Long distance ground size

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Doctor Electric

Doctor Electric

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Hey guys I got a situation where a customer is building a house approximately 270 ft from the roadway we are up sizing the service wire it is only a two hundred amp service. Because of the length of the run am I required to upsize my ground as well as the feeders. Ground sized off of ocp for 200 amp is #4 cu so 350 kcmil in a pipe with #4 ground??? Any thoughts would be helpful. Thanks guys
 
Isn't there a type of utility disconnect that allows the run to still be service conductors, and the house disconnect to be the main?
 
Equipment ground for a 200A feeder is #6 copper, not 4. So you can start your upsizing from that size. EDIT - you probably meant #4 AL which is correct for aluminum.

Also not sure if you are required to upsize the feeder at all. What is the load calc? Is the space and water heat all electric (which won't care about voltage drop)? Are there large motors? The power company would maybe only run a 4/0 or 250 that far because they know the average load on a house is much smaller than what NEC load calculations require. My "200A" house service is 175' from the transformer and it has half #2 AL overhead and half 1/0 AL underground. I have all gas appliances though, its only the air conditioner that causes a nice flicker.
 
suemarkp said:
Equipment ground for a 200A feeder is #6 copper, not 4. So you can start your upsizing from that size. EDIT - you probably meant #4 AL which is correct for aluminum.

Also not sure if you are required to upsize the feeder at all. What is the load calc? Is the space and water heat all electric (which won't care about voltage drop)? Are there large motors? The power company would maybe only run a 4/0 or 250 that far because they know the average load on a house is much smaller than what NEC load calculations require. My "200A" house service is 175' from the transformer and it has half #2 AL overhead and half 1/0 AL underground. I have all gas appliances though, its only the air conditioner that causes a nice flicker.
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The ground for the ocpd would be #4. Equipment bonding jumpers would be number 6
roger said:
250.122 (B)


Roger
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Thank you Rodger
 
250. 122 B increased in size. Where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation wire type equipment grounding conductors where installed shall be increased in size proportionately according to the circular mil area of the ungrounded conductors
 
Doctor Electric said:
250. 122 B increased in size. Where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation wire type equipment grounding conductors where installed shall be increased in size proportionately according to the circular mil area of the ungrounded conductors
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So it would be a number two cu ground or one ot aL
 
Doctor Electric said:
So it would be a number two cu ground or one ot aL
Click to expand...

Determine the minimum size for ampacity, if length were negligible. I call this the "minimum local size".
Determine the corresponding EGC size from Table 250.122. The default ground size.

Compare the kcmil of what you are actually using, to the kcmil of the minimum local size. Compare it as an upsize ratio.
Multiply the upsize ratio by the kcmil of the previously determined default EGC size. That becomes your EGC required for upsizing.

Generally, if you upsize the main wires X increments of sizes, you'll correspondingly upsize the EGC the same number of gauge size increments. This is because the gauge numbering is defined as a logarithmic scale of kcmil, where incremental steps in nominal gauge size represent multiplicative changes in kcmil.

It is OK to splice this locally at the terminal equipment, in order to adapt to a size that fits in factory lugs. Obviously, it needs to be at least the size determined from Table 250.122. The physical basis for the EGC upsizing rule, is to make sure the EGC resistance isn't too high to prevent it from being an effective ground fault current path. The sizing in table 250.122 is to size it large enough to keep it from melting like a fuse during fault current conditions. Upsizing after that, is to reduce its total ohms when length is significant.
 
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