208/120V 4-Wire Feeders. How do I decide if neutral is current carrying?

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Jon456

Jon456

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Location
Colorado
In a commercial building, there is an existing 208V 3-phase 100A fused disconnect feeding a 225A panelboard. The existing feeders are 1 AWG THW aluminum conductors (current carrying & grounded). The space being served by this panelboard is being renovated and the new calculated load will be ~80A. There will be a mix of 208 & 120V resistive loads, some 120V fan motors, and one piece of equipment with a 3-phase 208V/10A VFD driving a motor. All the troffer lighting will be replaced with LED fixtures except for one small room which may retain its single existing 4-bulb T-8 fixture.

My question is, at what non-linear load threshold is the neutral considered a current carrying conductor? I'm hoping it can be considered non-current-carrying so I don't have to derate the feeders and replace the existing ones.
 
infinity

infinity

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New Jersey
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The threshold is more than 50% non-linear to count the neutral a s CCC. From what you've described you do not need to worry about it.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Jon456 said:
In a commercial building, there is an existing 208V 3-phase 100A fused disconnect feeding a 225A panelboard. The existing feeders are 1 AWG THW aluminum conductors (current carrying & grounded). The space being served by this panelboard is being renovated and the new calculated load will be ~80A. There will be a mix of 208 & 120V resistive loads, some 120V fan motors, and one piece of equipment with a 3-phase 208V/10A VFD driving a motor. All the troffer lighting will be replaced with LED fixtures except for one small room which may retain its single existing 4-bulb T-8 fixture.

My question is, at what non-linear load threshold is the neutral considered a current carrying conductor? I'm hoping it can be considered non-current-carrying so I don't have to derate the feeders and replace the existing ones.
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The qualification is if a "majority of the load" is non linear. Unfortunately, the code seems to be black and white on it: there doesnt seem to be any allowance for "how non linear" those loads are. I would not count the neutral as a CCC from what you describe and I bet 99% of others on this forum would do the same.
 
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