Bushing or no bushing? Voltage is 480

ctaylo360860

Senior Member
Location
colorado
Occupation
ME
Inspector says I can’t use exception 3 or 4 in 250.97 because I’m using liquid tight flexible metal conduit.
Race way has wire type egc and ul listed fitting with a shoulder is seated to the box. It’s going into a concentric hole.
Even then the bushing would only bond the raceway if the connector is connected with the lock but and the fitting that secures the raceway to the connector.
Bonding bushing only hits the threads on the connector if lock button isn’t tight it’s not making a good connection. What you guys say?!
 

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Carultch

Senior Member
Location
Massachusetts
The issue is that the narrow connections between the ring knockouts are a choke-point in the grounding path that is "not strong enough" for a fault driven by over 250V to ground, unless the box is specifically listed for bonding at a higher voltage (e.g. 4S boxes that have heavy duty knockouts).

If you use up all of the ring knockouts at a particular conduit entry or enter at your own punched hole in the box, you get to treat it as if the ring knockouts were never there in the first place. It is when the knockout rings remain at the entry in question, that this rule applies. I cannot see from the photo whether the conduit entry in question has used up all the knockout rings or not.

The reason we attach a bonding bushing is to enable the connection of a bonding jumper between its lug and the grounding terminal of the equipment. Just installing a bonding bushing isn't enough.
 

ctaylo360860

Senior Member
Location
colorado
Occupation
ME
I understand a 4 square box wouldn’t require bonding bushings. But it seems silly to me to have to use one in a concentric hole…. But by golly if it’s code I guess I’ll have to find some more 1/2 bonding bushings to be compliant. ….
 

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infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I don't believe that any cabinets or enclosures other than specific Article 314 boxes meet the suitable for bonding over 250 volts requirement. Disconnect switches do not. Based on the photo in post #5 I agree with the inspector.
 
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