Patrick Anderson
Member
- Location
- Portland, Oregon. USA
I am currently preparing to install a 4000 amp feeder to a induction furnace. It will be (5 wire system) 3 phases, ground and neutral conductor all paralleled originating from a new substation (treated like service / separately derived system). Our secondary breaker is actually a 4000 amp frame with 3000 amp rating plug installed. We will install 8 - 500 mcm's for a combined amperage of 3,040 amps.
Attempting to size the proper grounded conductor. My local JHA contends that we use 250.66 and calculate it as over 1100 kcmils copper. Which is fine I agree and generally assume 3/0 if it was in a single raceway.
My conflict / argument of this 3/0 arises from from the note 1 of table 250.66. I see this as multiple sets of conductors / paralleled. And this note states that the equivalent size shall be determined by the largest sum of the corresponding conductors of each set. (Each set being the key word) Would that not mean each paralleled set of 500 mcm would be used for the calculation. Thereby resulting in the grounded conductor being sized @ 1/0.
The bottom of that same note also states that this table also applies to separately derived conductors.Which is what we have.
Your feed back would be greatly appreciated
Attempting to size the proper grounded conductor. My local JHA contends that we use 250.66 and calculate it as over 1100 kcmils copper. Which is fine I agree and generally assume 3/0 if it was in a single raceway.
My conflict / argument of this 3/0 arises from from the note 1 of table 250.66. I see this as multiple sets of conductors / paralleled. And this note states that the equivalent size shall be determined by the largest sum of the corresponding conductors of each set. (Each set being the key word) Would that not mean each paralleled set of 500 mcm would be used for the calculation. Thereby resulting in the grounded conductor being sized @ 1/0.
The bottom of that same note also states that this table also applies to separately derived conductors.Which is what we have.
Your feed back would be greatly appreciated