Medium Voltage Switchgear - Bus Tap

[pgonski]

I have a project where the client has no room in the 4160V switchgear for any additional cubicles, and the transformer powering it connects via nonseg bus duct.

The question of whether or not we can perform a cable tap onto the switchgear bus has been asked, and I have never seen this being done before.

Any opinions on whether this is an option? I know the tap rules, etc..........but I have never seen this applied to a 4160V switchgear bus.

 

[ron]

I don't see why it would be any different than 480V gear, as long as you don't violate any spacing or listing requirements. It is likely best to work it out with the SWGR manuf

 

[greenspark1]

Never heard of it either. Let us know what the switchgear manufacturer says.

 

[pgonski]

Never heard of it either. Let us know what the switchgear manufacturer says.

The answer is you can not do so without voiding UL listing

 

[MasterTheNEC]

You will need to contact the manufacturer of the gear and ask them directly. There are specific areas within the buss that manufacturers usually permit tapping but doing so without manufacturers guidance will serve two functions...remove any warranty or liability the manufacturer assumed with its production and you will remove it's listings from its original evaluation. It is not a matter of IF you can tap the buss since we all know its physically possible....but that does not make it legal or compliant.

Again the manufacturer knows their product better than anyone so contact them and run the situation across their desk. The local AHJ may also require a 3rd party NRTL investigation/evaluation once the tap is completed (provided the manufacturer says its ok and where it has to be done).

 

[SG-1]

The answer is you can not do so without voiding UL listing

Is there any room at either end for something like a transformer throat assembly? The bus could be extended in the usual manner into a cable tap box configuration. This would not have to be nearly as wide as a normal cubical.

If the switchgear is metalclad it may present some barriers to tapping into the main bus in the existing structures. When your done it may no longer be listed or metalclad.

 

[philly]

I just came across a similar situation where this was being considered and wandering the same thing from a practically and compliance standpoint.

From a practicality standpoint I realize this can be easier said than done depending on bus construction. Interesting to see comments above with regards to warranty and UL listings.

I also came across NEC 240.101(B) which appears to reference feeder taps above 1000V and indicates that the feeder tap cannot be reduced in size and thus must carry the same rating of the feeder which it is tapping? I'm assuming this would also apply to tapping Switchgear? In this case if tapping a 3000A bus to feed a separate 1200A feeder structure the tap would still need to have an ampacity of 3000A (regardless of distance).