You may use for cable insulation shield grounding a grounding electrode only. If it is about short length of cable, a single point grounding will be enough.

 

[JoeStillman]

@mull982 Is it a tape shield or concentric neutral cable? If the source is grounded wye, I would think that the utility company has a neutral wire (which may be what looks like a ground on your overhead system). Are they requiring your transformer to have a grounded wye primary? My local POCO does. I think it's because the fuses can then be rated for the L-N voltage.

 

[electrofelon]

If the source is grounded wye, I would think that the utility company has a neutral wire (which may be what looks like a ground on your overhead system).

I would think so too..... But this has come up before where, if we are getting the correct story, it seems it's an mgn distribution system but utility didn't supply the neutral. So the customer could use a Delta ->wye transformer, but it is a bit unclear to me if this would be NEC compliant.