I wanted to better understand requirements of 250.184 and 250.186 (2023 NEC) using the attached example of MV system. In this example the customer (distributed generation site) is interconnecting with 24.9kV utility distribution line which has a multipoint grounded neutral ran with distribution.
This neutral comes into the site as part of a concentric cable neutral with UG distribution feeders and then transition to an overhead ASCR type neutral as the UG feeders come up a riser pole and transition to overhead. I've illustrated on drawing where feeders and neutral transition from UG to OH cable for context.
I was hoping someone with familiarity with sections could help clarify a few questions:
1) In looking at 250.186 I would consider this service one with a grounded conductor (neutral) at service point and thus fall under requirements of 250.186(A). This section requires that this grounded conductor be installed and routed to the first service disconnect which in this case will be the switch, and the grounded conductor will be routed be connecting incoming cable concentric neutrals to OH ASCR neutral for routing to switch. This section requires that this grounded conductor to switches grounded conductor terminal or bus with a bonding jumper between the grounded conductor and enclosure. Given that a switch typically does not have a "grounded bus" or maybe not even a specific grounding point at all would we just carry the neutral over with a bonding jumper between OH neutral line and switch frame?
2) Since this neutral will be carried all the way to the transformer I would consider this a solidly grounded neutral system which falls under 250.184. Seeing that this is also a multi-grounded neutral system I would say that this would specifically fall under 250.184(C). If that is the case then after the neutral is initally bonded to first disconnect (switch) as described in #1 above would this neutral just be able to continue to run all the way to transformer wye point with bonding to ground along the way at locations required by 250.184(C) and shown on drawing? I'm assuming the cable concentric neutral would be allowed to serve as this neutral if its a 1/3 concentric neutral?
3) Is there technically a requirement for an Equipment Ground Conductor (EGC) between switch and recloser, and between recloser and transformer like there would be on an LV system after first disconnecting means? The multipoint grounding is throwing that off a bit for me. If required would the concentric neutral be able to double as both a neutral and EGC?
4) On the LV detla side of transformer what would the ground conductor between transformer and first disconnect means downstream be considered. To me these would be an EGC given that the neutral is derived by seperate grounding transformer. I'm used to LV application with wye secondary where SSBJ is ran between transformer and first disconnecting means downstream.
This neutral comes into the site as part of a concentric cable neutral with UG distribution feeders and then transition to an overhead ASCR type neutral as the UG feeders come up a riser pole and transition to overhead. I've illustrated on drawing where feeders and neutral transition from UG to OH cable for context.
I was hoping someone with familiarity with sections could help clarify a few questions:
1) In looking at 250.186 I would consider this service one with a grounded conductor (neutral) at service point and thus fall under requirements of 250.186(A). This section requires that this grounded conductor be installed and routed to the first service disconnect which in this case will be the switch, and the grounded conductor will be routed be connecting incoming cable concentric neutrals to OH ASCR neutral for routing to switch. This section requires that this grounded conductor to switches grounded conductor terminal or bus with a bonding jumper between the grounded conductor and enclosure. Given that a switch typically does not have a "grounded bus" or maybe not even a specific grounding point at all would we just carry the neutral over with a bonding jumper between OH neutral line and switch frame?
2) Since this neutral will be carried all the way to the transformer I would consider this a solidly grounded neutral system which falls under 250.184. Seeing that this is also a multi-grounded neutral system I would say that this would specifically fall under 250.184(C). If that is the case then after the neutral is initally bonded to first disconnect (switch) as described in #1 above would this neutral just be able to continue to run all the way to transformer wye point with bonding to ground along the way at locations required by 250.184(C) and shown on drawing? I'm assuming the cable concentric neutral would be allowed to serve as this neutral if its a 1/3 concentric neutral?
3) Is there technically a requirement for an Equipment Ground Conductor (EGC) between switch and recloser, and between recloser and transformer like there would be on an LV system after first disconnecting means? The multipoint grounding is throwing that off a bit for me. If required would the concentric neutral be able to double as both a neutral and EGC?
4) On the LV detla side of transformer what would the ground conductor between transformer and first disconnect means downstream be considered. To me these would be an EGC given that the neutral is derived by seperate grounding transformer. I'm used to LV application with wye secondary where SSBJ is ran between transformer and first disconnecting means downstream.
