Tap question 240.21(B)(1)(4)...metal clad switchgear...leave the enclosure?

[Dweeber]

All,

Let me attempt to describe what I have: a metal clad enclosed switchgear, with added on SPD (TVSS). The device is enclosed in it's own box, mounted to the exterior surface of the switchgear. A very short chase of rigid conduit with bushings allow the tap conductors that are lugged to the copper busses to terminate in the TVSS.

The TVSS has some small 30 amp fuses internally, and the tap conductors are 4 awg, if that matters. The bus is 480v 3 phase with the main bus rated at a capacity of 4000 amps.

These taps are short in length, less than 5 feet. My question is, does this qualify as "leave the enclosure"?

I referenced 2008 240.21(B)(1)(4). Thanks in advance,

D.

 

[petersonra]

All,

Let me attempt to describe what I have: a metal clad enclosed switchgear, with added on SPD (TVSS). The device is enclosed in it's own box, mounted to the exterior surface of the switchgear. A very short chase of rigid conduit with bushings allow the tap conductors that are lugged to the copper busses to terminate in the TVSS.

The TVSS has some small 30 amp fuses internally, and the tap conductors are 4 awg, if that matters. The bus is 480v 3 phase with the main bus rated at a capacity of 4000 amps.

These taps are short in length, less than 5 feet. My question is, does this qualify as "leave the enclosure"?

I referenced 2008 240.21(B)(1)(4). Thanks in advance,

D.

IMO, they do indeed leave the enclosure.

Where did they find 30A fuse holders that will take #4 conductors?

One might argue that if the SPD enclosure is permanently bolted to the switchgear it is effectively part of the switchgear. Did it come that way from the manufacturer of the switchgear? or did someone add it in the field?

 

[Dweeber]

Petersonra,

The 4 awg conductors terminate on a lug, that lug is bolted to a small bus bar inside the TVSS, fron that busbar are the fuses that go to the electronics in the TVSS.

The TVSS is bolted to and supported by the exterior sheet metal of the switchgear.

I hope that helps in describing this particular installation. The TVSS was added to the switchgear, not the same brand even. I am thinking as-is, the the addition of the TVSS leaves the enclosure.

What if the entire back of the TVSS was open and a large opening was made to accomodate the conductors, and eliminate the rigid conduit entirely?

Just trying to sort through this.

D.

 

[petersonra]

Petersonra,

The 4 awg conductors terminate on a lug, that lug is bolted to a small bus bar inside the TVSS, fron that busbar are the fuses that go to the electronics in the TVSS.

Are there wires going from the bus bar to the fuses? If so, they are not legal taps IMO.

The TVSS is bolted to and supported by the exterior sheet metal of the switchgear.

I hope that helps in describing this particular installation. The TVSS was added to the switchgear, not the same brand even. I am thinking as-is, the the addition of the TVSS leaves the enclosure.

What if the entire back of the TVSS was open and a large opening was made to accomodate the conductors, and eliminate the rigid conduit entirely?

Does not deal with the illegal tap issue as the conductors still leave the enclosure. I don't think the route by which it leaves matters much.

Just trying to sort through this.

D.

To be candid, I don't see this as anything worth worrying a whole lot about. if there is some reason you feel the need to "fix" this, the simplest solution is probably to replace the #4 wire with the largest size wire that will fit on the fuse blocks and move the fuse blocks inside the switchgear enclosure. you might even be able to find a spot inside the switchgear for the whole SPD assembly.

 

[weressl]

IMO, they do indeed leave the enclosure.

Where did they find 30A fuse holders that will take #4 conductors?

One might argue that if the SPD enclosure is permanently bolted to the switchgear it is effectively part of the switchgear. Did it come that way from the manufacturer of the switchgear? or did someone add it in the field?

How about the fault withstand rating? Switchgears are commonly rated 65kA and above.