EGC Size

A

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
IS it necessary to upsize the EGC size for multiple sets as the schedule below calls for. I also suspect that in some cases the upsizing in the EGC may require larger conduit. I thought the EGC was based on OCPD size. I have 7 sets of feeder 380B. So I guess I would need #250 or 500 EGC thus I don;t think 3-1/2" conduit would work for 4 #500.

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Alwayslearningelec said:
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At 2000 amps, 7 sets of 500 is a lot of extra ampacity. I would guess they must be increasing the feeder because of voltage drop. When you increase the feeder for voltage drop you must increase the size of the EGC proportionally. My first thought with the partial picture is that the "feeder" you are showing is actually service entrance conductors which wouldn't have a neutral.
 
Strathead said:
At 2000 amps, 7 sets of 500 is a lot of extra ampacity. I would guess they must be increasing the feeder because of voltage drop. When you increase the feeder for voltage drop you must increase the size of the EGC proportionally. My first thought with the partial picture is that the "feeder" you are showing is actually service entrance conductors which wouldn't have a neutral.
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It's feeding cable top box.

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infinity said:
There is no corresponding EGC for 7 sets on your chart. The 7 sets is oversized for 2000 amps so is the EGC. So what's the question?
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I was wondering if it is necessary to upsize EGC for multiple sets but you answered and it makes sense that more size larger OCPD thus larger EGC.
 
Strathead said:
Again, what feeds the tap box, I am thinking this is a service, or a separately derived system fed from an exterior medium voltage transformer. As such it isn't even going to have a ground regardless of what this says.
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In post #5 it appears to be a feeder.
 
Alwayslearningelec said:
IS it necessary to upsize the EGC size for multiple sets as the schedule below calls for. I also suspect that in some cases the upsizing in the EGC may require larger conduit. I thought the EGC was based on OCPD size. I have 7 sets of feeder 380B. So I guess I would need #250 or 500 EGC thus I don;t think 3-1/2" conduit would work for 4 #500.

View attachment 2580360
Click to expand...
First of all there is no x7 column for the EGC on the chart.:rolleyes:

Second based on 7 sets one could assume AL conductors. 7 x 310 ( 500 al@75c)=2170. May have missed copper conductor some where.

Based on that I would go to 250.122 and see what size requires for the 2000 amp OCPD. This would require a 250 cu or 400 AL. That would be 3- 500 AL and 1- 400 AL in each raceway. Assuming thhn/ thwn conductors this would easily fits in a 3.5" raceway. The feeder, P380B shows 3-500 + EGC.

Table 4, 3.5" emt@100%=11.545 in²
Table 5,
500 thhn, .7073 in² x 3= 2.1219 in²
400 thhn ( EGC) .5863

2.1219+.5863= 2.7082 in²
2.7082/11.545= .23457 or 23.457% fill
Way under the over 2 wires 40% fill allowence.

At 4-500s it's still way under 40% fill.
4 x .7073= 2.8292/11.545= .25049 or 25%

Also annex C shows 6-500s in a 3.5" emt,
guessed emt. Worse case sch 80 pvc it shows 5- 500s

If the wire was CU than the engineer or the NEC could require a larger than 250 cu EGC in each raceway depending on year of code.

If an increase is required, using CU it would take a 400 CU EGC.
7 x 500= 3500 mcm ( shown on plans)
7 x 350 = 2450 mcm (minimum required)
250x(3500/2450)= 357.14 mcm

2000/7= 285.71, 350 mcm @75 c = 310 amps.
310 x 7= 2,170 amps.
285 x 7= 1,995 amps

Can not use 300 @285 you must round up to the next size.

So I would ask the engineer AL or CU and what size of EGC for the seven sets.
 
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