Customer-owned equipment question.

[Tiki1469]

Please excuse any terminology mistakes I may make. I am just getting into understanding definitions.

Interesting scenario that I have read, and been told, conflicting information on. Wondering if I can get some light shed here.

Scenario: Utility 13.8kv 3phase on pole > customer-owned pole and pole-mounted cut-out fuses (this is acceptable by utility as service disconnect) > customer-owned outdoor XFMR (415/240 secondary) > (3) customer-owned interior panelboards

My current understanding is that the grounded conductor will be bonded to the grounding system at the (3) interior panelboards and the XFMR will have a 3/0 Copper cable (equipment grounding conductor???) run from each panelboard for a total of (3) 3/0 conductors.

I have read there may be a need to also bond the grounded conductor at the XFMR with a separate grounding electrode system because the XFMR is located outside of the building, but I am unsure.

 

[electrofelon]

Please excuse any terminology mistakes I may make. I am just getting into understanding definitions.

Interesting scenario that I have read, and been told, conflicting information on. Wondering if I can get some light shed here.

Scenario: Utility 13.8kv 3phase on pole > customer-owned pole and pole-mounted cut-out fuses (this is acceptable by utility as service disconnect) > customer-owned outdoor XFMR (415/240 secondary) > (3) customer-owned interior panelboards

My current understanding is that the grounded conductor will be bonded to the grounding system at the (3) interior panelboards and the XFMR will have a 3/0 Copper cable (equipment grounding conductor???) run from each panelboard for a total of (3) 3/0 conductors.

I have read there may be a need to also bond the grounded conductor at the XFMR with a separate grounding electrode system because the XFMR is located outside of the building, but I am unsure.

see 250.30(C)

 

[kwired]

see 250.30(C)

probably need to look over 225 part II as well.

 

[Tiki1469]

I'm just getting more confused reading 250.30(C). Let me ask a question that may clear this up easily for me.

In the engineered drawings for this job, the (3) Panelboards are located outdoors. Would moving the panelboards indoors change anything about the way this system is bonded or grounded?

 

[electrofelon]

Please excuse any terminology mistakes I may make. I am just getting into understanding definitions.

Interesting scenario that I have read, and been told, conflicting information on. Wondering if I can get some light shed here.

Scenario: Utility 13.8kv 3phase on pole > customer-owned pole and pole-mounted cut-out fuses (this is acceptable by utility as service disconnect) > customer-owned outdoor XFMR (415/240 secondary) > (3) customer-owned interior panelboards

My current understanding is that the grounded conductor will be bonded to the grounding system at the (3) interior panelboards and the XFMR will have a 3/0 Copper cable (equipment grounding conductor???) run from each panelboard for a total of (3) 3/0 conductors.

I have read there may be a need to also bond the grounded conductor at the XFMR with a separate grounding electrode system because the XFMR is located outside of the building, but I am unsure.

Looking at and thinking about this a little more, I have a few more comments:. Because you have a separately derived system you have a few different options. Generally you choose whether to bond at the source of the separately drive system (xformer) or the first disconnecting means. However you likely can use 250.30(A)(1) ex #2 and bond the grounded conductor at both. This is sort of an interesting exception that they kept when they got rid of the allowance to bond the grounded and equipment grounding conductors at a structure supplied by a feeder. Note that you could have separate grounded and equipment grounding conductors at the structure and run a supply side bonding jumper back to the transformer. Either way you will need a grounding electrode system at the building and at the outdoor transformer.

 

[electrofelon]

I'm just getting more confused reading 250.30(C). Let me ask a question that may clear this up easily for me.

In the engineered drawings for this job, the (3) Panelboards are located outdoors. Would moving the panelboards indoors change anything about the way this system is bonded or grounded?

By outdoors do you mean mounted on the exterior of the building or remote from the building somewhere? If you mean just on the exterior of the building then no difference.

 

[Tiki1469]

By outdoors do you mean mounted on the exterior of the building or remote from the building somewhere? If you mean just on the exterior of the building then no difference.

The drawings did not specify mounted "to" or mounted "near", just that the panels were located exteriorly to the metal building.

For sure, the drawings only called for a single grounding system and called for "3/0 "bonding jumper" from each panel back to the XFMR".

 

[electrofelon]

The drawings did not specify mounted "to" or mounted "near", just that the panels were located exteriorly to the metal building.

For sure, the drawings only called for a single grounding system and called for "3/0 "bonding jumper" from each panel back to the XFMR".

If they are remote from the building that is going to be a problem bringing multiple feeders and Branch circuits to the building per 225.30. if I recall this was relaxed a bit in the 2020, but I don't have the wording in front of me.

