Vacation Break for Electrical Machines

Are you overloaded? Have you become a part of the highly stressed
modern working environment? You may need a break - a vacation, a
change in environment, a change of pace...

Similarly, machines can be overloaded too. Those that were
designed for a particular system are often pushed to their limits
when new requirements emerge.

Just like the final straw that breaks the camel's back, electrical
machines too, can reach their breaking point. If there is no
vacation for them, they will burn.

Fuses and circuit breakers are designed to stop the current in a
circuit before any damage can occur - create a vacation or a break
for them.

A circuit breaker is one of the ways to prevent motors (or other
electrical machines) from burning due to overloading. All
electrical motors produce heat when running. At the time of a
fault, this heat builds up at a much higher rate than it can be
dissipated. This can result in damaged equipment, fire or even

The electrical protective device like the circuit breaker is
designed to de-energize the circuit before this heat level becomes

There are basically 2 means of activating a break - thermally
(heat) or magnetically.

Thermal circuit breakers make use of bimetallic strips that will
bend due to the different expansion rates of each of the metals in
the strip. The bending of the strip will move a tripping mechanism
latch that will then open up the contacts of the circuit breaker.

Because bimetallic strips take time to heat up and bend, this type
of tripping device is used for tripping prolonged overloaded
situations. The setting for breaking the circuit at a particular
overload value can be adjusted.

Magnetic circuit breakers make use of the field strength of
magnetic coils to trip a latch that will then open up the contacts
of the circuit breaker. This method is used for high current
faults, like in a short circuit. This method is designed to trip

A thermal-magnetic circuit breaker incorporates both a thermal
strip and a magnetic coil. This type of circuit breaker is able to
protect against momentary overloads as well as high or short circuit
current faults.

What happens if the circuit breaker is placed in a high temperature
environment? The thermal bimetallic strip bends on high temperature.
In this case, the current is not causing the high temperature in the
bimetallic strip, but the ambient air is! The current may still be
below the safe operating rated value for the motor.

In this case, a compensating bimetallic strip may be incorporated
into the circuit breaker to eliminate this type of error. These
circuit breakers are often used in hot areas like furnace, oven, and
boiler rooms.

Circuit breakers can be reset very quickly, once they have tripped.
Can your break or vacation be reset very quickly too? Don't reset.
Take a long break!

Until next time...

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Thomas Yoon