Any requirement for box hieght?

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BKearney

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I have a situation where I am putting a 24"x24"x10"deep NEMA 13 (I think) electrical enclosures on top of some plenums. One box per plenum. The electrical enclosure will hold a disconect (molded case circuit breaker), frequency controller for a fan, etc..

We are required to mount these boxes on top of the walkable plenums. In essence the walkable plenum top becomes a floor, even though its not a common trafic area. Initial discussions were to mount the box with the door swinging upward. But something kept nagging at me that it was a "no no" to do that. I kept thinking that the box needed to be mounted upright so that the door swung outward, and it needed to be mounted above the floor (ceiling of the plenum) several feet.

My questions are:

1) Are there any regulations or codes about disconnect boxes being mounted with the doors swinging upward versus outward?
2) IS there a hieght requirement for the bottom of the box if the box is mounted so the door swings outward?

I have snooped around NEC a bit, but I cannot find anything yet.

Thanks in advance for your comments!
 
BK,

I am only aware of Section 240.24(A)(4) which says Overcurrent protection devices located next to equipment they supply can be accessible by portable means. See 404.8(A) Ex. 2

At 404.8(A) ex.2 is states and allows for switches and circuit breakers used as switches can be mounted higher than 6' 7" if they are next to the equipment they supply and are accessible by portable means.

Might be someone stance that face up would possibly be inverted as opposed to being the allowable horizontal if it only has (1) circuit breaker...otherwise it would need to be mounted vertically ( 240.33)

But I dont think that may come into play....but again thats me.....I am sure Bob or Tom whom are probably much more knowledgeable on that than me will comment....:)
 
If it has a variable frequency drive in the panel, I would think that if the door swings upward, the sides of the panel would be in the required working space. So I think 110.26 would require the panel to be mounted upright.
 
Just to clarify, the frequency controller would be mounted inside the box, not on the door.

The other odd thing about this job that I failed to mention, is that these plenums are meant to be fitted together several at a time such that the air flows downward (and my box door would in this case swing upward) over a large area, however, there are going to be some casses when the owner is going to take these plenums turn thier orientation such that they are laying down and the air will blow side ways (and in this case my box would open like any box hung on a wall).

I am not sure (they wont tell me or dont know themselves) which plenum orientation will be most common.

From all the comments, I searched around a bit more in the mentioned sections, and I feel that as long as I ensure 3' above or in front of the door as it swings open then I am ok.
 
I have never thought about it before, but I don't think the working space can be 3' above the panel. For example, if you lay a VFD on its back, the 3' is still to one side of the VFD (which side, I don't know). It is not 3' above the VFD.

Or maybe I am alone in this line of thought?

One other thing: are you sure you can mount this cabinet in a plenum? It sounds like this is going in an air handling duct. Just enclosing a device in a metal panel does not make it OK to install in a plenum. In general, the VFD and the breakers would have to be plenum rated.
 
BKearney,

JMO. Laying the vfd on it's back might impede the heat shedding ability

also,if there are any contactors involved they will always be pushing down,

upon release if it rebounds downwards it will arc and spark pretty good.

Just a couple of thoughts thrown your way.
 
The box is mounted on unistrut attached to the outside of the pleunum...likely the box will be NEMA 12 or 13 I think...

The walkable top of the plenum has a prefilter box in the center of it with three 24x24 filters. We were planning on making a unistrut frame above the center filter (so you can still remove the filter and airflow is not restricted) such the the box would lay down above the center filter.

This situation is lose-lose no mater which way I position the box because they are going to use quick connectes for thier electrical connection and they will be rotating the plenums between downward airflow (box opening upward) and airflow horizontally across a room with the plenum laying on its side (and in this case the box opens like any normal box hung on a wall).

At this point I think I am most concerned with component functionality laying down versus upright as some mentioned above (i.e. heat sink on a freq drive or contactors sparking, etc.)...


Thanks for the comments!
 
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