Cold Load Pickup

When a typical load has been without supply for a period of time (hours) it loses its diversity.

When power is restored the load is initially higher than usual because many or all of the thermostat controlled devices such as heaters, refrigeration, air conditioners etc. will turn on.

The longer the period without supply the greater the loss of diversity and the higher the load current will be when supply is restored.

If the supply is off long enough the load will eventually lose diversity altogether and any further extension of the outage will not cause the initial load current when supply is restored to increase any further.

The increase in load current after a prolonged outage could cause overcurrent protection to operate unnecessarily.

The purpose of the Cold Load Pickup (CLP) feature is to automatically compensate for the loss of diversity by adjusting the overcurrent pickup thresholds until the load regains its diversity and steady state load conditions return.

It works by measuring the time that supply was lost and then temporarily raising the Setting Current for the selected elements according to the time the load has been without supply.