sizing grounds for parallel conductors

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doug elias

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In an installation where parallel 3/0 conductors
have been installed to compensate for voltage drop, what code article dictates the size of the
grounding conductor? Are these conductors considered " Increased in size" per 250-122(B)
or are they considered "Conductors in Parallel"
per 250-122(F) The installation is for a 120/208 volt 225 amp 3 phase/4 wire panel located approx. 550' from the 200 amp disconnect that feeds it. this panel is fed by (2) sets of (4)
3/0 conductors in 3" pvc conduit
 
Re: sizing grounds for parallel conductors

You would have to use both.

You would start with table 250.122 and get the size required based on the rating of the device. You would then determine the increase of size of the ungrounded conductors as a percentage. You would then increase the 250.122 value by the percentage of increase.

Make sense?
 
Re: sizing grounds for parallel conductors

Ryan: yes and no. 250-122(B) directs us to increase the size of the gounding conductor relative to the increase in size of the feeder conductor,but 250-122(F) takes into account that the circular mils for the grounding has basically
doubled because you have a full size grounding conductor (rated on the overcurrent protection)
in each of the raceways. Based on 250-122(B):
2 sets of (4) 3/0 in 3" pvc raceways fed from a
200 amp disconnect would require a #3 ground
 
Re: sizing grounds for parallel conductors

Perfect! You increased from 3/0 to (2) 3/0 to accomodate voltage drop, which is an increase of 100%. You then take your 6 AWG EGC conductor and increase it by 100% of it's circular mil, which would result in 3 AWG required.
 
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