Grounded Conductor Sizing for Parallel Feeder

[JC_ELEC]

Hello, i'm a bit confused about grounded conductor sizing for parallel feeders. Nec 215.2(B) states the following:

"The size of the feeder circuit grounded conductor shall not be smaller than the equipment grounding conductor size required by 250.122, except that 250.122(F) shall not apply where grounded conductors are run in parallel"

So it says that 250.122(F) shall not apply for parallel runs. So, does that mean that 250.122 won't dictate the minimum neutral conductor size for a parallel run? Here is an example:

In this scenario i have a 1000A 3phase Breaker in a Switchboard feeding a 1000A Panelboard. The neutral load is non-existent but the client wants a minimum sized neutral conductor (don't ask why, it's an example). The conductors sizing are as follows:
- Ungrounded conductors sizing: 5 x #3/0AWG (200A) per phase = 1000A.
- 5 x EMTs (one per parallel set).
- Equipment Grounding Conductor: 5 x #2/0AWG EGC (per table 250.122).
- Grounded/Neutral Conductor: can i size the minimum neutral conductor as 5 x #1/0AWG (minimum size for parallel neutral size per 310.10(G)(1)? Or do i have to size the neutral in each set per the minimum allowed size in 250.122 (in this case 5 x #2/0AWG)?

 

[infinity]

Would this apply? Sounds like #1/0 would be compliant becasue they're in parallel.

215.2(A)(1)(a)
Exception No. 3: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the continuous and noncontinuous load. (b)The minimum feeder conductor size shall have an ampacity not less than the maximum load to be served after the application of any adjustment or correction factors in accordance with 310.14.)

 

[LarryFine]

A neutral must be at least large as the EGC, and for the same reason: to reliably operate OCP.

 

[infinity]

A neutral must be at least large as the EGC, and for the same reason: to reliably operate OCP.

Even for 5 sets in parallel?

 

[JC_ELEC]

A neutral must be at least large as the EGC, and for the same reason: to reliably operate OCP.

So in your opinion, what does “except that 250.122(F) shall not apply where grounded conductors are run in parallel” in 215.2(B) implies? What do you think the code is trying to explain there?

 

[LarryFine]

I'm not really sure.

 

[wwhitney]

So in your opinion, what does “except that 250.122(F) shall not apply where grounded conductors are run in parallel” in 215.2(B) implies?

For example, 250.122(F)(1)(b) says that each EGC in a set of parallel conduits must be full-sized. That won't apply to the parallel grounded conductors. So in your example in the OP, the EGC in each conduit has to be 2/0, but the neutral in each conduit can be 1/0.

Cheers, Wayne

 

[infinity]

For example, 250.122(F)(1)(b) says that each EGC in a set of parallel conduits must be full-sized. That won't apply to the parallel grounded conductors. So in your example in the OP, the EGC in each conduit has to be 2/0, but the neutral in each conduit can be 1/0.

Cheers, Wayne

I agree. The grounded conductor is sized according to the load. Since this has 5 sets of conductors even with a small neutral load the minimum size grounded conductor in each set is #1/0 due to the minimum parallel rule. And since there is more than one set the combined grounded conductor size of the 5 sets is actually larger than the minimum EGC size of #2/0.