The SPST switch, also called a single-pole through switch, comes with one input and one output terminal. Its main function is to make connections and disconnections between input and output.
An SPST switch has features to control a single circuit by making or breaking a connection. So it is a simple switch that is employed for on/off circuits. for its ON position, the current flow and closed path and the OFF position circuit is open with no current flow. In this post, we will discuss the detailed features of the SPST switch and related factors. Let’s get started.
What is an SPST Switch
- SPST full form is single-pole single-throw switch, which has one inner and one outer connection. In other words, this switch is a basic type of switch that controls the current flow circuit.
- Its working is simple, which turns on or off the circuit. In a closed condition, the circuit completes current flows, and when the switch is in an open condition, the circuit breaks the current flow in the circuit.
- Its basic example is the fan switch in your home; when on, the fan is on, and when off, the fan stops.
- This switch is also seen in our home for controlling the connected light and high-voltage power regulated with this switch.
SPST Connections
- spst switch comes with two parts: a common C point and a normally open pin. When the switch is switched on state, from the C common terminal to the normally open pin, current flows.
SPST Switch Structure
- The structure of the switch comes with two metallic plates that make a connection and cause current flow through the completion of the circuit.
- With this connection, the metallic plate is separated to stop the current. In the construction of this switch pole, provide a maximum input connection, and the throw is the output connection of the switch.
- In simple words, with applying one input, we get one output. With this switch we only manage one device or circuit.
- Its connections are made with silver alloy that resists high current. Polyvinyl chloride insulation is used to insulate these contacts.
Circuit Diagram of SPST switch
- Here you can see a diagram of an SPST switch, where switch connections are in a series combination with the light and the battery.
- It allows a single-direction current flow from the battery towards the load. Here you can see the positive pin of the battery connected with the light. The negative terminal of the battery and light are directly connected.
- An SPST switch shows simple working; in a closed condition, the circuit is closed and current flows. As a result, the LED gets on. In open condition, the contacts of the circuit are open, and the light turns off.
- The SPST switch also shows manual working in this combination; we change with on and off conditions and also control the automatic way for controlling different devices.
SPST Switch Working
- The working of an SPST switch is simple, and it is a one-way switch that regulates the circuit’s on and off condition.
- It works through closing or opening a circuit.
- When we press the button, two metallic plates in the switch connect or disconnect according to circuit requirements.
- When plates connect, the circuit is completed, current flows, and the connected load starts working.
- If the plates separated switch is off, it causes a circuit break, so the current does not flow and the load becomes off.
- Its practical example is your home light switch; in the off state, the metallic plates are not connected, and the circuit is open. When the press switch is on, plates connect, causing circuit flow.
- With this circuit connection, we can control current flow, so SPST is used for different devices where one-way control is needed.
SPST Toggle Switch
- An SPST toggle switch is a common switch that controls current flow in different devices. Its structure comes with a handle that moves for controlling connected devices.
- It works based on a handle or lever; when it moves, it opens or closes a switch by making a connection between two points.
- So in this way we control devices easily. The working of the toggle switch is based on the rocker contact system. In simple words, the component that regulates current flow is the rocking connection. When we move the lever, the metallic connection also moves.
- if the connection flip causes pins to break, not current flow. On the other side, a metallic contact connection occurs, current flows, and the load operates.
- An SPST toggle switch comes with a flip cover. that protects the switch from mistaken operation.
- It also avoids the mistaken turning on of the switch and connected devices.
- This feature makes the switch safe to operate and control devices without any hindrance.
- SPST toggle switch used for controlling lights in homes and buildings
Comparing SPST with Rocker, Toggle, and Push Button Switches
| Feature | SPST Switch | Rocker Switch | Toggle Switch | Push Button Switch |
| TYPE | Single Pole Single Throw | Mechanical rocker-type | Lever-type | Momentary or latching push-activated switch |
| Operation | ON/OFF connection | Pressing one side rocks it ON/OFF | Lever flips between ON/OFF positions | Button is pressed to make/break contact |
| Positions | 2 (ON and OFF) | 2 (ON and OFF) | 2 or 3 depending on type | 2 (pressed/unpressed) |
| Action | (stays in position) | (stays ON/OFF) | Maintained (usually) | Momentary or maintained |
| Number of Poles/Throws | 1P1T (1 Pole, 1 Throw) | Can be SPST or SPDT | Can be SPST, SPDT, DPDT | Usually SPST or SPDT |
| Usage | power control | Power switches on appliances | Control circuits, | Doorbells, reset buttons, |
| Design | Simple small switch | Flat rocker that rocks back and forth | Small lever or bat handle | Round/square button |
| Feedback | Clicks or flips ON/OFF | Smooth rocking feel | Distinct lever click | Press and release feedback |
| Example Device | Wall light switch | Power strip switch | Toggle on a control panel | Computer reset or elevator button |
SPST vs SPDT vs DPDT
| Feature | SPST (Single Pole Single Throw) | SPDT (Single Pole Double Throw) | DPDT (Double Pole Double Throw) |
| Full Form | Single Pole Single Throw | Single Pole Double Throw | Double Pole Double Throw |
| Number of Poles | 1 | 1 | 2 |
| Number of Throws | 1 | 2 | 2 |
| Number of Terminals | 2 | 3 | 6 |
| Function | ON or OFF | changes one input between two outputs | Controls two devices each switching between two outputs |
| Equivalent | ON/OFF switch | Changeover switch | Two SPDT switches operated together |
| Example Use | Light switch, power control | Select between two power sources | Motor direction control |
SPST
SPST SWITCH An electrical switch comes with An electrical switch comes with two connections, normally open and common. When the switch operates, the circuit closes, and current flows in the direction from the common terminal to the normally open terminal.
