When to use grounding bushings?

[peter]

A holy jihad is about to develop between me and my infinite superior concerning the use of bonding bushings. All I have found is 250-94 (4) which refers to their use around concentric knockouts but the end of the paragraph says "required by this section" and the section refers to service equipment and such.

This issue seems to be at an outdoor disconnect box, 60 amps, to which LiquidTite is attached to a concentric knockout. This is not a service by any means. Is it necessary to use a grounding bushing here?

~Peter

 

[dave81]

Re: When to use grounding bushings?

I would say no but pull a seperate EGC to the disco.

 

[ryan_618]

Re: When to use grounding bushings?

Just out of curiosity, is this metallic or non-metallic sealtite?

 

[pierre]

Re: When to use grounding bushings?

Peter
try 250.96(A)

Although 'effectively bonded' is not defined in the NEC, it is generally understood that it means the connection is intentional and purposefully made.
One thing to remember ... a ground fault can produce a very large amount of current flow!!!

Pierre

 

[ryan_618]

Re: When to use grounding bushings?

Pierre: I think we're on the same page here.

 

[peter]

Re: When to use grounding bushings?

It's metalic liquid tite.
It's a 60 amp disconnect with three #6 wires and a #8 ground.

 

[pierre]

Re: When to use grounding bushings?

Peter
The concern for this installation is the metallic part of the liquid tite. If a fault occurs to the metallic part, is the connection to the enclosure good enough to permit enough fault current to flow to open the OCPD? In my opinion, if one tightens the locknut enough and the concentrics are not damaged during installation and the Liquidtite is secured properly, I would say it is fine.

Pierre

 

[iwire]

Re: When to use grounding bushings?

3/4", 1" and 1 1/4" Liquidtight can be used as a equipment grounding conductor for use with overcurrent devices rated not more than 60 amperes. 250.118(7)(c) for all the details.

IMO it would be hard to argue that this same liquidtight would need bonding for circuits less than 60 amps and are not service conductors.

 

[rhombus65]

Re: When to use grounding bushings?

If my memory serves me correctly you only need bonding bushings if the concentric or eccentric knockouts are not listed as being an adequate ground.

Most manufacturers do have their knockouts listed for grounding.

I can not remember the last time I used a bonding bushing and I have never failed an inspection as a result of not using one.