277/480 Step dowm 120/208 425 feet

[zodiack]

Hey all

Thanks in advance

I have to re-feed a store and run new conduit over the roof .
I have to run approx 425 feet to re-feed an existing transformer. 277/480 Step down transformer to feed to and 150 amp 120/208 panel all 3 phase
There is and existing transformer and 120/208 panel I have only seen panel

I am running across the roof
My calculations are
2 inch PVC
4 - 1/0 conductors
#2 ground

Do these sizes sound correct

I will re-feed existing transformer
What size step down from 277/480 to feed a 120/208 150 amp panel . 75kva not sure next size down
Not sure the next size down
going to see this morning

 

[ptonsparky]

PVC on a roof will be fun. It will LLS by the end of the first summer and go downhill from there, even if you use all the expansion fittings required. A 2 EG is more than adequate. Ref to table 250.122


A 75 KVA is more than adequate for a 150 amp panel. IMO a 45 could be used depending on the primary and secondary protection of the transformer along with the calculated load. You need to know the transformer size, its existing primary protection etc. first.

 

[kwired]

is your run primary or secondary conductors of the transformer?

Primary should be able to be smaller, like as little as 2 AWG (before factoring any voltage drop), maybe even less depending on calculated load and selected primary overcurrent device, it also should not need a neutral conductor in the supply.

If you are running secondary conductors for 425 feet, you possibly need to increase conductors for voltage drop reasons - knowing calculated load is important here.

 

[zodiack]

I was unable t see the transformer today.
I did see disconnect. It was a 200 fused.
I didn't opened however the load side disconnect was 1-1/2 conduit.
Assuming #1 or #2. Have to wait till Monday.
I do know the existing store panel is 3 phase 150 main breaker.
It was a sub shop now a small bank
I currently will assume 75 Kva
prob fed with smaller wire. The original run
was shorter being underground.
I will see if it is delta to Wye. Save some copper
So at 425 feet 75 kva I only need 150 amps load side 120/208
I might be able to do #1???

 

[zodiack]

Transformer Feed

Transformer Feed

At 425 feet I am going to feed a 75 kva transformer with 1/0. Which at that distance will deliver 150 amp at 480

( Isn't it close to 2-1 meaning I could possibly get 300 amps 120/208 )

My load side is 3 phase 120/208 150 amp main breaker

What size wire can I feed the step down transformer line side... to get 120/208 load side

I am thinking I might be able to go to #2 wire @ 480 line side.

Hey all

Thanks in advance

I have to re-feed a store and run new conduit over the roof .
I have to run approx 425 feet to re-feed an existing transformer. 277/480 Step down transformer to feed to and 150 amp 120/208 panel all 3 phase
There is and existing transformer and 120/208 panel I have only seen panel

I am running across the roof
My calculations are
2 inch PVC
4 - 1/0 conductors
#2 ground

Do these sizes sound correct

I will re-feed existing transformer
What size step down from 277/480 to feed a 120/208 150 amp panel . 75kva not sure next size down
Not sure the next size down
going to see this morning

 

[ptonsparky]

You need to read/study Article 450 and Tables 450.3(A) & (B). Those will tell you the max primary and secondary protection for the transformer.

Use 240.21... to determine the location and size of overcurrent protection of the conductors.

You need to consider both.

 

[Ingenieur]

480 xfmr prim feed
208/480 x 150 = 65 A
use #2 (3.5% vd at 65 A), so oversized due to v drop temp derating should not impact
125 cb (perhaps larger to allow energization of xfmr)

150 120/208 pnl feed
down size fuse to 150
use 1/0 (not sure how long the run is)