primary overhead distribution no ground

mjmike

Senior Member
We are working on a project where the Utility delivers primary voltage to a complex via overhead. Then hits a couple utility transformer banks and normal 480V service entrances. One phase of the primary line (7200v L-G) however also hits an aerial cutout then continues on overhead for about a mile where it hits a pole mounted 10KVA 120/240v transformer. This aerial phase in question is metered at the cutout and the aerial distribution is owned by the owner the rest of the way (the 1 mile). Off this transformer are a couple small buildings. Our project involves upgrading one of the building meaning we will need to maybe change the transformer.

My question is, the service should end at the cutout where the meter is and that is where the ground should be established I would think, correct? However, there is no ground operated service disconnect per say. At the building we are upgrading, we should take to the transformer the 2 phases, the ground , and the neutral, correct? However the primary aerial distribution does not appear to be set up this way. It appears to be set up like a utility owned system where we would take the 2 phases and the neutral to the 10KVA transformer and establish the ground at the building we are working on.

Just trying to make some sense of all this. The Utility company is a co-op. They had asked the Owner to take over the primary line in question, but the Owner does not want to hand it over.
 

Smart $

Esteemed Member
Location
Ohio
Where is the service point? It sounds like it's at the cutout, but have to specific to give proper recommendations.

Anyway, unless the mile run to the 120/240 transformer is SWER (single wire earth return), the primary should already be grounded via the MGN (multi-grounded neutral).

Definitely run 2 ungrounded and neutral to the 120/240 transformer. Whether or not you have to run a grounding conductor somewhat depends on what Code cycle you are under.
 

mjmike

Senior Member
Where is the service point? It sounds like it's at the cutout, but have to specific to give proper recommendations.

Anyway, unless the mile run to the 120/240 transformer is SWER (single wire earth return), the primary should already be grounded via the MGN (multi-grounded neutral).

Definitely run 2 ungrounded and neutral to the 120/240 transformer. Whether or not you have to run a grounding conductor somewhat depends on what Code cycle you are under.
This is where part of my confusion is. I am thinking the cutout is the service point because that is where the meter is and where the utility stops. Anything beyond the cutout the utility stated they don't have anything to do with. However, if the cutout is the "service disconnect" it definitely is not accessible. The primary phase is a 1/0 ASCR. Speaking to the original installer, they indicated the cutout is a change of ownership point and not the service point.
 
Last edited:

Ingenieur

Senior Member
Location
Earth
We are working on a project where the Utility delivers primary voltage to a complex via overhead. Then hits a couple utility transformer banks and normal 480V service entrances. One phase of the primary line (7200v L-G) however also hits an aerial cutout then continues on overhead for about a mile where it hits a pole mounted 10KVA 120/240v transformer. This aerial phase in question is metered at the cutout and the aerial distribution is owned by the owner the rest of the way (the 1 mile). Off this transformer are a couple small buildings. Our project involves upgrading one of the building meaning we will need to maybe change the transformer.

My question is, the service should end at the cutout where the meter is and that is where the ground should be established I would think, correct? However, there is no ground operated service disconnect per say. At the building we are upgrading, we should take to the transformer the 2 phases, the ground , and the neutral, correct? However the primary aerial distribution does not appear to be set up this way. It appears to be set up like a utility owned system where we would take the 2 phases and the neutral to the 10KVA transformer and establish the ground at the building we are working on.

Just trying to make some sense of all this. The Utility company is a co-op. They had asked the Owner to take over the primary line in question, but the Owner does not want to hand it over.
there is only 1 conductor run to the 10 kva xfmr?
current carrying on insulators?
but no ground?

how is it hooked up?
at the xfmr
7200 low side connected to the 120/240 center tap/neut/gnd?
 

fmtjfw

Senior Member
readily accessible?

readily accessible?

Is the cutout any less accessible than equivalent cutouts at that voltage. I would consider a cutout on a 7200V line accessible if a telescoping hotstick could reach it from the ground.

If you need a handle at ground level, you should price out the cost of gang switch over that of several fused cutouts. I've also seen that the reliability of unmaintained gang switches to be much less that that of simple cutouts.

See 230 Part VIII Services Exceeding 1000 Volts, Nominal. 230.204(B) Fuses as Isolating Switch; 230.205 (A) "... service disconnect shall be permitted to be located in a location that is not readily accessible, if the disconnecting means can be operated by mechanical linkages from a readily accessible point or electronically ..."
 
Last edited:

mjmike

Senior Member
there is only 1 conductor run to the 10 kva xfmr?
current carrying on insulators?
but no ground?

how is it hooked up?
at the xfmr
7200 low side connected to the 120/240 center tap/neut/gnd?
Not sure how the transformer is wired, but yes, 1 phase on insulators and the grounded conductor.
 

mjmike

Senior Member
Is the cutout any less accessible than equivalent cutouts at that voltage. I would consider a cutout on a 7200V line accessible if a telescoping hotstick could reach it from the ground.

If you need a handle at ground level, you should price out the cost of gang switch over that of several fused cutouts. I've also seen that the reliability of unmaintained gang switches to be much less that that of simple cutouts.

