Grounding in relation to voltage drop wire sizing

[RodneyMcDonald]

Thank you guys for your help on this one... I’ve looked this up and get mixed results so here goes...
I have a 3000’ underground run on a 30amp single pole breaker 277v... I will not bore you with my volt calc but I will be cascading from #2 cu down to #8 cu...
30 amp breaker requires a #10thhn
Can I use #10 thhn from beginning to end of this circuit or must I size the grounding conductor to the current carrying conductor as appropriate as i cascade down to my desired #8?
im sure someone has referenced this in code book before but I’m simply unable to find specific article identifying an answer to my question.. thank you for your patience and help in this...

 

[don_resqcapt19]

Where the overcurrent protective device is 30 amps or less and you increase the size of the ungrounded conductors, the EGC must match the size of the ungrounded conductors. 250.122(B)

 

[Carultch]

Thank you guys for your help on this one... I’ve looked this up and get mixed results so here goes...
I have a 3000’ underground run on a 30amp single pole breaker 277v... I will not bore you with my volt calc but I will be cascading from #2 cu down to #8 cu...
30 amp breaker requires a #10thhn
Can I use #10 thhn from beginning to end of this circuit or must I size the grounding conductor to the current carrying conductor as appropriate as i cascade down to my desired #8?
im sure someone has referenced this in code book before but I’m simply unable to find specific article identifying an answer to my question.. thank you for your patience and help in this...

Please explain what you mean by "cascade". I have a guess, but I may have a different understanding than what you meant.

If you are talking about needing to step your #2 egc down to a #8 or #10, in order to fit in the terminals of your source and load, that is what you'd have to do. It would meet the intent of the NEC's requirement to upsize EGC, as long as the smaller segment is kept short. Short in the sense that you probably do this splice in enclosure of where you terminate the circuit, or immediately adjacent thereto. Once the circuit starts running a significant distance, you'd have to have it equal the ungrounded conductor for this circuit.

The intent of this requirement is to keep the total resistance of the EGC within reasonable limits, so it can effectively trip the breaker in the event of a fault. A single foot of #8 or #10 at each end, will be a tiny fraction of the total resistance of 3000 ft of #2.

 

[RodneyMcDonald]

Please explain what you mean by "cascade". I have a guess, but I may have a different understanding than what you meant.

If you are talking about needing to step your #2 egc down to a #8 or #10, in order to fit in the terminals of your source and load, that is what you'd have to do. It would meet the intent of the NEC's requirement to upsize EGC, as long as the smaller segment is kept short. Short in the sense that you probably do this splice in enclosure of where you terminate the circuit, or immediately adjacent thereto. Once the circuit starts running a significant distance, you'd have to have it equal the ungrounded conductor for this circuit.

The intent of this requirement is to keep the total resistance of the EGC within reasonable limits, so it can effectively trip the breaker in the event of a fault. A single foot of #8 or #10 at each end, will be a tiny fraction of the total resistance of 3000 ft of #2.

I will be dropping load totals at each pole so 10 amps at 1st pole 9 amps 2nd so on and so forth till last pole at .93 amps...
#2 steps down to #4 to #6 ect... that’s all I was referring to but I’m getting the sense that the EGC needs to be sized to the current carrying conductor as it ‘cascades’ down in size... thank you for your help

 

[kwired]

Where conductor size is increases because of voltage drop EGC must also be increased proportionally in size.

Since your 30 amp circuit would normally require a 10 AWG copper EGC and your circuit conductors would also have a minimum size of 10 AWG copper, proportional increases of the EGC results in same size conductor as the circuit conductor every time.

If you would have had say a 50 amp circuit that normally would require 10 AWG EGC but a 8 or 6 (temp rating can come in here) for the circuit conductors then it would still be pretty likely an increase in circuit conductor size for VD with proportional increase in EGC still leaves you with a smaller conductor for EGC than you have for circuit conductors.