Automatic Reset

These overload relays are field convertible from hand reset to automatic reset and vice-versa. On automatic reset, after tripping, the contacts automatically reclose when the overload relay has cooled down. This is an advantage when the overload relays are inaccessible.

However, automatic reset of overload relays should not normally be used with two-wire control. With this arrangement, after an overload relay trip, the motor restarts when the overload relay contacts reclose. This can result in the possibility of danger to personnel. The unexpected restarting of a machine can cause the operator or maintenance personnel to be in a hazardous situation while attempting to find out why the machine has stopped.

In addition, if the cause of the overload has not been resolved, when the motor restarts, the overload relay will trip again. This cycle will repeat, and eventually the motor will burn out due to the accumulated heat from the repeated inrush and overload current.