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)

 

[infinity]

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.

Correct, which is why the conductor circled in red is not required to be larger than #4 because it is connecting the CEE to the other electrode.

 

[zemingduan]

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.

250.66 is for the size of grounding electrode conductors. Below is the definition of grounding electrode conductors from the code book (NEC 2017).

Grounding Electrode Conductor. A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system. (CMP-5)

What confused me the most is that the in NEC 2017 the 250.66 calls the conductor that connect the two electrodes the "bonding jumper" in the 250.66. So this "bonding jumper" that connects two electrodes is also a GEC? I am not sure if I read the definition of GEC correctly.

 

[infinity]

What confused me the most is that the in NEC 2017 the 250.66 calls the conductor that connect the two electrodes the "bonding jumper" in the 250.66. So this "bonding jumper" that connects two electrodes is also a GEC? I am not sure if I read the definition of GEC correctly.

The jumper between two electrodes is a bonding jumper. It is not a GEC because as per the definition it would need to connect the electrode directly to the system neutral or grounded conductor.

 

[zemingduan]

The jumper between two electrodes is a bonding jumper. It is not a GEC because as per the definition it would need to connect the electrode directly to the system neutral or grounded conductor.

If it is not a GEC, why it shall be sized based on the 250.66? If you read 250.66, it only says the GEC connect to CEE is not required to be larger than #4. I think 250.66 doesn't say that the bonding jumper connected to the CEE is not required to be larger than #4.



Thanks...

 

[infinity]

If it is not a GEC, why it shall be sized based on the 250.66? If you read 250.66, it only says the GEC connect to CEE is not required to be larger than #4. I think 250.66 doesn't say that the bonding jumper connected to the CEE is not required to be larger than #4.

View attachment 2580486

Thanks...

Good question. I'll have to think about. Also Table 250.102(C)(1) has a list of conductors that the table applies to. A bonding jumper between two electrodes is not one of them.

 

[zemingduan]

I am looking forward to you guys opinions. One thought, if you read the definition of GEC in the below manner, the bonding jumper that connects the two electrodes is a GEC.

Grounding Electrode Conductor. A conductor used to connect the system grounded conductor or the equipment (an electrode like the building steel is the equipment here) to a grounding electrode (like the CEE) or to a point on the grounding electrode system. (CMP-5)

The NEC defines the equipment as below. An electrode is an equipment?

Equipment. A general term, including fittings, devices, appliances, luminaires, apparatus, machinery, and the like used as a part of, or in connection with, an electrical installation. (CMP-1)

 

[infinity]

I am looking forward to you guys opinions. One thought, if you read the definition of GEC in the below manner, the bonding jumper that connects the two electrodes is a GEC.

Grounding Electrode Conductor.
A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system.

The equipment mentioned in the definition would be for something like a panel in a separate structure where the GEC is run from the electrode to the equipment grounding terminal or bus and is not connected to the neutral.

 

[zemingduan]

The equipment mentioned in the definition would be for something like a panel in a separate structure where the GEC is run from the electrode to the equipment grounding terminal or bus and is not connected to the neutral.

Yeah. I know what you mean. I hope some one can shade more lights on this. This being confusing me for a long time..

 

[infinity]

Yeah. I know what you mean. I hope some one can shade more lights on this. This being confusing me for a long time..

The way I visualize it is that the GEC connects an electrode to the service neutral. Everything else that doesn't directly connect the service neutral is a bonding jumper. A sub-panel in a separate structure would be an exception because the GEC would connect to the equipment grounding conductor.