Long direct burial feed to transformer

[petersonra]

After consulting with a utiltity line-foreman, I was told that 250-300 ft was an average length between poles for 21K. (275'). So my 6000 ft run wold take (6000/275) 22 poles + 1 end pole. 23 poles @ 10K per pole = $230,000 for the pole line extension; $38 per foot.

OK my new question is "Can you run 500+MCM UF for $38 a foot"?

Can you even get UF that large?

You probably cannot trench in PVC for that kind of money.

 

[Fulthrotl]

A customer is asking me to design and provide cost estimates for a direct burial 480 volt single phase feed to a transformer at the other end that will provide 120/240 single phase power to a building. The run is to be several thousand feet on this rural ranch setting. We are estimating the secondary load to be around 50 amps @ 120/240V. Voltage drop calulations are pretty cut and dried using one of several wire mfgs Vd charts. I realize that large conductors would be needed. A typical installation would be to run 2 480V current carrying conductors (l1,L2) and an equipment carrying conductor. At the transformer at the out building, a ground rod or similar electrode would be installed and that would be bonded to the nuetral of the secondary of the newly created 120/240V system.

However, is there a safe way of eliminating the EGC that would normally be run with the 480 volt feed (for cost issues)? Maybe an isolation transformer on the feed side. I know that under normal circumstances that simply driving a ground rod at the far end and bonding to secondary neutral will do little to clear a 480 volt fault if no grounded conductor is installed. The earth is not that great a conductor. Kind of like driving a ground rod attempting ground metal light poles to clear a fault-virtually useless (except for lightning).

I am not advocating eliminating the EGC. I normally run EGC with everthing, especially in the smaller sizes. Just wondering if a SAFE alternative would work. I pretty much already know the probable answer. We also might consider medium voltage (4160).

for what this is gonna cost you, i'd look at using your natural gas option with
a stationary genset, driving a battery bank thru an inverter/charger.....
the genset will cycle to keep the batteries up, so it won't be a 24/7 deal.

now, this is somewhere i'd also look at tossing PV's up on the roof, to cut
the generator run time. also, this gives you some standby time for genset
servicing and whatnot.

6k feet of 750 al UF cable 36" deep is gonna be a big expense, and then
you have the "what if you have a cable fault in two years?" sort of issue...

however..... IF you are putting a gas line in to the location, and can colocate
the cable at 48", and the gas line shaded in at 36"..... as long as you have
a ditch anyway..... and the gas line is plastic, so you don't have induction....

and bumping it up to 575 and back down to 240 might save you some wire
size...