Electrodes Bonding Jumper VS Grounding Electrodes Conductor

[zemingduan]

1. The conductor circled in above screenshot is bonding jumper instead of grounding electrode conductor according to the NEC definition. Do you size this conductor according to 250.66 or 250.102? I see many people size it according to 250.66 (B) and use #4 Cu. But I think per code it should be sized according to 250.102. And 250.102 requires it to be larger than 3/0 Cu depending on the incoming service conductors size.

2. When you bond the building steel to the concrete encased electrodes, the bonding jumper from building steel to the concrete encased electrodes shall follow the 250.102 and may be required larger than #3/0 Cu depending on the service conductor size. However the GEC from neutral to the building steel (not shown in the screen shot above but if we have one) follows 250.66 and is not required to be larger than #3/0 Cu. Why?

Besides when you connect the neutral conductor directly to the concrete encased electrodes, the GEC is not required to be larger than #4 Cu according to 250.66 (B).

I know they are code requirements, but i can not understand the logic/insight behind it. It doesn't make sense to me. Can someone explains it to me?

Thanks!

 

[infinity]

The building steel is bonded via the bonding jumper to the water pipe. The bonding jumper in the red circle is the connection to the CEE which is not required to be larger than #4.

 

[don_resqcapt19]

It is sized based on 250.66 and the electrode that it is connected to, or where the the jumper is connected to multiple electrodes, the largest size required for any of the electrodes that are connected by that bonding jumper.

One of the biggest reason table 250.102(C)(1) was added was to clear up the confusion as two when a conductor larger than 3/0 is required. Grounding electrode conductors and grounding electrode bonding jumpers are never required to be larger than 3/0.

To add additional clarity a new definition for grounding electrode bonding jumper was added in the 2026 code.

Bonding Conductor, Grounding Electrode (Grounding Electrode Bonding Jumper). (Grounding Electrode Bonding Conductor)
A conductor, other than the grounding electrode conductor, used to interconnect two or more grounding electrodes to form the grounding electrode system. (CMP-5)