Equipment Grounding Conductor 2002 NEC 250-122(B)

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Can someone give me some clarification regarding 250-122(B) and the sizing of equipment grounding conductor? Working on set of plans for neighborhood lighting. Connected @ 240V single phase with OCPD of 30/2 connected load varies between 8 to 12 amperes and distances from meter pedestial/panel board are 1,000 - 1400 feet - some runs with mulitiple circuits in conduits - wire has been sized for limited expansion in future - conductors are copper - 10 foot ground rods with # 4 at each pole base.
My questions are following:
1. Other than lazy enginnering why would you install three seperate grounding conductors in a single conduit run with multiple circuits?
2. I understand increasing the grounding conductor due to distance and to meet 250-122(C)I don't understand increasing grounding conductor on 1,400 foot circuit to match the phase conductor size of # 4 AWG when minimum by table 250-122 is # 10AWG. Nor do I understand using # 2 to match phase conductors in mulitple cirucuit runs (In some instance two # 2 and 1 # 4) in same conduit with mulitple circuits installed).
3. Is there a formula to use to calculate size of equipment grounding conductor required based on distance and OCPD, rather than defaulting to the size of the phase conductors?
Thanks in advance for your help and consideration.

Steve

 

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1. Other than lazy enginnering why would you install three seperate grounding conductors in a single conduit run with multiple circuits?

I see no advantage to this and of course the NEC allows running one EGC for multiple circuits.

2. I understand increasing the grounding conductor due to distance and to meet 250-122(C)I don't understand increasing grounding conductor on 1,400 foot circuit to match the phase conductor size of # 4 AWG when minimum by table 250-122 is # 10AWG.

With 15, 20 and 30 amp branch circuits the size of the EGC compared to the circuit conductors is 1 to 1.

Increase the circuit conductor from 10 AWG to 4 AWG and the EGC has to become 4 AWG to maintain the 1 to 1 ration as required by 250.122

3. Is there a formula to use to calculate size of equipment grounding conductor required based on distance and OCPD, rather than defaulting to the size of the phase conductors?

There is a formula but it is based on the phase conductors.

Equipment grounding conductors on the load side of the service disconnecting means and overcurrent devices are sized based on the size of the feeder or branch circuit overcurrent devices ahead of them. If the ungrounded conductors are increased in size to compensate for voltage drop, the equipment grounding conductors must also be increased proportionately.

Example
A 240-volt, single-phase, 250-ampere load is supplied from a 300-ampere breaker located in a panelboard 500 ft away. The conductors are 250 kcmil copper, installed in rigid nonmetallic conduit, with a 4 AWG copper equipment grounding conductor. If the conductors are increased to 350 kcmil, to what size must the equipment grounding conductor be increased?


Solution
Step 1.
Calculate the size ratio of the new conductors to the existing conductors:

Size ratio = 350,000 cir mils / 250,000 cir mils = 1.4

Step 2.
Calculate the cross-sectional area of the new equipment grounding conductor. According to Chapter 9, Table 8, 4 AWG, the size of the existing grounding conductor has a cross-sectional area of 41,740 circular mils.

Step 3.
Determine the size of the new equipment grounding conductor. Again, referring to Chapter 9, Table 8, we find that 58,436 circular mils is larger than 3 AWG. The next larger size is 66,360 circular mils, which converts to a 2 AWG copper equipment grounding conductor.

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Thank you, and have a great weekend!