Feeder Calc

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Alwayslearningelec

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Have a 400a temp panel277/280v feeding (3) loads
  1. 100A disconnect switch
  2. 100A panel
  3. 2000A ats with the note below.
Not possible to feed 2000A ATS from a 400A panel obviously unless I'm missing something, correct?

PROVIDE TEMPORARY TAP FEEDER FOR
CONNECTION OF TEMPORARY PANEL
WITH TWO SETS OF 4#3/0+1#1/0 IN 3"C.
TEMPORARY TAP FEEDER LENGTH TO BE
LESS THAN 10 FEET. COORDINATE POWER
OUTAGE FOR TEMPORARY TAP FEEDER
INSTALLATION.
 
Sounds like the tap for the temp panel is connected to the ATS not the other way around. Need more info but the EGC might be to small.
 
As long as your load doesn't exceed 400 amps then the 400 amp panel can feed a 2000 amp ats. I assume this is temp so ....
 
horsegoer said:
2000A ats the load would have to be over 400A?
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You know that is not true... the load is what is on the ats. It can be 5 amps for all we know. A 400 amp panel is temporarily feeding a 2000 amp ats. If this is during construction then the load can be anything. I assume less than 400 amps or they would have designed it differently.
 
Dennis Alwon said:
That makes sense but why 2 sets of 3/0. That feeds the 400 amps.

I don't see any note for an ATS.
Click to expand...
That key RD12 refers to the note I posted above.
So essentially right now the ATS normal feed is coming from a line side tap of the main switchboard. The main switchboard needs to be shut down so they want to temp out the normal side of the ATS since the exiting normal side feeder will be de-energized. So they are bringing a temp feeder from a 400A panel to the normal side of the 2000A ATS temporarily.
 

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horsegoer said:
That key RD12 refers to the note I posted above.
So essentially right now the ATS normal feed is coming from a line side tap of the main switchboard. The main switchboard needs to be shut down so they want to temp out the normal side of the ATS since the exiting normal side feeder will be de-energized. So they are bringing a temp feeder from a 400A panel to the normal side of the 2000A ATS temporarily.
Click to expand...
That makes sense the load on the ATS is probably very small.
 
horsegoer said:
Well it's and FIRE PUMP ATS so the load is the fire pump. Not sure of the power req. for the fire pump but if small as you say why a 2000A ATS?
Click to expand...
No idea why the engineer downsized the temp feeder. What size circuit breaker is in the 400 amp panel for the ATS feeder?
 
horsegoer said:
The ATS is being fed from the temp panel, for sure
Click to expand...
Since the temp panel is 400 amps that would be the maximum current that would connected to the normal side of the ATS. It could even be less if there is a smaller OCPD ahead of the feeder in the 400 amp panel.
 
Following IEEE 242/2001 page 312 [chapter 9.5.2.3 Intermediate and long-time zones] and considering the 3" conduit as large size cable in air #3/0 copper conductor XLPE insulation may withstand 1100 A for 3.5 minutes [3 time in a year] .
 
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