Reallly long panel feeder -- how to connect to panel and feeder breaker?
Reallly long panel feeder -- how to connect to panel and feeder breaker?
(OP)
Hi Fellows,
I'm working a project involving great distances from a main switchboard or power panel to some 250A 480/3 panels. The champion is an 850-foot run. In order to keep voltage drop to less than 3 percent, I calculated the need for 4 sets of 350 MCM per phase at an 80 percent load on the panel (200A) for this longest run.
My question is, I haven't found a 250A panel that can accept 4 x 350 MCM per phase at the main lugs, nor a switchboard breaker that can do so either. Do we need to spot a wiring box at each end to reduce the feeder size to "normal" (1 x 250 MCM) at each end?
Sorry for the elementary question -- I've just never run into these distances before. I've always been able to space my mains as needed to reduce feeder distances, but not in this cavernous building...
Thanks for your help!
I'm working a project involving great distances from a main switchboard or power panel to some 250A 480/3 panels. The champion is an 850-foot run. In order to keep voltage drop to less than 3 percent, I calculated the need for 4 sets of 350 MCM per phase at an 80 percent load on the panel (200A) for this longest run.
My question is, I haven't found a 250A panel that can accept 4 x 350 MCM per phase at the main lugs, nor a switchboard breaker that can do so either. Do we need to spot a wiring box at each end to reduce the feeder size to "normal" (1 x 250 MCM) at each end?
Sorry for the elementary question -- I've just never run into these distances before. I've always been able to space my mains as needed to reduce feeder distances, but not in this cavernous building...
Thanks for your help!
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies






RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
Link
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
That's what I was thinking too...
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
What you are looking for is essentially a link box. But between two sets of armoured cable. Try asking a generating set packager or a panel maker, they will have them, so you don't have to re-invent the wheel.
Sorry for the long explanation.
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
-JFPE
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
I'll have a few options now for my client. Eng-tips rules!
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
In my experience buck, boost most often implies auto-transformers.
In your case, you will probably be looking at about 4160 Volts.
An auto transformer is NOT recommended.
An open circuit on the 480 Volt winding on the receiving end will put 4160 Volts where you are expecting 480 Volts.
Also, the advantage of an auto-transformer over a two winding transformer is slight with a step up ratio of 4160:480, or 8.66:1 Auto-transformer boost is most economical with small ratios like 1:4 (eg: 120V + 480V = 600V)
The higher the step up ratio the less size advantage to an auto-transformer and the more danger in the event of an open circuit secondary winding.
I love auto-transformer applications, but there is a limit.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Reallly long panel feeder -- how to connect to panel and feeder breaker?