BOND FRAME OR BUSHING IS ADEQUITE?

[VALZ]

Hello all,

I was wondering if anyone can put this issue to bed for me in direct code reference terms. I have searched the forums and could not find this direct question... Disconnects, fused and non fused. Should the frames be independently bonded with a "lug" or "terminal bar" to the frame even if the disconnect has a bonding bushing located inside of it with the ground properly attached to the bonding bushing lug. And or in a fused disconnect with a bonding screw in place bonding the neutral to the ground. In my opinion, yes, even if the disconnect has a bonding bushing and a bonding screw neu/grd(fused disct) it should also have a mechanical attachment directly to the frame.

I have referenced... 408.40 Grounding of Panelboards. Panelboard cabinets and panelboard frames, if of metal, shall be in physical contact with each other and shall be connected to an equipment grounding conductor. Where the panelboard is used with nonmetallic raceway or cable or where separate equipment grounding conductors are provided, a terminal bar for the equipment grounding conductors shall be secured inside the cabinet. The terminal bar shall be bonded to the cabinet and panelboard frame, if of metal; otherwise it shall be connected to the equipment grounding conductor that is run with the conductors feeding the panelboard.

and then...Panelboard. A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front.

I have been always under the impression that a bonding bushing bonds "the conduit to the frame" and the bonding screw bonds the "neutral to ground", none of which I believe are a direct purpose to bonding the frame for the sake of bonding the frame.

If I am wrong on any of these accounts please inform me, if I am correct please inform me as well. Either way anyone who knows a direct code reference to either call out a violation or understand that it is safe and passable please let me know.

Thank you all very much!

"BY THE TIME I'M 90 I MAY KNOW ENOUGH TO CONSIDER MY SELF AN ELECTRICIAN"

 

[Carultch]

A bonding bushing bonds the conduit to the bonding jumper. I.e. it allows you to make the conduit electrically continuous with wherever you connect the attached wire. Bonding bushings do not necessarily connect the enclosure to the raceway electrically, unless the other end of the jumper is attached to a lug that is electrically continuous with the enclosure. Or if you have a bushing/locknut combination fitting.

In the simple case, the locknut makes the metal conduit electrically continuous with the metal enclosure. Locknuts also serve a mechanical continuity purpose as well. More substantial means such as a bonding bushing might be needed, depending on the application specifics. Examples are service conductor raceways, grounding electrode conductors, and ring knockouts remaining in applications greater than 250V to ground. See 250.97.

A grounding busbar, lug, kit, or other assembly of wire terminals, is another place to bond the enclosure, and you will commonly find these for panelboards and disconnects. This is where you'd attach the bonding jumper of a bonding fitting (bonding bushing, bonding locknut, bonding wedge, etc), and where you'd connect the EGC to the various other devices that are part of the system.

 

[VALZ]

Agreed, but by having solely a bonding bushing with or without a locknut, will that provide the necessary protection and or grounding of the frame instead of using a lug kit. Basically I am seeing disconnects being installed with only bonding bushings and having other electricians state that by having the bonding bushings on is the same as having a lug kit installed to the frame.

 

[electrofelon]

Agreed, but by having solely a bonding bushing with or without a locknut, will that provide the necessary protection and or grounding of the frame instead of using a lug kit......

No. Read Carultch's response again:

A bonding bushing bonds the conduit to the bonding jumper. I.e. it allows you to make the conduit electrically continuous with wherever you connect the attached wire. Bonding bushings do not necessarily connect the enclosure to the raceway electrically, unless the other end of the jumper is attached to a lug that is electrically continuous with the enclosure. Or if you have a bushing/locknut combination fitting.

 

[iwire]

You can use a bonding bushing without a locknut.

See this from 300.4(G)

Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway.

 

[Carultch]

You can use a bonding bushing without a locknut.

See this from 300.4(G)

Mechanically or electrically?

I understand using a bonding bushing without a locknut mechanically, especially when there is not enough thread on the fitting to fit both fittings. Because a threaded bonding bushing still is a nut, and tightening in the second setscrew gives it its locking in place. But it doesn't have any teeth to dig in to the enclosure wall, to establish electrical continuity to the enclosure.

 

[iwire]

Mechanically or electrically?

I understand using a bonding bushing without a locknut mechanically, especially when there is not enough thread on the fitting to fit both fittings. Because a threaded bonding bushing still is a nut, and tightening in the second setscrew gives it its locking in place. But it doesn't have any teeth to dig in to the enclosure wall, to establish electrical continuity to the enclosure.

There is no reason it has to bite into the enclosure, the entire point of the bonding bushing is to give us a place to put a wire jumper in place from the conduit to the enclosure.

Also, we have to comply with 250.12.

 

[Carultch]

There is no reason it has to bite into the enclosure, the entire point of the bonding bushing is to give us a place to put a wire jumper in place from the conduit to the enclosure.

Also, we have to comply with 250.12.

My point is, if you don't attach the wire to a lug elsewhere that is electrically continuous with the enclosure, the bonding bushing doesn't make electrical continuity with the enclosure on its own. Not without a locknut in the same fitting stack, or a bonding jumper to an enclosure connected lug.


EDIT: Ok I just read 250.12, and I see what you mean.

 

[VALZ]

So with my original understanding the bonding bushing bonds the conduit to the frame "regarding 250.12". so then I am still to believe that the frame needs an independent lug to bond the frame solely. in conjunction with a bonding bushing. Agree or disagree?

 

[iwire]

My point is, if you don't attach the wire to a lug elsewhere that is electrically continuous with the enclosure, the bonding bushing doesn't make electrical continuity with the enclosure on its own.

If you are installing bonding bushing for the purposes of bonding you must connect a wire to the lug and the enclosure. No wire jumper should result in a failed inspection.