S&C Instruction Sheet 681-530
61
Thermal Characteristic Protection
One final consideration in the selection of ANSI/US and IEC curve families to achieve
proper power system coordination is the Thermal Characteristic Protection of the Vista
Overcurrent Control. The control will self-protect its internal power supply and current-
sensing circuitry when a pickup setting (in amperes) and/or a time setting exceeds the
thermal limits of the electronic circuitry (in both the electronics module and burden
board assemblies). The control will implement a definite-time response characteristic of
3 seconds at 16 kA for 16-kA units and 3 seconds at 25 kA for 25-kA units. This matches
the performance ratings of the control listed in the “Specifications” section on page 55.
