Parallel Conductors for Voltage Drop

[faresos]

Hello All:

I have 400A service @208V that ended up with 3-sets of 500kcmil. my question: can I run the 3-sets of 500kcmil to handhole adjacent to the main service disconnect and then transition to 1-set of 500kcmil to the main service? I just don't see that I can terminate 3-sets of 500kcmil into existing 400A disconnect.

Thanks,

 

[Smart $]

Yes, provided your calculated load does not exceed 380A, the ampacity of 500kcmil copper, 75°C terminations, assuming no adjustment and correction.

 

[Carultch]

Yes, provided your calculated load does not exceed 380A, the ampacity of 500kcmil copper, 75°C terminations, assuming no adjustment and correction.

Does the fact that these are service conductors, instead of feeder conductors, make a difference?

Not in terms of the sizing algorithm, but in terms of whether splicing / consolidating is allowed.

 

[GoldDigger]

Does the fact that these are service conductors, instead of feeder conductors, make a difference?

Not in terms of the sizing algorithm, but in terms of whether splicing / consolidating is allowed.

That should essentially be up to the POCO's rules unless the splice is on the customer side of their service point. Even then they may care if it is upstream of the meter.

 

[faresos]

Yes, provided your calculated load does not exceed 380A, the ampacity of 500kcmil copper, 75°C terminations, assuming no adjustment and correction.

Yes, the calculated load is less than 380A.

Thanks for the reply!

 

[faresos]

Does the fact that these are service conductors, instead of feeder conductors, make a difference?

Not in terms of the sizing algorithm, but in terms of whether splicing / consolidating is allowed.

The transformer (where we are running the 3-sets of kcmil from) is owned by the customer. This transformer feeds multiple buildings. Would that make a different?

 

[Smart $]

The transformer (where we are running the 3-sets of kcmil from) is owned by the customer. This transformer feeds multiple buildings. Would that make a different?

That would typically mean the run is not subject to POCO requirements. This assumes the service point and disconnecting means are on the primary side of the transformer.

 

[faresos]

That would typically mean the run is not subject to POCO requirements. This assumes the service point and disconnecting means are on the primary side of the transformer.

A follow up question. Since the transformer is not own by the utility, I assume we still do not need to run equipment ground conductor from the transformer to the disconnect, correct?

 

[Smart $]

A follow up question. Since the transformer is not own by the utility, I assume we still do not need to run equipment ground conductor from the transformer to the disconnect, correct?

Paraphrased, a supply-side bonding jumper (SSBJ) is required but excepted to permit bonding by way of the grounded conductor with a system bonding jumper at both an outdoor transformer and its secondary disconnecting means, and no other metallic pathways between source and disconnect. See 250.30(A)(1) Exception No. 2 for actual wording.

 

[Carultch]

The transformer (where we are running the 3-sets of kcmil from) is owned by the customer. This transformer feeds multiple buildings. Would that make a different?

Yes. 240.21(C) rules would apply. The conductors from a customer-owned transformer would classify as transformer secondary conductors, instead of service conductors (as is the case for a utility-owned transformer). There are none of those rules that prohibit splicing/consolidating, however most of those rules require as much amps of wire at every cross section as you have of OCPD. So single 500 kcmil would be insufficient, and you'd need to step to either 2 sets of min 3/0 or 1 set of 600.

 

[Smart $]

.... So single 500 kcmil would be insufficient, and you'd need to step to either 2 sets of min 3/0 or 1 set of 600.

Good catch! :happyyes: