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The industry standard for appliance manufacturers is to produce an
appliance that when used as designed will operate in a safe manner.
While it is expected that all appliances will fail when they reach their
end of life, it is also expected that the appliance will fail in a safe
manner and will not produce a hazard to the consumer. In the case of
an electrical appliance the safety hazards include the possibility of
shock, electrocution, and fire. For example, when the fan motor in an
electric space heater quits running, the heating elements heat up
sufficiently to cause the high limit thermal cut out to open. When this
happens, the heating elements and the motor are de-energized and
the risk of fire due to an inoperable fan motor is reduced. The space
heater quits working, but it does so in a safe manner.
In the case of the Venmar HRVs several factors must be considered
in the design phase to ensure the appliance will operate in a safe
manner. Since the main moving part in the HRV is the motor, it is
important to understand how motors can fail and how equipment
manufacturers must protect against those failures. My comments in
this regard are applicable to appliances manufactured in the 1990s,
including the Venmar HRV. It would be the responsibility for the
appliance manufacturer to understand all failure modes that may
result in a hazardous condition. The appliance manufacturer would
have to determine how to mitigate the risks of a failure mode given the
type of appliance it is manufacturing.
Motors in electrical equipment can fail in a number of ways. The two
most common occur when the motor rotor becomes locked for some
reason. This can happen due to a physical blockage in the motor or it
can happen at the end of motor life when the motor stops turning. An
appliance manufacturer would be expected to know that the motor is
designed to last a certain number of hours, after which the oil or
lubrication will be consumed, and the motor will stop turning. When
the motor rotor locks, the current drawn by the motor increases and
causes the windings to heat up. This condition results in an
overtemperature condition in the motor. If unchecked, the winding
insulation will degrade causing off-gassing that produces a flammable
vapor. At the same time, the degrading insulation allows for the