Why would someone want to eliminate short-time pickup in CB?

[eemamedo]

I was looking at some manuals online to understand the tripping curve of circuit breakers and noticed that there is a setting option "OFF" when it comes to short-time pickup and short-time delay settings. The "OFF" setting will eliminate both short-time pickup and short-time delay. My question is why would someone wants to put it to OFF mode?

 

[topgone]

I was looking at some manuals online to understand the tripping curve of circuit breakers and noticed that there is a setting option "OFF" when it comes to short-time pickup and short-time delay settings. The "OFF" setting will eliminate both short-time pickup and short-time delay. My question is why would someone wants to put it to OFF mode?

If your application does not involve temporary surge currents, there is no use activating the short-time protection. All you need is the overload (long-time) and the instantaneous trip (fault protection).

 

[eemamedo]

If your application does not involve temporary surge currents, there is no use activating the short-time protection. All you need is the overload (long-time) and the instantaneous trip (fault protection).

I see. Don't you also use this setting during selectivity? I was thinking that you need that setting to carry a fault current for a short period of time, allowing the downstream protection device to trip.
Am I wrong?

 

[Jraef]

I see. Don't you also use this setting during selectivity? I was thinking that you need that setting to carry a fault current for a short period of time, allowing the downstream protection device to trip.
Am I wrong?

No you're not wrong, but what if there is no down stream device?

 

[ATSman]

Selectivity

Selectivity

If your application does not involve temporary surge currents, there is no use activating the short-time protection. All you need is the overload (long-time) and the instantaneous trip (fault protection).

Even if there are surge currents in that time band (xfmer, motor inrush) you always have the option to set the STPU and STTD higher than these normal surges as long as the device can handle such settings.

 

[cuba_pete]

perfect answer. ^^^