Avoid Parallel Ground Paths when Grounding a Multiple Points

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Leo1

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The NEC require a service be grounder at the source or first disconnect. In addition, if the sourced is an outside transformer it shall also be grounded. NEC - 250.30 (A)(1) excep. 2 allows multiple ground points provided a parallel path for the ground conductor is not established. How is this best achieved?
 
Leo1 said:
The NEC require a service be grounder at the source or first disconnect. In addition, if the sourced is an outside transformer it shall also be grounded. NEC - 250.30 (A)(1) excep. 2 allows multiple ground points provided a parallel path for the ground conductor is not established. How is this best achieved?
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By only bonding the SDS once.
 
Leo1 said:
The NEC require a service be grounder at the source or first disconnect. In addition, if the sourced is an outside transformer it shall also be grounded. NEC - 250.30 (A)(1) excep. 2 allows multiple ground points provided a parallel path for the ground conductor is not established. How is this best achieved?
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This outside transformer is Utility owned. But if the transformer were provided by the facility owner, how does the NEC requirement changes with respect to avoiding parallel ground paths?
 
Leo1 said:
This outside transformer is Utility owned. But if the transformer were provided by the facility owner, how does the NEC requirement changes with respect to avoiding parallel ground paths?
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because the electrons know who owns what so there is no possibility of objectionable current flow.
 
Leo1 said:
This outside transformer is Utility owned. But if the transformer were provided by the facility owner, how does the NEC requirement changes with respect to avoiding parallel ground paths?
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The requirements change only because the NEC does not apply to the utilities.

For privately owned systems wouldn't you agree that only bonding the grounded conductor once is the best method to avoid parallel paths?
 
Leo1 said:
This outside transformer is Utility owned. But if the transformer were provided by the facility owner, how does the NEC requirement changes with respect to avoiding parallel ground paths?
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There is no NEC requirement to have a single point earthing system, if that is what you are asking and concerned about
 
if the utility owns the transformer, and say its 120/240 3 wire service, the neutral is a white wire with an imaginary green stripe.

If its a customer owned transformer then the NEC allows the SBJ at the source or first disconnect, but not both. There are two ways to wire the transformer secondary, one is with a green and white wire, the other with a white wire and the imaginary green stripe, how its done is determined by the location of the SBJ.
In each case there will be no parallel path.
 
electrofelon said:
I'm not sure if the op is asking about a service or a sds. He seems to be lumping together both with his wording and references....
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Used to believe otherwise, but now I don't believe there is such a thing as a consumer-owned service transformer. Code permits certain items to be connected to service conductors before the service disconnecting means. A transformer is not one of them.

On the utility side of the service disconnecting means (of a grounded system), the grounded conductor is use to bond all conductive enclosures and raceways. 250.30(A)(1) Exception No. 2 does not apply.

250.30(A)(1) Exception No. 2 permits an outside SDS transformer supplying a building or structure to be connected in a manner quite similar to a service transformer. To do so, there can be no SSBJ as permitted by 250.30(A)(2) Exception. This latter exception was finally realized and put in the 2014 Code... but in prior editions, it is impossible to bond at both the transformer and its disconnecting means without creating a parallel path for grounded conductor current.
 
IMHO there can be a customer owned service transformer as long as it is POCO operated and is located on the POCO side of the service point.
I agree that if there is no disconnect with OCPD on the primary side then the service point cannot be in the primary side either. :)
 
GoldDigger said:
IMHO there can be a customer owned service transformer as long as it is POCO operated and is located on the POCO side of the service point.
I agree that if there is no disconnect with OCPD on the primary side then the service point cannot be in the primary side either. :)
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Then stating it another way: There can be no service transformer under the purview of the NEC.
:D
 
iwire said:
Tom, under an exception the NEC allows it at both. I believe that is what the OP is asking about
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Correct. The NEC exception allows both and the NEC states if the transformer is outside then an additional ground shall be made. My original question assumed a new service versus an SDS.

For a service the only way I know to be Code compliant of grounding at the first main disconnect and at an outside transformer, whether owner supplied or utility owned, is to ground the outside transformer to earth, then route the neutral and ungrounded conductors from the transformer to the first main disconnect in a non-metallic raceway (PVC for example) and no equipment ground. Then the ground to earth could also be made at the first main disconnect without a parallel ground path between the grounded transformer and first main disconnect.
 
Smart $ said:
Used to believe otherwise, but now I don't believe there is such a thing as a consumer-owned service transformer. Code permits certain items to be connected to service conductors before the service disconnecting means. A transformer is not one of them.

On the utility side of the service disconnecting means (of a grounded system), the grounded conductor is use to bond all conductive enclosures and raceways. 250.30(A)(1) Exception No. 2 does not apply.

250.30(A)(1) Exception No. 2 permits an outside SDS transformer supplying a building or structure to be connected in a manner quite similar to a service transformer. To do so, there can be no SSBJ as permitted by 250.30(A)(2) Exception. This latter exception was finally realized and put in the 2014 Code... but in prior editions, it is impossible to bond at both the transformer and its disconnecting means without creating a parallel path for grounded conductor current.
Click to expand...

Not sure I am correct but I think there is a way to ground at both locations and not create a parallel path: ground the outside transformer to earth as required by Code, then route the neutral and ungrounded conductors from the transformer to the first main disconnect in a non-metallic raceway (PVC for example) and no equipment grounding conductor. Then the ground to earth could also be made at the first main disconnect without a parallel ground path between the grounded transformer and first main disconnect. Correct?
 
Leo1 said:
Not sure I am correct but I think there is a way to ground at both locations and not create a parallel path: ground the outside transformer to earth as required by Code, then route the neutral and ungrounded conductors from the transformer to the first main disconnect in a non-metallic raceway (PVC for example) and no equipment grounding conductor. Then the ground to earth could also be made at the first main disconnect without a parallel ground path between the grounded transformer and first main disconnect. Correct?
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You would be implementing 250.30(A)(1) Exception No. 2 and 250.30(A)(2) Exception in concert (i.e. both)... so yes.

Note that "ground the outside transformer to earth" is not explicitly required for an outside SDS.
 
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