Citation

Haslam B, Galler D, Eagar TW. Fire Technol. 2018; 54(4): 967-994.

Copyright

(Copyright © 2018, Holtzbrinck Springer Nature Publishing Group)

DOI

10.1007/s10694-018-0720-4

PMID

unavailable

Abstract

Fractional horsepower motors are used to power exhaust fans such as those found in bathrooms and oven hoods. There was an increase in fires attributed to these motors shortly after the year 2000. Still, many argue that these motors cannot cause fires because they contain a thermal cutoff (TCO) unit that shuts off electrical current when the TCO reaches a specific temperature. In this paper we describe an unsafe failure mode that can occur after extended use. As fans age, the bearings wear out, resulting in heating of the coil wires. Excessive heating results in break down of the wire insulation, which can lead to a short between wires and create an autotransformer configuration. An autotransformer can support high current in only part of the wiring, resulting in resistive heating sufficient for ignition. With the low thermal conductivity of the coil (0.0162

Keywords

Arcing; Ignition; Shaded-pole motor; Thermal protection device; Ventilation fan