bonding raceway

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Electron_Sam78

Electron_Sam78

Senior Member
Location
Palm Bay, FL
250.97 talks about bonding metal raceway for 250+ volts but what about bonding raceway for voltages under 250 V? According to 250.96 it only needs it if the conduit will serve as a grounding conductor? So bonding bushings aren't need in a 120/240 V panel if the circuits all have grounding conductors run in the conduit? I've always installed the bushings but the code seems to say I don't have to. Is that right or am I missing something elsewhere?
 
Buck Parrish

Buck Parrish

Senior Member
Location
NC & IN
Electron_Sam78 said:
250.97 talks about bonding metal raceway for 250+ volts but what about bonding raceway for voltages under 250 V? According to 250.96 it only needs it if the conduit will serve as a grounding conductor? So bonding bushings aren't need in a 120/240 V panel if the circuits all have grounding conductors run in the conduit? I've always installed the bushings but the code seems to say I don't have to. Is that right or am I missing something elsewhere?
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As long as your locknuts are approved for bonding the race way it self. And you do not have eccentric knockouts. Grd. bushings are not required.
 
M

mweaver

Senior Member
Bonding of ALL raceways, enclosures etc.

Bonding of ALL raceways, enclosures etc.

Electron Sam78 asks:
250.97 talks about bonding metal raceway for 250+ volts but what about bonding raceway for voltages under 250 V?


Bonding for ALL metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non-current-carrying parts, that are to serve as grounding conductors, with or without the use of supplementary equipment grounding conductors, is governed under Section 250.96(A). Section 250.97 has heightened requirements where said bonding is for over 250-volts.

Please note that Section 250.96(A) provides specific performance requirements which must be met to accomplish said bonding, which includes "ensuring electrical continuity and the capacity to conduct safely any fault current likely to be imposed". Knockouts, including both concentric and eccentric, other those recognized in the 2009 UL White book Section QCIT, have never been recognized for such bonding. Meaning additional bonding, to meet the performance requirements, may be necessary for such knockouts. Section 250.96(A) goes on to inform that: "Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or be connected by means of fittings designed so as to make such removal unnecessary." Be aware that no such fittings have ever been listed to make such removal unnecessary. Meaning: Enamel is NOT your friend?

I do hope this is helpful,

Mweaver
 
Electron_Sam78

Electron_Sam78

Senior Member
Location
Palm Bay, FL
so the 250.96 leaves it up to the installer to determine if the fault path is sufficiently in tact and the only guideline talks about paint, enamel or other coatings.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Electron_Sam78 said:
so the 250.96 leaves it up to the installer to determine if the fault path is sufficiently in tact and the only guideline talks about paint, enamel or other coatings.
Click to expand...

No, if you follow the code the fault path will be sufficient in all but the longest runs.

The code requires that the paint or enamel be removed or that the fitting cuts into the paint.
 
tom baker

tom baker

First Chief Moderator
Staff member
Location
Bremerton, Washington
The reason for 250.92 bonding on raceways for circuits over 250v to ground is a ground fault on a 277 volt system will develop 5 times the heat as a 120 volt fault. Use ohms law, 1 ohm ground fault on a 277v system develops a lot of heat! Concentric and Eccentric KOs can't withstand the heat. By the way, both soares and IEEE recommend bonding one end of a raceway with 277v conductors.
 
D

DesignElectric

Member
Location
Holiday Florida
Metal Raceway Bonding

Metal Raceway Bonding

Essentially guys, in my view, it's quite simple.
A bonding Locknut for systems under 250V to ground will be adaquate, rather than a bonding bushing.
 
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