Bonding vs Grounding 2

[insitebuilders]

Disclosure, I'm an architect (yes I know, that says it all...;-)

I noticed in the NEC that bonding jumpers are required between the *metal* boxes, raceways, etc to provide GF continuity. I've also noticed them on some jobs, but not all. I can't figure out if this secondary GF path is always required or just necessary when using a metal system... For example, not required if PVC conduit/boxes are used. Perhaps they are only req'd for certain Bldg Types?

One thought is that the bare copper wire found in most elec cable somehow preclude this jumper system since it seems integral w/ the entire grounding system (and does not seem to be coverd in the NEC. But that's only an "aesthetic" observation.

Can anyone clarify this for me please?

Thx

Dennis

 

[dpc]

Steel conduits, if installed correctly, can suffice as a grounding connection, per the NEC. Other raceways don't qualify as a grounding conductor and a separate jumper is required. Or not. Take a look at Article 250 in the NEC after you've had a couple of martinis.

Besides, we intentionally make it complicated for job security.

Anything metal that might become energized has to be grounded for safety reasons.

 

[insitebuilders]

Thanks, I thk I get it. Especially with motor controls and other direct circuits

But it seems like if there is/was a bare copper wire in addition to neutral in a 3or4 wire cable bundle, it'd be acting as the GF path to ground anyway. Are these bare grounding wires not used in some cases for some reasons?

/D

 

[SteveWag]

The Code requires all metal used in the construction of a wiring system to be bonded to, or connected to the ground system. In a system using a non-metallic wiring system, NM cable (romex) or PVC conduit for example, a bonding conductor, bare or insulated is carried with all other conductors, in the cable or conduit, and this conductor must be fastened to any metal it passes through and to and to the grounding terminal of all outlets. If a metallic wiring system is used; EMT, rigid conduit, either steel or aluminum, some trays, or cable type AC, the system can be used as the bonding system. If you look at a standard duplex outlet, you can see that the grounding screw is connected the screw holes that mount the outlet strap to the box. This means the outlet is automatically grounded when the screws are tightened to a metallic box that is a part of an approved metallic bonding system. (The reverse is not true; the strap cannot be used as a way of bonding the box.) As dpc says, we intentionally make it complicated for job security.
Steve Wagner

 

[insitebuilders]

.
DCP/Steve

Thx, I reread NEC 250 and found it interestg that so much of the 2005 is devoted to this subj and so little clarifies use of non metallic raceways. But I see now why the bare wire is used or not used and of course the importance of the GF path when a potential fault might occur w/ metal. I haven't seen a lot of PVC/non-metal on commercial proj but was curious.

Thx again for the clarification.

/Dennis