NEMA Lug Connection to Medium Voltage Bus

[FaradayFF]

Hey All,
Are there any best practices or guidance that can be found when landing a MV cable with NEMA 2 hole lug on a medium voltage un-insulated bus bar? Should the copper bus be pretreated with a No-Ox compound and the lug installed perpendicular to the bus? Are there any issues with a portion of the insulated cable touching the bus?
My understanding is that we want to avoid drilling extra holes in the bus.

Thanks for your feedback.
EE

 

[paulengr]

Hey All,
Are there any best practices or guidance that can be found when landing a MV cable with NEMA 2 hole lug on a medium voltage un-insulated bus bar? Should the copper bus be pretreated with a No-Ox compound and the lug installed perpendicular to the bus? Are there any issues with a portion of the insulated cable touching the bus?
My understanding is that we want to avoid drilling extra holes in the bus.

Thanks for your feedback.
EE

Not so much noalox in particular but which one? You want electrical joint compound if anything. And it’s not how many holes but they need to be in line (rows and columns) not zig zag and don’t cut out more than if I remember 40% of the total width. The copper institute has a whole guideline on this.

When it comes to “insulation” there are two kinds of MV cable. Shielded should have a termination kit installed. In area where the stress grading is going on obviously it defeats the purpose if it’s laying against an energized bus bar or the shielded jacket is laying against uninsulated bus. A little bit of silicone sleeving down by the lug won’t make a difference. Best to connect lugs at an end or perpendicular to the long axis of the bus or buy 90 degree lugs and land that way. On unshielded cable you can of course treat it like low voltage and lay against the bus if the same phase. Otherwise it would be an area of high stress. All this is pretty basic and known to any MV installer so don’t try doing this on your own. Like any installation job there is a lot of “cut to fit” that goes on but if you spend a modest amount of time planning routing to avoid high stresses (unshielded or bare cables or bus or anything grounded) touching opposite phases or a ground/neutral it’s very straightforward. If not you may have problems in the future. Remember that an electron creates a mirror image charge in any nearby conductor and that excessive voltage flux can and will break down cables. If you avoid that condition you will be trouble free.