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Electric motor rewinds have been at the heart of our
business for 45 years, so there isn't much we don't know about the reasons for
motor failure. Here we look at why heat causes motors to stop working.
We’ve been rewinding and repairing electric motors for 45
years, so there isn’t much we haven’t seen when it comes to the causes of motor
failure. Heat, from a variety of sources, is among the most common reasons for
an electric motor to stop working. Here we discover why and how this happens.
Why does heat cause motor failure?
Before we look at the primary reasons for motors being
exposed to potentially damaging temperatures, we should ask why overheating
leads to failure. It’s actually very straightforward:
The windings within a motor are coated with a special
insulating varnish or lacquer
When the coil becomes too hot, the insulation melts
This causes the windings to short circuit and therefore the
motor to stop operating.
Each time a motor’s windings rise 10°C above the design
operating temperature, the life of the insulation is halved – even during a
short period of overheating.
Now we’ll look at the three main reasons for motors being
exposed to excess heat:
Unsuitable for application
If a motor is too small for the application it’s being used
for, or if it has the wrong starting current (also known as inrush current) and
torque characteristics, it will operate hotter than its rated temperature. It’s
vital that a motor is matched to its connected load, whether that’s a pump,
HVAC system or humidifier.
When a motor is operated in an environment with a high
ambient temperature, heat cannot be conducted from it as quickly as its design
allows for. Therefore a motor located in a poorly-ventilated area or near a
heat source could be exposed to temperatures high enough to cause damage.
Ambient temperature shouldn’t be the only consideration – a
motor with plugged air passages or blocked cooling fans and vanes will quickly
If a motor is enclosed - in a protective housing, for
instance – then the ambient temperature is limited to that space only and may
exceed the rated level. Temperatures in enclosed areas should be monitored and
if they are excessive then ventilation added.
If you’d like to know more about our electric motor rewinds
and repair service, give us a call on 01621 868138 or email