OCPS/Feeder/Load Calc

horsegoer

Senior Member
Location
NJ
1200A CB feeding 800A panel with 2 sets 4 #600. Wire size makes sense for the 800A panel but the breaker being 1200A is ok??
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Doesn't sound okay. Maybe the breaker has an 800A trip setting? Or you are leaving out important details, like the panel has a main breaker? Otherwise not okay.
 

horsegoer

Senior Member
Location
NJ
Didn't want to start another thread but here's another. Seems to be a lot of mistakes by engineer.

show 250A frame breaker with 400A "rating" I guess. The actual breaker "rating" can''t be larger than the frame size can it?

Also this is feeding a 260A ATS with 4# 250 mcm which is only good for 255A.

I's think you need bigger breaker and feeder( maybe #300).?
 

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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Didn't want to start another thread but here's another. Seems to be a lot of mistakes by engineer.

show 250A frame breaker with 400A "rating" I guess. The actual breaker "rating" can''t be larger than the frame size can it?

Also this is feeding a 260A ATS with 4# 250 mcm which is only good for 255A.

I's think you need bigger breaker and feeder( maybe #300).?
I think 250AF is the plug rating and 400A is the frame size. probably just a typo. AF should maybe be AT.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I think 250AF is the plug rating and 400A is the frame size. probably just a typo. AF should maybe be AT.
Agree..
+ 250 amp is the best choice providing it satisfies the load. With a conductor ampacity of 255, a 250 amp plug is a safe install.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Short answer "yes".
"Rating plug", I fear, shows my age :)
For many years, before electronic trip, larger breakers had interchangeable rating plugs to set the current rating.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Short answer "yes".
"Rating plug", I fear, shows my age :)
For many years, before electronic trip, larger breakers had interchangeable rating plugs to set the current rating.
It's still used in some breakers.
images

In this one, the "rating plug" is the small box on the lower right with the white label.
Looks like this up close;
SRPE100A70_1.jpg

So you bought a breaker in a "Frame" size, like in this case a 125AF, and by installing a 70A "rating plug" you made it a 70A amp trip (70AT) breaker. The issue is/was that UL did not like the idea of adjustable trip circuit breakers because of the potential inaccuracy of the dial setting and/or the likelihood of Joe Bubba maintenance guy doing a "crank 'er up" on it when it trips rather than find out why. The rating plug was pre-calibrated and made it a more deliberate and traceable act to change it (in theory).
 

topgone

Senior Member
It's still used in some breakers.
images

In this one, the "rating plug" is the small box on the lower right with the white label.
Looks like this up close;
SRPE100A70_1.jpg

So you bought a breaker in a "Frame" size, like in this case a 125AF, and by installing a 70A "rating plug" you made it a 70A amp trip (70AT) breaker. The issue is/was that UL did not like the idea of adjustable trip circuit breakers because of the potential inaccuracy of the dial setting and/or the likelihood of Joe Bubba maintenance guy doing a "crank 'er up" on it when it trips rather than find out why. The rating plug was pre-calibrated and made it a more deliberate and traceable act to change it (in theory).
Lazy electricians always do those: if a breaker trips, rather than running thru the wiring path, they just crank the adjustable trip setting up! Easy-peasy as the Brits say!
 
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