New Electrical Service, No Neutral

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hbendillo

Senior Member
Location
South carolina
Our company received a telephone call from the owner to resolve some issues brought up by the electrical inspector regarding the electrical service for one of our projects. I was not involved in the original design for the project but after review of the drawings and speaking with the power company we have the following:

A new three-phase 480-volt electrical service was added for the building. The existing service, 208-volt three-phase, remains. The new service was added to feed two new elevators added to the building.

Service Drop: Overhead service drop from a pole mounted, open delta, transformer bank; 3-#1/0 with messenger/neutral cable. Messenger cable tied off to the building and the three phase conductors brought down to the meter through service head and conduit. So no neutral to the service equipment.

New Service: Meter and 200 amp service rated disconnect on outside wall. Conductors from meter to disconnect and then inside to wiring trough in main electrical room: 3-#3/0 & #6 G.

Inspector thinks the ground wire should be a #4.

My take is that the grounding electrode conductor should be sized #4 (These are all copper wire sizes), for meter and service disconnect. Anything past the service disconnect should be sized according to 250-66 which would be #6. The ground wire from the meter to the service disconnect should probably be #4.

This service is strictly providing the three-phase circuits for the two elevators and nothing else.

I have never designed an electrical service to a commercial building without a neutral. I'd like some opinions on the setup for the service and any other issues that I may be overlooking.
 

jumper

Senior Member
Pretty sure that neutral has gotta land in the service equipment.

250.24(C) Grounded Conductor Brought to Service Equipment.
Where an ac system operating at less than 1000 volts
is grounded at any point, the grounded conductor(s) shall
be routed with the ungrounded conductors to 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).
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
...... 3-#1/0 with messenger/neutral cable. Messenger cable tied off to the building and the three phase conductors brought down to the meter through service head and conduit. So no neutral to the service equipment


If i picture this correctly, the messenger wire that MAY or MAY NOT be the grounded conductor is stopped at the building and is NOT terminated in the equipment?

So if there is a fault on the equipment how does it go back to the source?
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Our company received a telephone call from the owner to resolve some issues brought up by the electrical inspector regarding the electrical service for one of our projects. I was not involved in the original design for the project but after review of the drawings and speaking with the power company we have the following:

A new three-phase 480-volt electrical service was added for the building. The existing service, 208-volt three-phase, remains. The new service was added to feed two new elevators added to the building.

Service Drop: Overhead service drop from a pole mounted, open delta, transformer bank; 3-#1/0 with messenger/neutral cable. Messenger cable tied off to the building and the three phase conductors brought down to the meter through service head and conduit. So no neutral to the service equipment.

New Service: Meter and 200 amp service rated disconnect on outside wall. Conductors from meter to disconnect and then inside to wiring trough in main electrical room: 3-#3/0 & #6 G.

Inspector thinks the ground wire should be a #4.

My take is that the grounding electrode conductor should be sized #4 (These are all copper wire sizes), for meter and service disconnect. Anything past the service disconnect should be sized according to 250-66 which would be #6. The ground wire from the meter to the service disconnect should probably be #4.

This service is strictly providing the three-phase circuits for the two elevators and nothing else.

I have never designed an electrical service to a commercial building without a neutral. I'd like some opinions on the setup for the service and any other issues that I may be overlooking.

250.24(C) requires the neutral to be brought to the service disconnecting means when supplied by a grounded system. Of course all other requirements also apply such as MBJ, GES, etc. Be advised that the lack of the neutral as you describe is no trivial matter and has serious safety consequences.
 

iwire

Moderator
Staff member
Location
Massachusetts
To get right to the point, what is the intended ground-fault path without a neutral being bonded to the service gear?
 

hbendillo

Senior Member
Location
South carolina
Pretty sure that neutral has gotta land in the service equipment.

250.24(C) Grounded Conductor Brought to Service Equipment.
Where an ac system operating at less than 1000 volts
is grounded at any point, the grounded conductor(s) shall
be routed with the ungrounded conductors to 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).

If I am looking at this correctly, the system in question is not "grounded" at any point.
 

hbendillo

Senior Member
Location
South carolina
To get right to the point, what is the intended ground-fault path without a neutral being bonded to the service gear?

That is my problem with this service. How does a ground fault generate enough current to properly operate the overcurrent devices? Through the ground back to the substation?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
And if it truly is not grounded at any point, not even in the POCO side, then you must supply a ground detector.
I would be very surprised if the elevator equipment allows use of an ungrounded delta though.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
If I am looking at this correctly, the system in question is not "grounded" at any point.
You either have to ask the utility that question or you have to look at the utility transformer secondary connections, assuming pole mount transformers, and see if it is a grounded system.
Note that if the system is an ungrounded system there are additional code rules that will have to be complied with, one of which, the requirement for ground detectors, has already been stated. A second would be that the breakers on this service would have to straight rated at 480 volts. Breakers rated 480/277 would not be permitted.
 
Last edited:

hbendillo

Senior Member
Location
South carolina
Thanks for the replies. I need to go through the drawings again. I am surprised the power company would drop a service to a commercial building without a neutral.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
That is my problem with this service. How does a ground fault generate enough current to properly operate the overcurrent devices? Through the ground back to the substation?

Hence one of the main reasons for 250.24(C). It would be extremely unlikely that the POCO 480 service is anything other than a 480Y in this day age. If so, the only way to make this compliant and safe is to comply with 250.24(C) and other applicable rules even if you have no load on the neutral.
Now others may jump in here a say that maybe it is a corner grounded or ungrounded service but I would be very surprised if any POCO, except in very rare cases, would furnish anything but a 480Y. And even if you had an ungrounded or corner grounded source that would bring on a whole 'nother bunch of code requirements.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
It was intended to be a 480-volt three-phase service, not 480/277. According to the power company it is an ungrounded delta.

If they insist it is a delta service, it would likely not be ungrounded in my experience. This could be setup as a 480/240 delta with the center of one winding grounded. You would then have a high leg of 416 volts to ground/neutral but that would still be a grounded system. I've in rare cases seen a POCO do this if they have no other option due to having only 2 phases and the neutral available on a Y primary system.
 

hbendillo

Senior Member
Location
South carolina
If they insist it is a delta service, it would likely not be ungrounded in my experience. This could be setup as a 480/240 delta with the center of one winding grounded. You would then have a high leg of 416 volts to ground/neutral but that would still be a grounded system. I've in rare cases seen a POCO do this if they have no other option due to having only 2 phases and the neutral available on a Y primary system.

I guess I need to write a letter to the POCO to get them to confirm. But I specifically asked if they had a corner grounded delta or center winding grounded delta service. He said no. I too am surprised that no neutral was provided for the service.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
And I would immediately check with the elevator contractor to see whether ungrounded delta is acceptable.
You might need to install a transformer (bank) just to provide a center ground or else make the system corner ground on your own. POCO would not need to be involved in that, except that there would be no alternate return path if the conductor that you grounded became interrupted on the POCO side.
 
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