Can Fused Disconnect Switch Enclosure be mounted in a Pullbox?

[vhoa]

Is it against NEC code for installing a 480V , 3 phases -Fused disconnect switch inside a pullbox?

 

[augie47]

IMO, it might come down to accessibility. 404.8 requires switches to be located so they can be operated from a readily accessible place.
How would one access the switch ?

 

[jumper]

I will through in working clearances also. 110.26

 

[Jraef]

I cannot think of a fused disconnect that COULD be mounted in a pull box anyway. Or are you thinking of using one of those cheap little UL508 rated rotary through-the-door type? If so, are you using it correctly? There are some restrictions to using those, the kind the salesmen never tell you about...

 

[vhoa]

Thank you for your reply.
The Fused Disconnect used in our design is only to limit available fault current to our existing 480V panelboard, which is rated at 10KAIC and has no main breaker. The panelboard is fed from a 200A feeder breaker in our switchgear lineup in the next room. The fused disconnect is NOT to be used as a disconnecting mean.
BACKGROUND: Due to recent transformer upgrade, the 3 phase fault current at the input of the panelboard is now about 25KAIC. With the use of current limiting fuses installed in front of the panelboard, the fault current could be limited to about 5KAIC.
Fused disconnect is a surplus from our store, so we want to use it. The pull box I refer to is a 48" x 48" x 72" cabinet, which has been used only for routing of two 480V feeder circuits to 2 MCCs- (3) 350MCM/circuit. So it is quite empty in this so called "pull box'.
Due to no space available for mounting the Fused disconnect, we are thinking installing it inside the "pull box", which is right next to the 480V panelboard.

So the ultimate question is: Can we install overcurrent protection device inside the pull box if all clearances are met? Would it be any different if we just install fuse blocks inside an enclosure - with no operating mechanism, and mount the enclosure inside the pull box.

We could not find any sections in the NEC Code that say we CAN'T do it, but we know is NOT a good practice

I cannot think of a fused disconnect that COULD be mounted in a pull box anyway. Or are you thinking of using one of those cheap little UL508 rated rotary through-the-door type? If so, are you using it correctly? There are some restrictions to using those, the kind the salesmen never tell you about...

 

[Jraef]

The Fused Disconnect used in our design is only to limit available fault current to our existing 480V panelboard, which is rated at 10KAIC and has no main breaker. The panelboard is fed from a 200A feeder breaker in our switchgear lineup in the next room. The fused disconnect is NOT to be used as a disconnecting mean.

This might turn out to be a more immediate problem before you even get to the fused disconnect part. Where is this concept coming from? Is there a PE involved?

 

[hbendillo]

Where is the pull box physically installed in the circuit? Are you talking an underground pullbox? A pullbox in an electrical room next to the panelboard? On a wall outside?

 

[GoldDigger]

Depending on the location, there might be a problem with working space at the front of the fused disconnect. If it comes close to the front face of the pullbox that might minimize any problems, but access to the pullbox will then come into play.

 

[don_resqcapt19]

Is the disconnect one that is required to be readily accessible? If the pull box cover requires the use of a tool to open it, the disconnect is not readily accessible. (2104 NEC)

 

[ron]

This might turn out to be a more immediate problem before you even get to the fused disconnect part. Where is this concept coming from? Is there a PE involved?

Agreed. If you are using the current limiting curves from the fuse manufacturer without having actual series ratings for all of the downstream combinations of equipment, it might be a non-starter.

 

[vhoa]

The pull box I refer to is a 48" x 48" x 72" cabinet, which has been used only for routing of two 480V feeder circuits to 2 MCCs- (3) 350MCM/circuit. It is above ground and sits next to the panel inside the electrical room.

Where is the pull box physically installed in the circuit? Are you talking an underground pullbox? A pullbox in an electrical room next to the panelboard? On a wall outside?

 

[vhoa]

Yes, PE is involved. It is quite a common engineering solution to use CLF to limit available fault current - thus "increasing" the rating of the panelboard.

This might turn out to be a more immediate problem before you even get to the fused disconnect part. Where is this concept coming from? Is there a PE involved?

 

[vhoa]

I accidentally left out the rating of the 480 V panel is 10kAIC in the background info in the response to Jraef's comment. the CLF limits the fault current to about 4 kAIC.
so what I want to know is "Can we install overcurrent protection device inside the above ground pull box if all clearances are met?"

Agreed. If you are using the current limiting curves from the fuse manufacturer without having actual series ratings for all of the downstream combinations of equipment, it might be a non-starter.

 

[ron]

I accidentally left out the rating of the 480 V panel is 10kAIC in the background info in the response to Jraef's comment. the CLF limits the fault current to about 4 kAIC.
so what I want to know is "Can we install overcurrent protection device inside the above ground pull box if all clearances are met?"

Other than very particular criteria, you cannot consider the CLF limiting the fault current . You need an actual tested combination (series rating)