Maximum Run Length for 277/480V Underground Feeder

[Rawright54]

I've done a lot of long runs with MV lines, but the customer wants to use an existing 6" conduit for this circuit, and it's 1500' long! The math works out for a 120A circuit such that 350 mcm Al THWN-2 class B cable should do the job, but I've never run 480 that far. Is there a practical limit to how far I can stretch this?

 

[augie47]

It all comes down to $$. You just need to price your options. Will the utility provide a service to the building and at what cost....will the utility provide you with MV or would you need transformerS.... The last time I saw 350 priced I guess u are looking at $5 a ft going that route

 

[Rawright54]

I priced it today online, and it was $2.60/ft for 5000'. In this case, I am the utility, since I manage the microgrid they want to extend to a new facility. I'm just wondering if there's any gotchas that come with extremely .long runs of LV line. I'm more used to designing 69kV, 25kV and such than 480. If I go the primary route at 20.8kV, I've got the cable on hand, but then there's going to be new conduit, new switchgear, and a new pad-mount transformer with its cost and ridiculous lead times.

 

[ptonsparky]

1500+- ft is done often enough for irrigation wells. Should be no problem.

 

[Rawright54]

Thanks, both of you, for the input!

 

[LarryFine]

The higher the voltage, the better, usually.

 

[electrofelon]

I've done a lot of long runs with MV lines, but the customer wants to use an existing 6" conduit for this circuit, and it's 1500' long! The math works out for a 120A circuit such that 350 mcm Al THWN-2 class B cable should do the job, but I've never run 480 that far. Is there a practical limit to how far I can stretch this?

I don't consider 1500' that far and usually at that length it's not worth messing with transformers or MV.