Sizing EGC for Equipment wall with a ground rod

Status
Not open for further replies.
A

andykee

Member
Location
United States
I have an outdoor solar equipment wall with 12 inverters feeding breakers of a combiner panel. A ground rod is to be installed for the equipment wall. My question is relating to the size of the EGC. 250.66(A) says if I use a ground rod my EGC only has to be #6 copper even though the ungrounded conductors feeding the panel are 600mcm AL which would indicate a 1/0 copper size for the EGC(Table 250.66). Any thoughts or ideas are more than welcome!
 
andykee said:
I have an outdoor solar equipment wall with 12 inverters feeding breakers of a combiner panel. A ground rod is to be installed for the equipment wall. My question is relating to the size of the EGC. 250.66(A) says if I use a ground rod my EGC only has to be #6 copper even though the ungrounded conductors feeding the panel are 600mcm AL which would indicate a 1/0 copper size for the EGC(Table 250.66). Any thoughts or ideas are more than welcome!
Click to expand...

You are talking about the GEC, not the EGC.

The EGC is per 250.122.
The GEC is per 250.66 & 690.47.

In some cases, you can combine them and follow corresponding rules for both combined. But when the EGC has to be a lot larger than the GEC, IMO, you are asking for trouble to combine them. The EGC can simply be lug to lug, while the GEC has to be irreversibly connected (crimped, welded, etc).

It's not obvious, but 250.66 is an "OR rule", not an "AND rule". It provides the table, but allows you to ignore the table, provided you can meet any of options A through C.
 
Last edited:
If you just have one rod then you can just have a #6 per 250.66(A). The resistance of the wire is already massively lower than the resistance of the single rod's connection to earth, so it makes no functional sense for the wire to be larger.
 
jaggedben said:
If you just have one rod then you can just have a #6 per 250.66(A). The resistance of the wire is already massively lower than the resistance of the single rod's connection to earth, so it makes no functional sense for the wire to be larger.
Click to expand...

The GEC is more for voltage reference than a current path, anyway.
 
ggunn said:
The GEC is more for voltage reference than a current path, anyway.
Click to expand...

By that logic, I could use CAT5 cable as a GEC, and it would still serve the purpose of referencing voltage. I'm exaggerating, as of course that isn't NEC compliant. What exactly is the physical phenomena governs (or should govern) the sizing of the GEC?
 
Carultch said:
By that logic, I could use CAT5 cable as a GEC, and it would still serve the purpose of referencing voltage. I'm exaggerating, as of course that isn't NEC compliant. What exactly is the physical phenomena governs (or should govern) the sizing of the GEC?
Click to expand...
I said more, not exclusively. Grounding is Black Magic. :D

If you find out what the exact physical phenomenon is that should govern the size of the GEC, please let me know.
 
Status
Not open for further replies.
Top