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General switch information that may be helpful in understanding how switches work and selecting the right switch for the job.
Some terminology when hunting for the right type of switch or coming across a switch in a package, you can tell exactly what it does without opening & trying it out when reading the information below about switches. Some manufacturers of switches have indicator lamps that are operated in different configurations such as independent (not connected to the controlling circuit) or dependent (connected to the circuit and always the same voltage). I only describe the non-lighted versions to help you better understand the configurations. Scroll down to understand some characteristics of some switches that are out there and what you'd need to be aware of.
SPST = Single pole, single throw. This is a most basic switch. The single pole can be consisted as a "single current".
SPDT = Single pole, double throw. Double throw can be consisted as "two different paths" for the current to follow.
DPDT - Double pole, double throw. In other ways, two SPDT switches joined together but with one lever activating both at the same time.
There are other variants such as 3PST (3 Pole, single throw), 4PDT (4 Pole, double throw), and so forth to describe the basics.
Switch types -
Self explanatory with different styles available, duck bill, paddle, rocker, etc. The mounting hole are usually round or rectangular. some are even square. There are rocker switches that can be mounted in round holes for ease of installation. Switches with round holes almost always have a long notch on the body of the switch which indicates the "down" position of the switch.
Switch positions -
Other things to know besides the above is these symbols which describes the method of operation of the switches and the positions offered. There are two types of SPST switches, momentary and on. To determine what type it is, look for the parenthesis "( )" to indicate momentary.
Here are a few examples...
SPDT on-on = This is a single pole, double throw switch with only two positions. No center off here.
SPDT (on)-off-on = This is a three position switch which has a center position that is off, one side is momentary which when released, it moves back to off. The other side will hold the position when released.
SPDT off-on1-on2 = Again, a three position switch but with a twist. The off position is not in the middle! In the middle position (or on1), only one side of the switch is on. With the switch in the on2 position, both circuits are activated. This is known as a "progressive switch"
Lighted switches - This gets a little more dicey to understand.
Some are dependent, which means they require connection to the circuit. Most lighted 12vdc switches are of that type where only one extra terminal is provided to serve as a ground for the lamp. While it's possible to use the switch as a ground switch (as opposed to positive) by connecting the extra terminal to positive but this only works for incandescent indicator lamps which are not polarity sensitive. If it's a LED type of lamp, it's polarity sensitive and you cannot reverse the current while expecting the lamp to work. Switches with neon indicator lamps or 120vac bulbs are designed for household circuits. Keep in mind that these lighted switches are limited to the ratings of the lamp. While it's possible to wire a neon switch in an automotive application, just don't expect the lamp to work.
Some are independent, which means the lamps don't care what circuit it's controlling. This offers more flexibility. The switch body can handle any type of rated voltage and the lamp can be wired independently.
Some have dual indicators, which means they are usually wired in such a way that one serves as an illumination lamp while the other serves as a "status" lamp.
There are more configurations that are only limited to the imagination on how they can be wired. I've wired dual indicator lamps that flash simultaneously when it is in the on position much like the TM-4's to get the idea. Do pay attention to the package what you are getting.
Switch ratings -
A switch rated 125vac, 3a - 250vac 1a doesn't mean it's only for high voltage applications. It's just shows the maximum capacity. Switches with these rating levels can handle up to 20 amps on a 12vdc system.
Hope you'll get some idea of how a switch works just by looking at the package.
Some terminology when hunting for the right type of switch or coming across a switch in a package, you can tell exactly what it does without opening & trying it out when reading the information below about switches. Some manufacturers of switches have indicator lamps that are operated in different configurations such as independent (not connected to the controlling circuit) or dependent (connected to the circuit and always the same voltage). I only describe the non-lighted versions to help you better understand the configurations. Scroll down to understand some characteristics of some switches that are out there and what you'd need to be aware of.
SPST = Single pole, single throw. This is a most basic switch. The single pole can be consisted as a "single current".
SPDT = Single pole, double throw. Double throw can be consisted as "two different paths" for the current to follow.
DPDT - Double pole, double throw. In other ways, two SPDT switches joined together but with one lever activating both at the same time.
There are other variants such as 3PST (3 Pole, single throw), 4PDT (4 Pole, double throw), and so forth to describe the basics.
Switch types -
Self explanatory with different styles available, duck bill, paddle, rocker, etc. The mounting hole are usually round or rectangular. some are even square. There are rocker switches that can be mounted in round holes for ease of installation. Switches with round holes almost always have a long notch on the body of the switch which indicates the "down" position of the switch.
Switch positions -
Other things to know besides the above is these symbols which describes the method of operation of the switches and the positions offered. There are two types of SPST switches, momentary and on. To determine what type it is, look for the parenthesis "( )" to indicate momentary.
Here are a few examples...
SPDT on-on = This is a single pole, double throw switch with only two positions. No center off here.
SPDT (on)-off-on = This is a three position switch which has a center position that is off, one side is momentary which when released, it moves back to off. The other side will hold the position when released.
SPDT off-on1-on2 = Again, a three position switch but with a twist. The off position is not in the middle! In the middle position (or on1), only one side of the switch is on. With the switch in the on2 position, both circuits are activated. This is known as a "progressive switch"
Lighted switches - This gets a little more dicey to understand.
Some are dependent, which means they require connection to the circuit. Most lighted 12vdc switches are of that type where only one extra terminal is provided to serve as a ground for the lamp. While it's possible to use the switch as a ground switch (as opposed to positive) by connecting the extra terminal to positive but this only works for incandescent indicator lamps which are not polarity sensitive. If it's a LED type of lamp, it's polarity sensitive and you cannot reverse the current while expecting the lamp to work. Switches with neon indicator lamps or 120vac bulbs are designed for household circuits. Keep in mind that these lighted switches are limited to the ratings of the lamp. While it's possible to wire a neon switch in an automotive application, just don't expect the lamp to work.
Some are independent, which means the lamps don't care what circuit it's controlling. This offers more flexibility. The switch body can handle any type of rated voltage and the lamp can be wired independently.
Some have dual indicators, which means they are usually wired in such a way that one serves as an illumination lamp while the other serves as a "status" lamp.
There are more configurations that are only limited to the imagination on how they can be wired. I've wired dual indicator lamps that flash simultaneously when it is in the on position much like the TM-4's to get the idea. Do pay attention to the package what you are getting.
Switch ratings -
A switch rated 125vac, 3a - 250vac 1a doesn't mean it's only for high voltage applications. It's just shows the maximum capacity. Switches with these rating levels can handle up to 20 amps on a 12vdc system.
Hope you'll get some idea of how a switch works just by looking at the package.