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terminals and leads, heating or cooling effect of the terminals and external leads, rate of

temperature rise, air flow, shock, vibration and other environmental and operating conditions

unique to the application.

The product and application being tested will determine the number of cycles that must be run to

determine the maximum “normal” operating temperature. “Overshoot” temperatures should be

included in the determination of the maximum “normal” operating temperature. The overshoot

temperature is often considerably higher than the temperature reached at the moment the

thermostat opens. The conclusion of these tests will provide the maximum “normal” operating

temperature at the thermal cutoff (at maximum anticipated voltage, ambient temperature, etc).

The overshoot temperature seen by the thermal cutoff after the thermal cutoff opens in the

application must also be carefully examined.

Manufacturing tolerances and variations should be carefully considered, and a sufficient number

of units evaluated, to provide a statistical basis on which to determine the operating overshoot

temperatures.

After obtaining the above information, test the product under fault conditions and monitor to

determine that desired fault condition temperatures are not exceeded.

Where there are a variety of fault conditions, (e.g., short-circuited thermostats and transformer

secondaries, locked motor rotors and solenoids, high ambient temperatures, restricted or

blocked airflow, etc.), consideration should be given to multiple fault conditions which could

occur simultaneously during the lifetime of the product, and to faults which may cause localized

overheating in areas away from the TCO.

When the fault conditions have been set up, note the temperature of the dummy cutoff when the

maximum desired temperature limit is reached. At this point the circuit is manually interrupted.

This test should be run several times, in several different units. In some applications, it will not be

possible to “save” the tested item from damage, but only prevent the product from creating an

external fire or electrical hazard. Damaged products should not be retested, since the results may

not be the same as with undamaged units. The MICROTEMP

should be equal to or less than the temperature recorded at the dummy thermal cutoffs at the

time the maximum desired temperature is reached.

CAUTION . . . Excessive overshoot temperatures after the opening of the thermal cutoff may cause

dielectric breakdown of the thermal cutoff and allow reconduction to occur. Functional thermal

cutoffs should be tested to verify proper operation of the thermal cutoffs in the application (see

figure 3).