BULLETIN FROM....

Spring 1996

A L E RT

"ROOF­TOP HEAT/COOL UNITS"

A roof­top heat/cool unit at a Manitoba school recently suffered damage from overheating of the low voltage blower motor, wiring and transformer.

The unit in question is fed 600 v. power with a step-down transformer within the unit supplying 230 v. to the blower motor.

It appears the Thermal overload" protection on the 230 v. blower motor did not operate when the motor overheated allowing the overheating of the 230 v. wiring and the step­down transformer. The low voltage components were burnt beyond repair.

We understand the unit is CSA and CGA approved at the factory, however, when the motor thermal overload did not operate, the safety devices on the 600 v. side did not trip and the damage occurred.

Were it not for the fact that school personnel detected the odour of smoke and extinguished the fire, further damage and a serious fire loss could have occurred.

Although the situation as described above may be rare, if you have similar units at your school, consideration should be given to installing additional protection such as a fusible disconnect switch on the 230 v. power supply or replacing the 230 v. blower motor with a 600 v. motor making the 230 v. supply redundant. Any change should be approved by Manitoba Hydro a/o Manitoba Department of Labour.

If any unit gives any indication of problems (e.g., tripping of the motor overload which requires resetting), the situation should be monitored, logged and maintenance supervisors should be notified.

AWARENESS AND COMMUNICATION CAN PREVENT LOSSES

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