Conduit Clearance/Switchboard

[augie47]

Can anyone advise on the reasoning behind the 3" max. height give in 408.5 ? I understand the 8" or 10" clearnce for bussbars, but fail to see the reasoning for the 3" limitation. I know my job is to enforce the Code, but everytime this violation arises, I get a world of "whys" and I am curious myslef.

Edit: correct typo

 

[don_resqcapt19]

I assume, the 3" maximum is to make sure that there is wire bending space above the conduit.
Don

 

[augie47]

My first thoughts, but 408.3(F) and the 408.5 Table pretty well take care of that.

 

[charlie b]

I can't give you an answer that is anything more than a guess. But I think that "why 3 inches?" is the wrong question. The right question is, "Why is there a limitation at all?" Once you are comfortable with the need for a limit to exist, then it becomes a matter of "3 inches is as good a limit as any other, since it gives enough room for XXX, and since it is not too much for XXX."

I can only guess that a limit is there to prevent the conduit from being so high that you won't have room to manipulate the incoming cables into their positions (i.e., a bending radius problem).

 

[infinity]

IMO this is a good example of bad code. For almost every entry that I've seen into the bottom of an open switchboard with EMT, the conduit is supported by a piece of strut with a strap, a connector, and a bonding bushing. For a larger size conduit this would bring the top of the entry to a height far greater then 3" above the floor. If the bending radius is a problem, well, that has been outlined elsewhere in the code. A set distance from a buss bar, is also a good idea but this has little to do with the 3" limitation. I'm not saying that there shouldn't be a limit, but 3" is impractical and most of the time impossible to obtain.