conductors

[mightyjoe]

Is it permissible to route a neutral conductor in a nonferrous raceway.
Existing 3 phase 4 wire, but the buss duct to hvac equipment is 3 phase 3 wire. New equipment requires a neutral connection. Looking at 300.3 trying to figure out options. Looks to me like a xfmr at each equipment room,or distribution in place of buss duct and refeed to each floor.

 

[Dennis Alwon]

If it is non ferrous and complies with 300.3(B)(3) I believe you are okay but you will create unwanted emf's.

 

[don_resqcapt19]

I am sure that the bus in the bus duct is within a ferrous enclosure, so there is no code compliant way to run a neutral conductor in a seperate raceway.

 

[Dennis Alwon]

I am sure that the bus in the bus duct is within a ferrous enclosure, so there is no code compliant way to run a neutral conductor in a seperate raceway.

Good catch- missed that bus duct.

 

[Smart $]

The neutral conductor would have to be within the same bus duct as the line busses.

The neutral is permitted to be of a lower ampacity (i.e. smaller) than the line conductors, but contingent on load and grounding equivalency. Is it permissable to run a wire neutral conductor inside a bus duct? I don't see any explicit restriction in Article 368... but I guess if a wire conductor is installed, the duct would no longer be a busway, since the wire is not factory mounted (368.2).

What about installing a delta-wye transformer on each floor? This would eliminate the need to refeed each floor, as the neutral grounding typically would be made to local building steel. Even if the GES/GEC has to be run to the main distribution, service equipment area, it can be separate to the bus duct(s).

 

[ZZDoug]

What about installing a delta-wye transformer on each floor?

Sometimes you get lucky and can just pull an extra wire in the conduit or tray etc. But in most cases where there is no neutral a transformer is the usual solution.