Oversized Feeders and Associated Equipment Grounding Conductors

[thepatriotengineer]

NEC 250.122(B): New for 2020 - If ungrounded conductors are increased in size.....wire-type equipment grounding conductors (EGC) shall be increased in size proportionally to the increase in circular mil area of the ungrounded conductors.

See calculation example in NEC Handbook.

Another example: 200A feeder, 250kcmil AL wire upsized to 900kcmil AL to compensate for voltage drop - normally the EGC would be #6CU, per NEC 250.122(A).
900000 / 250000 = 3.6; from Table 8 in Chapter 9, area of #6CU = 26240cmil, so the area of the upsized EGC = 3.6 * 26240 = 94464.
Upsized EGC = #1/0CU

Question: Suppose the distance is long enough to require a parallel 900AL feeder (2 sets), is this calculation based off the total area (1800kcmil) or the area of just one of the feeders (900kcmil)? It's a difference of #1/0CU EGC vs. #4/0CU EGC in each feeder.....and at the distances involved, that becomes very expensive quickly.

 

[LarryFine]

Welcome to the forum.

All the more reason to get the transformer as close to the load as possible.

 

[jaggedben]

...

Question: Suppose the distance is long enough to require a parallel 900AL feeder (2 sets), is this calculation based off the total area (1800kcmil) or the area of just one of the feeders (900kcmil)? It's a difference of #1/0CU EGC vs. #4/0CU EGC in each feeder.....and at the distances involved, that becomes very expensive quickly.

Based off the total area.

This is not new in the 2020 NEC. I think it just got renumbered.

 

[infinity]

Question: Suppose the distance is long enough to require a parallel 900AL feeder (2 sets), is this calculation based off the total area (1800kcmil) or the area of just one of the feeders (900kcmil)?

Since you have 2 sets of 900's you would use the combined size of 1800 kcmils to calculate the EGC size.

 

[tom baker]

Parallel 900’s? Did you consider a step up to MV and back to secondary voltage?

 

[thepatriotengineer]

Parallel 900’s? Did you consider a step up to MV and back to secondary voltage?

not for a single feeder inside a warehouse. much more expensive.

 

[thepatriotengineer]

Based off the total area.

This is not new in the 2020 NEC. I think it just got renumbered.

thank you

 

[infinity]

not for a single feeder inside a warehouse. much more expensive.

Are you really planning on using 900 kcmil conductors or is this a theoretical question?

 

[electrofelon]

Are you really planning on using 900 kcmil conductors or is this a theoretical question?

No offense to the OP, but I hear something like that and, unless it's a theoretical question, I question whether they know what they are doing. Perhaps the OP could supply more details such as voltage and length and we can offer some suggestions.

 

[infinity]

No offense to the OP, but I hear something like that and, unless it's a theoretical question, I question whether they know what they are doing. Perhaps the OP could supply more details such as voltage and length and we can offer some suggestions.

I know that some designers just look at the chart and pick a conductor size or they use a voltage drop calculator and it spits out 900 kcmil. For us we never install anything larger than 750's.