When its terminals are not connected, the circuit is open
SPDT switch
- An SPDT switch is a single-pole, double-throw switch that comes with 3 connections: normally open, normally closed, and common point.
- Input current moves to the switch at the common point and completes the circuit with the NO (normally open) or the NC (normally closed) contacts.
DPDT SWITCH
- A DPDT switch comes with 2 SPDT switches connected internally in the switch design. Common lever operation in the casing of the switch operates both circuits.
- A DPDT switch comes with 6 terminals: two C (common), 2 NO (normally open), and two NC (normally closed).
Read also What is a Single Pole Switch? Features, Types & Uses
Advantages of SPST Switch
- It is a simple circuit that can be connected in a circuit and control current flow.
- Its wiring is easy and helps to make easy connections in circuits with low time.
- It is a simple design and a low-cost option.
- Its working is reliable with using low components without damage.
- It can easily handle current and high voltage values.
- SPST is easy to operate and user-friendly.
- part of homes and industries
Disadvantages
- It provides basic on/off, so limited functionality.
- It is not used for complicated designs where different devices need to be controlled.
- If not used regularly, it causes damage to parts and wear.
- It is affected by dust, humidity, and damage in different conditions.
- High-frequency features cause wear to switch
SPST Switch application
Process control circuits
- This switch is used for a process control system that works for a two-wire sensor. For this circuit, we use 3 SPST connection switches for managing the working of the SPST switch.
- In this way accurate process control occurs in industries.
Power Control
- The main use of this circuit is to on/off the circuit. This switch design is to make or break a connection, thus causing current flow. In the switch-on condition, the circuit is completed, and the current moves to complete the circuit. When the power is off, the circuit stops working.
ON/OFF Applications
- The main use of an SPST switch is to turn on/off a device or circuit. Like our light switch, the fan gets control through on/off operations of the switch.
Part of Electronic Projects
- SPST switches are also employed for electronic projects and for any circuit or project; SPST has control of the power. Like for a small load, the switch performs switching on/off of the circuit without any special wiring process.
Factors to Consider When Selecting an SPST Switch
Read alsoIntroduction to 4 way switch, Wiring, types & Applications
- Different factors are important for selecting an SPST or any type of switch, as explained here.
Size
- Switches have different shapes and sizes, from small sizes like rice to larger switches used in industries for handling devices and tools.A
- small switch used for embedded and portable devices in limited space applications.
- larger switch part of a high-power industrial tool control for durable operations
Default State
The default state is important for automated responses.
- Momentary switches get their default state when the force applied no longer exists.
- Normally Open (NO): circuit open by default, closed in pressed state
- Normally Closed (NC): In this condition, the circuit is by default closed and opens when pressed.
- Maintained switches in new condition until a change occurs manually
Positions
- It shows how many switching components are configured on one element. It is normally considered about throws; position shows actuators in a single switch module. such has four positions A DIP switch has 4 separate actuated switches in a single package.
Mounting types
Switches come with different mounting types for handling mechanical and electrical operations.
- • The lead passes through the board and is soldered on the reverse side.
Surface mount (SMT):
- components connected to PCB pads.
Panel mount:
- It is employed for front panel interfaces and structure.
DIN rail mount:
- It is used for industrial automation conditions.
Pitch
- It is used for through-hole designs, like for breadboard designs.
Actuation
Manual vs. Electronic:
- Switches use force for manual operation or operate electronically.
Tool-activated vs. Glove-compatible:
- uses accurate tools and also works in rugged conditions.
Raised vs. Flat Actuators:
- Raised actuator easily pressed; flat, used for tamper resistance.
Current and Voltage Rating
Voltage rating:
- It is a rating that switches the handle to maximum.
Current rating:
- current that the switch manages without overheating or degrading.
Conclusion
SPST is a simple design switch for different control circuits. Its structure helps to control connected devices easily, from basic light loads to industrial loads. It is low-cost and easy to use, and controls high voltage and current. but it is not used for complex switching. but it is preferred for small projects and devices.
