Mark Twenhafel

I'm up to Art. 250 in the code and have a general question about the terms "System Bonding Jumper" as used in 250.28 and 250.30. In fact, the title of Article 250.28 is Main Bonding Jumper and System Bonding Jumper.

Thing is, the term System Bonding Jumper isn't defined in Art. 100, near at least as I could find. The term Main Bonding Jumper is defined in Art. 100. Main Bonding Jumper is defined as the "connection between the grounded circuit conductor and the equipment grounding conductor at the service."

This got me to thinking in terms of the service vs. the system.

Here's what I'm asking: If the Main Bonding Jumper connects the grounded conductor (neutral) and the equipment grounding conductor (ground) between the load side of the service drop (or lateral) and the line side of the service disconnect, then does the System Bonding Jumper connect the same conductors for the system, specifically between the load side of the main disconnect (like in a residential main panelboard that is not an all-in-one) and the branch circuit breakers.

So, would it make sense to change the code to refer to Service Bonding Jumpers and System Bonding Jumpers--where they both do the same thing, but one is in the service equipment and the other is in the system equipment?

Or, am I all wet? (All of my experience so far is residential, so I may be missing something that would be obvious with more commercial or industrial experience.)

Just askin',
Thanks,
Mark

wayni

The Main Bonding Jumper is installed at the service. You'll always have one, no more no less.

System bonding jumpers are those installed at separately derived systems. You'll have one, no more no less, for each separately derived system utilized.

Both serve the same purpose. Both provide an effective ground fault current path from your equipment enclosures, raceways, EGCs to the source, needed to ensure proper function of your breakers and fuses.

Mark Twenhafel

Thanks. I'm thinking I need to branch our from the code to some Delmar books. Thanks, again.

HARRY MILLER

At a service there will be one main bonding jumper in each separate main disconnect enclosure from the grounded conductor to the grounding bar or enclosure. If there are 6 separate main disc. enclosures there will be 6 main bonding jumpers. Similarly there must be an unspliced system bonding jumper connected from the grounded conductor to the equipment grounding conductors of the separately derived system. Equipment grounding conductors of a separately derived system originate in the first enclosure with overcurrent protection (any bonding/grounding conductors on the supply side of OCP are equipment bonding jumpers) The difference from connections at a service is that this connection from the EGC's to the the grounded conductor can be made anywhere from the enclosure with the first overcurrent back to the source "xo", but one end of the system bonding jumper will be connected to the grounding bar in the first enclosure with overcurrent protection. See NEC Handbook 2005 or 2008 in article 250.30, exhibit 250.13 and exhibit 250.14 for proper connections at a separately derived system. There are many inaccurate drawings out there. These exhibits are the only drawings that totally agree with the language of the code. If there are 2 separate enclosures with OCP fed by separately derived phase conductors there will be 2 system bonding jumpers etc. sincerely - Harry Miller