Switches and Circuit Protectors
Switch – a device that allows you to “make” or
“break” the connection between two or more
points in a circuit
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Poles and Throws
Pole – the moving contact
Throw – the non-moving contact
Example: Double-Pole, Single-Throw
(DPST)
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Normally Open and Normally Closed
Switches
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Rotary Switches
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Dual-in-line-Package
(DIP) Switches
8 SPST DIP Switch
Circuit Symbol
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Fuses
Fuse – a device that is designed to open
automatically if its current exceeds a
specified value
Actual glass fuse
Circuit Symbol
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Fuse Ratings
Current: the maximum allowable fuse
current before it blows
Voltage: the voltage across an open
fuse that will cause the air in the use to
ionize and allow the open fuse to
conduct.
Fuse ratings are engraved on the metal end caps
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Types of Fuses
High-Speed
Fast-Blow
Instantaneous
Normal Instantaneous
Time Delay
Slow-Blow
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Precautions When Replacing Fuses
Make sure all power is removed from the
circuit
Only replace with a fuse of the same current
rating
Only replace with a fuse of the same or
higher voltage rating
Never replace with a fuse with a higher
current rating
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Micro Fuses
and
Integrated Circuit Protectors
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Circuit Breakers
Circuit Breakers – not destroyed like
fuses when activated
Single – Pole
Double - Pole
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GFI (Ground Fault Interrupt)
GFCI (Ground Fault Circuit Interrupt)
Ground Fault Interrupter (GFI) –
common special-case circuit breaker
RESET Button
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