GE SPECTRA RMS Moulded Case Circuit Breakers - Short time.

[NickParker]

Hi,

While checking the use of short time function in this circuit breaker, the manual says the below,

"The inverse-time short-time delay trip characteristic of Spectra RMS circuit breakers provides an increase in protection by providing [highlight #FCE94F]closer tracking[/highlight] of load-operating conditions. The short-time pickup function [highlight #FCE94F]tracks the instantaneous pickup by a factor of 0.5 to 0.8 [/highlight] depending upon specific frame and rating plug."

What is the meaning of tracking here as highlighted?

 

[waross]

Hi Nick. Can you provide a link to the breaker info?
A look at the tripping curve may help.
I am guessing that it means the ratio between the short-time pickup and the instantaneous pickup.
I am used to seeing an adjustable ratio of long-time pickup (breaker rated current) to instantaneous pickup of 0.1 to 0.2
With a long-time pickup ratio of 0.5 to 0.8 you will never get a motor started DOL.
A look at the trip curve may help explain the term.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[NickParker]

Hi Waross,

The TCC is attached.

 

[waross]

I am as puzzled as you Nick.
It may be that the short time trip is adjustable as well as the instantaneous trip, but that is a guess.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

Looks like one adjustment that changes both the instantaneous and short time portions of the characteristic. As you raise the instantaneous the short time also raises, tracking the instantaneous.

 

[dpc]

Yes David is correct, the short time settings move with the instantaneous pickup setting. The short time has a fixed I2t function. Out of curiosity I plotted the curve in EasyPower and adjusted the settings and it seems to be doing it correctly although there is a terminology issue.