 

[Tiki1469]

If they are remote from the building that is going to be a problem bringing multiple feeders and Branch circuits to the building per 225.30. if I recall this was relaxed a bit in the 2020, but I don't have the wording in front of me.

250.30(A)(1) Exception No. 2: If a building or structure is supplied by a feeder from an outdoor separately derived system, a system bonding jumper at both the source and the first disconnecting means shall be permitted if doing so does not establish a parallel path for' the grounded conductor. If a grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path.

I have the 2020 if you want me to pull anything else to look at.

 

[Tiki1469]

Does this qualify us? It's (3) 1200amp Panelboards...

225.30 Number of Supplies. A building or other structure that is served by a branch circuit or feeder on the load side of a service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuitshall be considered a single circuit. Where a branch circuit or feeder originates in these additional buildings or other structures, only one feeder or branch circuit shall be permitted to supply power back to the original building or structure, unless permitted in 225.30(A) through (E).

(D) Capacity Requirements. Additional feeders or branch circuits shall be permitted where the capacity requirements are in excess of 2000 amperes at a supply voltage of 1000 volts or less.

 

[kwired]

250.30(A)(1) Exception No. 2: If a building or structure is supplied by a feeder from an outdoor separately derived system, a system bonding jumper at both the source and the first disconnecting means shall be permitted if doing so does not establish a parallel path for' the grounded conductor. If a grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path.

I have the 2020 if you want me to pull anything else to look at.

I think what that sort of was intended for though other situations might be able to take advantage of it is say you had long run of single phase and wanted to step up voltage and then step back down at the load end - this would allow you to only run two conductors if you had no other potential parallel paths besides the earth. Even a bigger advantage in that situation if you stepped it up to a medium voltage and wanted to use a coaxial type MV cable with the grounded conductor encircling the center ungrounded conductor.

 

[Tiki1469]

I think what that sort of was intended for though other situations might be able to take advantage of it is say you had long run of single phase and wanted to step up voltage and then step back down at the load end - this would allow you to only run two conductors if you had no other potential parallel paths besides the earth. Even a bigger advantage in that situation if you stepped it up to a medium voltage and wanted to use a coaxial type MV cable with the grounded conductor encircling the center ungrounded conductor.

I think I may have forgotten to add an important detail to this conversation. The XFMR is within 6-8ft of all 1200a panelboards. I could easily connect the XFMR to the grounding electrode directly. It's just the XFMR is outdoors and the panelboards are indoors. Very close to each other.

 

[Tiki1469]

The engineering calls for "ROUTE #3/0 BONDING JUMPER FROM XFMR TO EACH 1200A PANEL PER NEC REQUIREMENTS.".

The drawings do not show a separate grounding system for the XFMR, but the drawings were also calling for the panels to be put outside with the XFMR. The customer preferred to put them inside after inspection of the panel design.

This is from the 2023 NEC:
2) Outdoor Transformer.

If the transformer supplying the service is located outside the building, at least one additional grounding connection shall be made from the grounded service conductor to a grounding electrode, either at the transformer or elsewhere outside the building.

Exception:

The additional grounding electrode conductor connection shall not be made on impedance grounded systems. Impedance grounded systems shall meet the requirements of 250.36 or 250.187, as applicable.



ENHANCED CONTENT



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Outdoor installations are susceptible to lightning as well as accidental primary-to-secondary crossovers. The connection outside a building helps mitigate the effects of these influences on the interior portion of the premises wiring system. The exhibit below illustrates two grounding electrode connections — one at the service equipment installed inside the building and one installed at the transformer. At least one of those connections must be located outside the building as required by 250.24(A) (2).

 

[kwired]

I think I may have forgotten to add an important detail to this conversation. The XFMR is within 6-8ft of all 1200a panelboards. I could easily connect the XFMR to the grounding electrode directly. It's just the XFMR is outdoors and the panelboards are indoors. Very close to each other.

NEC sort of has a little bit of a grey area of consideration of anything outdoors being part of same structure if not directly attached to same structure. Only thing off top my head they specifically address is the service/feeder disconnect for mobile homes that need to be within 30 feet of the mobile home.

 

[Tiki1469]

NEC sort of has a little bit of a grey area of consideration of anything outdoors being part of same structure if not directly attached to same structure. Only thing off top my head they specifically address is the service/feeder disconnect for mobile homes that need to be within 30 feet of the mobile home.

When you say "directly attached to the same structure", are you referring to bonding to building steel, or being physically attached to the exterior building steel, or something else?

 

[kwired]

When you say "directly attached to the same structure", are you referring to bonding to building steel, or being physically attached to the exterior building steel, or something else?

Basically I mean physically mounted to the building in some way.

Something sitting on an isolated concrete pad or similar otherwise mostly fits the definition of separate structure even though it may in reality be a more direct accessory of some sort to the adjacent structure.