Adding bus bars to disconnect switch

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squeakapotamus

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Electrical Designer
I am specifying a new bolted pressure switch to be installed on an existing 480V, 1200A service entrance feeder. There is concern that the feeders will not reach the load side lugs on the new switch. The facility owner doesn't want to have new cables pulled because it will increase downtime. Instead, he has requested to have bus bars bolted to the load side of the switch, which will lower the lugs down toward the bottom of the enclosure. Even if everything were properly spaced, I'm concerned that there would be a conflict with the UL listing for the switch. Would I need to get the manufacturer to sign off on changing a switch? Would this qualify as a field modification that requires evaluation by UL?
 
petersonra said:
How is adding some bus bar any different than splicing on some wire to make it reach?
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It is different because when you are splicing wire, you are not making any changes to the switch itself. The solution the owner proposed is to unbolt the mechanical lugs from the switch and re-install them on a piece of connecting busbar. I feel like this could be considered a code violation if it goes against any instructions in the switch's listing or labeling, per 110.3(B).
 
squeakapotamus said:
It is different because when you are splicing wire, you are not making any changes to the switch itself. The solution the owner proposed is to unbolt the mechanical lugs from the switch and re-install them on a piece of connecting busbar. I feel like this could be considered a code violation if it goes against any instructions in the switch's listing or labeling, per 110.3(B).
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Reusing the lugs on the bus bar could be a problem if the lugs are not listed. I would probably not want to reuse the lugs anyway. I would just bolt on the bus bar extensions and bolt listed crimp on lugs to the bus bars.

Just out of curiosity how far off are you? You can extend the wires a few inches with pin connectors.
 
petersonra said:
Reusing the lugs on the bus bar could be a problem if the lugs are not listed. I would probably not want to reuse the lugs anyway. I would just bolt on the bus bar extensions and bolt listed crimp on lugs to the bus bars.

Just out of curiosity how far off are you? You can extend the wires a few inches with pin connectors.
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Chances are they will reach without any modifications, but we are developing a backup plan that can be quickly installed if they don't (time is money!)
I have considered the pin connectors but the ones I've seen are only about 2 inches long so I doubt they would help that much. It will be hard to know until it is installed, they're not gonna take an outage just so I can measure the cables.
 
is there room below the switch to mount a gutter? you could put some power distribution blocks there, terminate the old wires to the power blocks, and then run whatever wire lengths needs to be run up into the switch.
 
Bus bars need bracing, so yes, (in my opinion) adding them would be essentially modifying the disconnect in a way that itself is not UL listed, so would violate the UL listing on the switch, including the SCCR. So you could end up with an unlisted assembly that is only good for 5kA SCCR, which on a 1200A switch would be basically impossible to connect. It's also possible that by extending the connection point of the disconnect down further into the box, the "new" connection point will not meet the required wire bending space for the conductors. Manufacturers rarely give you extra space for no good reason. But ostensibly if this is being added to EXISTING gear, the wires were terminated on something that WAS within the required distance, so that may not be a problem.

If that's the case, you could possibly put stud distribution blocks below the disconnect and run cable or FlexiBus* between them and the disconnect lugs. But the SCCR issue may still be a problem because some of those distribution blocks have low SCCR ratings too. Marathon has one that is rated for 25kA, but that might still be an issue for a 1200A service.

* Because Flexibus is insulated, it does not need bracing, it's like cable in that aspect, but does not have wire bending space requirements like cable does. It is expensive compared to cable, but is the kind of thing that solves problems like this.
 
Dumb question but why not use crimp splices to extend the wire? If time > money you could even prep the extensions long and preinstall them to the new switch then you only have to crimp the extensions to the existing conductors.
 
I would prefer compression butt splices with heat shrink to extend the existing cables over adding bus bar.
 
Bus bar landing pads are commonly found on bolted pressure switches. If they are only a few inches, to maybe one foot, they may not need any bracing beyond a single rod. Of course, as others have pointed out, you need to be concerned with clearances. It is probably worth exploring with a company that does these types of modifications on a regular basis.
 
After talking with the switch manufacturer, they have no reservations or restrictions on landing bus bar on the bottom of the switch. Still, I don't want to over-complicate things so I think I will present some alternative solutions to the owner. I think the better option would be to add butt splices or a distribution block. The contractor can add cable or flexibus between the splice and the switch.
 
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