Difference between System Bonding Jumper and Main Bonding Jumper

[Dennis Alwon]

Can someone explain the difference between these two animals. The system jumper seems to add "at a separately derived system" but aren't all services a separately derived system.

Bonding Jumper, Main. (Main Bonding Jumper)
The connection between the grounded circuit conductor and the equipment grounding conductor, or the supply-side bonding jumper, or both, at the service. (CMP-5)

Bonding Jumper, System. (System Bonding Jumper)
The connection between the grounded circuit conductor and the supply-side bonding jumper, or the equipment grounding conductor, or both, at a separately derived system. (CMP-5)

 

[infinity]

I would not consider a service to be an SDS.

 

[wwhitney]

Can someone explain the difference between these two animals.

The only difference is the MBJ is at a service, and an SBJ is not. The difference is terminological, not electrical.

The system jumper seems to add "at a separately derived system" but aren't all services a separately derived system.

No, per the definition:

Separately Derived System. An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.

Cheers, Wayne

 

[LarryFine]

It sounds to me like the basic difference is the SBJ is a the point of the system origin (transformer secondary), and the MBJ is at the point of use (premises service). Kinda theirs vs ours.

The former establishes the source as a grounded system, and the latter establishes the EGC pathway.

 

[Dennis Alwon]

Thanks, I was confused because I considered a service a separately derived system. It clearly is not.

 

[jaggedben]

Another difference is that a service may be actually bonded (and grounded) elsewhere than at the MBJ. (e.g. meter socket) An SDS is not supposed to be.