50 -70 % of the motors are idle most of the time - and whilst they are idle they fail from insulation degradation caused by the aggressive environment and the cracking of the insulation from the thermal stresses of the intermittent start/stop cycles.

The problem - the major cause of motor failures - can only be addressed by monitoring the insulation resistance of idle motors, as conventional motor protection for online problems of energized motors completely ignores idle motors.

Insulation Monitors operate automatically and continuously to give early warning when motor insulation degrades in an idle motor, eliminating the need for costly and inefficient periodic megger testing. In the range of 10 megohms and below the the insulation has lost most of its dielectric strength and the 24 volts that most FailSafe and MotoSafe units use for monitoring gives safe, reliable readings. The diagram below shows the effect of age and aggressive environments on motor insulation levels.

	Monitoring	Range		Alarm	Range
Dielectric Insulation	New motor <<1000MW	Excellent 1000-100MW	Good 100-10MW	Inadequate 10-1MW	Danger >>1MW
		Motor age increasing

The motor's winding is coated with insulation, which resists the leakage of current to the motor frame. Insulation monitors compare the resistance of the insulation to a standard resistance built into the unit determining whether it is greater, equal or smaller then the standard resistance. The unit goes into alarm if insulation resistance is equal or smaller than the standard. Practical experience has shown that an alarm level of not less than 1 megohms gives the best chance of recovering the motor insulation and its dielectric strength by the preventative maintenance measures of drying and revarnishing the insulation but operating the motor after its insulation resistance has fallen to 0.5 megohms reduces the probability of recovery significantly.

Devices use switch gear control voltage to feed the circuitry. Its range varies from 12V DC to 450V AC.

Every unit has built in isolation relay to disconnect the monitor from a energized motor.

Dry type alarm relay contacts provided for operating external or remote alarm devices.

Factory alarm setpoints vary depending on the type of motor, applications and environmental conditions. However custom settings are available.

Built in self-test feature provided in every unit. Units are available with manual or automatic reset.

Monitor may remain connected when motor is meggered.

In the unlikely event of a component failure, the Insulation Monitor Design is such that the normal operation of the motor control is not affected. The enclosure is made of self-extinguishing plastic and all terminals are completely shrouded, for safety DIN rail mounting is standard.