EGC Same Size as Phase Conductors

[jtinge]

For years my company has required EGC's to be the same size as phase conductors for branch circuits up to 100A. This exceeds the NEC requirements based on Table 250.122. When asked for the basis of this requirement, no one can show me the rationale for this practice. I have heard this may be a conservative common practice for some engineering firms but it seems to unnecessarily oversize the EGC but I have heard no good explanation for this practice. Can anyone shed light on this practice? Is it common, or an outdated legacy practice? What size branch circuits did it apply if other than the 100A threshold at my company?

 

[ron]

I require the grounded conductor to match the phase (ungrounded), but for EGC I follow 250.122.
Not heard of matching ungrounded to EGC before, except upsizing as needed for voltage drop.

 

[bob]

There is no rationale. If fact there is no basis for table 250.122. The information in this table has no engineering basis. There have been efforts to change it but so far nothing has happened.

 

[jtinge]

I hear the arguement that EGC sizes based on Table 250.122 are adequate based on experience. I have seen one recommendation to base EGC sizes based on the thermal damage curve of the EGC once the protective device coordination is done. Some might say this is overkill. But without any other technical insight, I don't feel I can justify sizing EGC's the same size as phase conductors if the NEC requirements allow a smaller EGC.

 

[steve66]

For years my company has required EGC's to be the same size as phase conductors for branch circuits up to 100A. This exceeds the NEC requirements based on Table 250.122. When asked for the basis of this requirement, no one can show me the rationale for this practice. I have heard this may be a conservative common practice for some engineering firms but it seems to unnecessarily oversize the EGC but I have heard no good explanation for this practice. Can anyone shed light on this practice? Is it common, or an outdated legacy practice? What size branch circuits did it apply if other than the 100A threshold at my company?

Never heard of that. Are you sure they weren't refering to the neutral conductor being the same size as the phase conductors?