150

Figure 14

Dimensions are shown in inches (millimeters).

Thermal Gradients

Ideal TCO placement subjects the entire TCO case, leads, epoxy seal and internal components to a

uniform temperature environment.

Care should be exercised in the placement of the TCO to minimize thermal gradients across the

TCO body. In certain applications, the TCO can be mounted in a position where heat is conducted

to the body of the TCO through one of the leads, resulting in thermal gradients across the TCO.

Over time, the TCO life can be reduced by thermal gradients if the isolated (epoxy) lead is at a

consistently lower temperature than the case lead. Long term testing is recommended in

determining whether these conditions exist in the application.

To minimize the effects of thermal gradients and the temperature increase of the TCO body from

this heat flow, attach the isolated (epoxy) lead, rather than the case lead, to the heat source.

TCO dummies can be supplied with thermocouples on both ends to facilitate gradient evaluations.

Temperature Limits

The temperatures experienced during normal operation, including expected temperature overshoots,

will determine the life expectancy of the TCO. Nuisance trips can result if the thermal cutoff rating

is too close to the temperatures experienced during normal operation. Thermal cutoffs of any

temperature rating should not be subjected to continuous normal temperatures in excess of

200°C. Additionally, overshoot temperatures after the opening of the thermal cutoff should be

minimized to avoid dielectric breakdown and reconduction of the thermal cutoff.

.09 MIN.

(2.3 mm)

.04 MIN. RAD.

(1.0 mm)

.70 MIN. (17.8 mm)