Specifications

9 8 % F i l l R a t e a n d i n c R e a s e d P R o F i t a b i l i t y – G u a R a n t e e d
Switches
Switches
83
Selecting a Switch
There are three important features to consider when
selecting a switch:
1. Contacts - e.g. single pole, double throw.
2. Ratings - maximum voltage and current.
3. Method of Operation - toggle, slide, key, etc.
Glossary of Terms for Switch Contacts
S.P.S.T. - Single Pole, Single Throw.
S.P.D.T. - Single Pole, Double Throw.
D.P.S.T. - Double Pole, Single Throw.
D.P.D.T. - Double Pole, Double Throw.
Pole - number of switch contact sets.
Throw - number of conducting positions, single or double.
Way - number of conducting positions, three or more.
Momentary - switch returns to its normal position when released.
Open - off position, contacts not conducting.
Closed - on position, contacts conducting, there may be
several on positions.
For example: the simplest on-off switch has one set of contacts
(single pole) and one switching position which conducts (single
throw). The switch mechanism has two positions: open (off) and
closed (on), but it is called ‘single throw’ because only one
position conducts.
Switch Contact Ratings
Switch contacts are rated with a maximum voltage and current,
and there may be different ratings for AC and DC. The AC
values are higher because the current falls to zero many times
each second and an arc is less likely to form across the
switch contacts.
This information is courtesy of www.ElectronicsClub.com.
S.P.S.T. On/Off
Has two positions:
Closed (on) and open (off).
Only closed (on) position
can power the load.
S.P.D.T. On/On
Only one of the loads can be
powered at a time.
Moves from one contact to the
other without a center position.
S.P.D.T. On/Off/On
Only one of the loads can be
powered at a time.
Has off as the center position.
D.P.S.T. On/Off
Both load terminals can be
powered at the same time.
They are independent of
each other and could be of
different voltages.
D.P.D.T. On/On
Functions like two separate
S.P.D.T. switches operated by
the same actuator. Two loads
can be powered at a time.
Moves from one contact to the
other without a center position.
D.P.D.T. On/Off/On
Functions like two separate
S.P.D.T. switches operated by the
same actuator. Two loads can be
powered at a time.
Has off as the center position.
Switch Specifications