See 230 Part VIII Services Exceeding 1000 Volts, Nominal. 230.204(B) Fuses as Isolating Switch; 230.205 (A) "... service disconnect shall be permitted to be located in a location that is not readily accessible, if the disconnecting means can be operated by mechanical linkages from a readily accessible point or electronically ..."
The cutout is accessible with a hot stick I would assume. I still don't understand though about the grounding. If the cutout is the service disconnect, then that is where the N-G bond should occur then the overhead should have a phase and a ground. I guess the key point he installer noted is it is a point of ownership change and not a service point.
 

GoldDigger

Moderator
Staff member
This is where part of my confusion is. I am thinking the cutout is the service point because that is where the meter is and where the utility stops. Anything beyond the cutout the utility stated they don't have anything to do with. However, if the cutout is the "service disconnect" it definitely is not accessible. The primary phase is a 1/0 ASCR. Speaking to the original installer, they indicated the cutout is a change of ownership point and not the service point.
1. The service point is not (necessarily) at the service disconnect. (And for a disconnect to be a service disconnect, there must be OCPD at it or very close to it.)
2. The service point is the nominal boundary between NEC and NEST jurisdiction. It may not correspond to installation or ownership of the equipment and conductors.
3. Basically, the service point is where POCO says it is, and that will vary from CO to CO.
4. The service disconnect is the boundary between service conductors and feeder or branch conductors.
 

Smart $

Esteemed Member
Location
Ohio
This is where part of my confusion is. I am thinking the cutout is the service point because that is where the meter is and where the utility stops. Anything beyond the cutout the utility stated they don't have anything to do with. However, if the cutout is the "service disconnect" it definitely is not accessible. The primary phase is a 1/0 ASCR. Speaking to the original installer, they indicated the cutout is a change of ownership point and not the service point.
Well someone has to know where the service point is...!!! It is usually where ownership changes from utility to consumer... but not always. Anyway, the service doesn't necessarily end at the service point, but you can't have a non-service transformer on the utility side of a service disconnecting means (SDM). So either the cutout is the SDM, or the service point is on the secondary side of the 120/240 transformer.

If there's only one wire running the mile to the transformer, then it's an SWER primary. Rather uncommon nowadays AFAIK. I'd have to look it up to see if it is permitted under NEC purview, but I don't believe it is.

BTW, what fmtjfw said regarding the cutout/SDM...
 

Bugman1400

Senior Member
Location
Charlotte, NC
Is there a reason why you wouldn't add the neutral for the 1 mile section to the xfmr? I'm not sure I'd trust the earth return from a couple of grounding rods to stabilize the L-N voltage. Not sure where the application is but, sandy or rocky soil could be a problem.
 

GoldDigger

Moderator
Staff member
Is there a reason why you wouldn't add the neutral for the 1 mile section to the xfmr? I'm not sure I'd trust the earth return from a couple of grounding rods to stabilize the L-N voltage. Not sure where the application is but, sandy or rocky soil could be a problem.
With a nominal voltage of 7200V, the voltage offset caused by earth electrode resistance may not be large enough to worry about. Once you get past the two electrode to earth resistances, the resistance through the earth itself will be too low to measure regardless of the soil type in between.
So look at the current on the distribution voltage line and the resistance of the two earth electrodes. For 10A of primary current a 25 ohm resistance will only cause a voltage offset of 250V out 7200.
But that 250V of touch or step potential in the earth around the electrodes could be real hazard, and you need to isolate (such as by distance) the primary earth electrode from any earth ground of the secondary voltage system.
 

iwire

Moderator
Staff member
Location
Massachusetts
Is there a reason why you wouldn't add the neutral for the 1 mile section to the xfmr? I'm not sure I'd trust the earth return from a couple of grounding rods to stabilize the L-N voltage. Not sure where the application is but, sandy or rocky soil could be a problem.
Not sure how the transformer is wired, but yes, 1 phase on insulators and the grounded conductor.
It seems there are two conductors.
 

mivey

Senior Member
My question is, the service should end at the cutout where the meter is and that is where the ground should be established I would think, correct?
That is the utility service point but really has little to do with the 120/240 volt system. The POCO is just not going to be responsible for owning or operating the 7200 line. The owner needs qualified operators or contractors for the 7200 equipment.

The 120/240 service to the building is a separate issue and different from the utility's "service point".

However, there is no ground operated service disconnect per say. At the building we are upgrading, we should take to the transformer the 2 phases, the ground , and the neutral, correct?
We could way over-complicate this but just take the 2 phases and grounded conductor to the pole (3 wires). Split the grounded conductor and equipment ground at the service disconnect for the building (outside disconnect or at inside main panel where 120/240 service conductor enters building).

In other words, treat it the same as you would if the utility owned the 7200 pole & transformer.

However the primary aerial distribution does not appear to be set up this way. It appears to be set up like a utility owned system where we would take the 2 phases and the neutral to the 10KVA transformer and establish the ground at the building we are working on.
That would be my recommendation.

Just trying to make some sense of all this. The Utility company is a co-op. They had asked the Owner to take over the primary line in question, but the Owner does not want to hand it over.
If the owner wants to be 7200 volt system operators then that's great. According to Captain Obvious, circumstances would dictate the best choice.
 
Top