Grounded Conductor at the Service Disconect

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kenaslan

Senior Member
Location
Billings MT
I am trying to wrap my head around a recent violation an inspector had with an installation.

The main transformer is a 3 phase, 3 wire 14.4KV-480/277V Y-Y. This is for a 3phase 480V system. NO 277V. The inspector wanted both a GEC and a Grounded conductor run to the Service disconnect. Currently there are only the phase conductors and a Grounded Conductor. The Grounded Conductor is bonded to the service Disconnect and from there run to a ground rod.

Do 5 wires need to be run for the Service, or can we use 4?
 

Smart $

Esteemed Member
Location
Ohio
I am trying to wrap my head around a recent violation an inspector had with an installation.

The main transformer is a 3 phase, 3 wire 14.4KV-480/277V Y-Y. This is for a 3phase 480V system. NO 277V. The inspector wanted both a GEC and a Grounded conductor run to the Service disconnect. Currently there are only the phase conductors and a Grounded Conductor. The Grounded Conductor is bonded to the service Disconnect and from there run to a ground rod.

Do 5 wires need to be run for the Service, or can we use 4?
4 is all that is required... for a service. The grounded conductor is used for all bonding on the line side of the service disconnecting means.

For an SDS, still only 4 (3CCC + 1SSBJ) because the grounded conductor [neutral terminal] is not required to be run to the disconnecting means. However, the system bonding jumper and GES connection are required at the transformer when run this way.
 

Smart $

Esteemed Member
Location
Ohio
PS: There are some AHJ which interprets the grounding requirements as having to run a GEC from building to outside SDS transformer. I do not agree with that interpretation as long as the SSBJ is run and the transformer and building are considered two separate structures with each having its own GES.

Now if you don't have a separate GES at the SDS transformer, I can see why the inspector wants you to run a GEC.
 

kenaslan

Senior Member
Location
Billings MT
4 is all that is required... for a service. The grounded conductor is used for all bonding on the line side of the service disconnecting means.

For an SDS, still only 4 (3CCC + 1SSBJ) because the grounded conductor [neutral terminal] is not required to be run to the disconnecting means. However, the system bonding jumper and GES connection are required at the transformer when run this way.

But 250.24(C) Grounded Conductor Brought to Service Equipment.
Where an ac system operating at 1000 volts or less is
grounded at any point, the grounded conductor(s) shall be routed
with the ungrounded conductors t o each service disconnecting
means
and shall be connected to each disconnecting means
grounded conductor(s) terminal or bus. A main bonding jumper
shall connect the grounded conductor(s) to each service disconnecting
means enclosure. The grounded conductor(s) shall be
installed in accordance with 250.24(C)(1) through (C)(4).
 

Smart $

Esteemed Member
Location
Ohio
But 250.24(C) Grounded Conductor Brought to Service Equipment.
Where an ac system operating at 1000 volts or less is
grounded at any point, the grounded conductor(s) shall be routed
with the ungrounded conductors t o each service disconnecting
means
and shall be connected to each disconnecting means
grounded conductor(s) terminal or bus. A main bonding jumper
shall connect the grounded conductor(s) to each service disconnecting
means enclosure. The grounded conductor(s) shall be
installed in accordance with 250.24(C)(1) through (C)(4).
But what? Three ungrounded and one grounded make 4. A grounding conductor is not required for a grounded service... or rather the grounded conductor serves as the grounding conductor for the service.

I posted conductor info on running a feeder from an SDS transformer because that's what I think the AHJ is thinking and you are not. I do not know for a fact which you have, so I'm trying to cover both possibilities.
 

kenaslan

Senior Member
Location
Billings MT
Define SDS please.

We have Y-Y transformer. 2 meters, and three service disconnects. the system is a 480V three phase system, not a 480/277 system that is running a bunch of beam pumps in an oil field.

Yes, the simple solution is do what the AHJ wants and move on. However if it is not necessary another AHJ may allow it.

I see 3CCC and a GC to the disconnect. Then an EGC and a GEC with a bonding jumper and ground rod derived at each of the three service disconnecting means in the three locations.
 

Smart $

Esteemed Member
Location
Ohio
Define SDS please.

We have Y-Y transformer. 2 meters, and three service disconnects. the system is a 480V three phase system, not a 480/277 system that is running a bunch of beam pumps in an oil field.

Yes, the simple solution is do what the AHJ wants and move on. However if it is not necessary another AHJ may allow it.

I see 3CCC and a GC to the disconnect. Then an EGC and a GEC with a bonding jumper and ground rod derived at each of the three service disconnecting means in the three locations.
Rather than define SDS specifically, let's just say it is a transformer after the service disconnecting means and the run from the secondary terminals to the disconnecting means would be feeder conductors... not service conductors.

Do you or your party's representatives have access to a disconnecting means on the primary side of the transformer?
 

Smart $

Esteemed Member
Location
Ohio
...
I see 3CCC and a GC to the disconnect. ...
If you truly have a service run(s), a GC is not required, even if you have an ungrounded service. However, if it is an ungrounded service, i.e. no connection to X0, then you are required to have a ground fault detector installed.

See 250.24(A)(2) regarding the grounding of an outdoor transformer for service-supplied systems.
 
4 is all that is required... for a service. The grounded conductor is used for all bonding on the line side of the service disconnecting means.

I think this is dangerous.

4 wires: 3 hot and one GEC. what will provide a low impedance path back to the POCO's transformer for fault clearing? GEC is a long path to the transformer.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I think this is dangerous.

4 wires: 3 hot and one GEC. what will provide a low impedance path back to the POCO's transformer for fault clearing? GEC is a long path to the transformer.
No, it's three ungrounded conductors and one grounded conductor. The grounded conductor is the low impeadance path on the line side of a service. The grounding electrode system doesn't start until the load side of the service.
 
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