Low Voltage CB Short time pick up tolerance..?

[Isaiah]

Hi Guys,

So recently I came into a dilemma, there was testing being done on a low voltage cb with a micrologic 6.0P LSI the breaker's frame and trip rating is 800A the short time pick-up was set at 1.5 (min). so in that sense the pick up should be 1,200A. Now once I was doing revision on the data sheets i noticed test results as low as 840A-1000A for the short time pick up! it just feels wrong but when asked for a source i couldnt find any sources or tolerances stating that the short time pick up test results should be within a certain tolerance like IT has our NETA tables. Any help please in knowing if there is a such thing as a tolerance threshold for short time pickup? thanks sorry for the long explanation

[Kalbi_Rob]

Hi Guys,

So recently I came into a dilemma, there was testing being done on a low voltage cb with a micrologic 6.0P LSI the breaker's frame and trip rating is 800A the short time pick-up was set at 1.5 (min). so in that sense the pick up should be 1,200A. Now once I was doing revision on the data sheets i noticed test results as low as 840A-1000A for the short time pick up! it just feels wrong but when asked for a source i couldnt find any sources or tolerances stating that the short time pick up test results should be within a certain tolerance like IT has our NETA tables. Any help please in knowing if there is a such thing as a tolerance threshold for short time pickup? thanks sorry for the long explanation

Dependent on Manufacturer specifications. Long time Pickup typically have 10% deviation, and Short time pickup is a multiple of that pickup, so it should also fall with in the same deviation specs. That being said, you also have to take into effect your own test set deviation error %. An 800A breaker should not be tripping before 1100A on a 1.5x setting. I would definitely re-verify your LT pickup and slow ramp the trip for ST pu.

"Short-time delay and pickup. The short-time delay characteristic provides protection against short-circuit or fault conditions. An intentional delay is provided for coordination or selectivity with other protection devices. The short-time pickup is a multiple of the long-time pickup. "
-NETAworldjournal.org https://netaworldjournal.org/primary-injection-testing-on-low-voltage-circuit-breakers/

[Jcrouch]

Hi Guys,

So recently I came into a dilemma, there was testing being done on a low voltage cb with a micrologic 6.0P LSI the breaker's frame and trip rating is 800A the short time pick-up was set at 1.5 (min). so in that sense the pick up should be 1,200A. Now once I was doing revision on the data sheets i noticed test results as low as 840A-1000A for the short time pick up! it just feels wrong but when asked for a source i couldnt find any sources or tolerances stating that the short time pick up test results should be within a certain tolerance like IT has our NETA tables. Any help please in knowing if there is a such thing as a tolerance threshold for short time pickup? thanks sorry for the long explanation

Since it is a Micrologic 6.0 (Ground Fault Equipped) were you using a secondary injection test set to defeat GF? My guess would be either the breaker picked up too low, you still had GF active, or you didn't have the thermal memory inhibited. If With that being said the STPU Threshold for a Micrologic 6.0(A/P/ETC.) is +/- 10%. A Micrologic 6.0 is a LSIG Breaker.