How to Wire Double Pole, Double Throw Switch? Wiring DPDT

Electrical Technology

How to Wire an DPDT Switch? Controlling 120V/240V & 230V Circuit using Double Pole, Double Throw Switches

Table of Contents

What is Double Pole, Double Throw (DPDT) Switch?

DPDT stands for Double Pole, Double Throw switch. It is basically two SPDT switches packed in a single unit and operated by a single lever (common for both single pole, double throw switches). In short, DPDT (Double Pole, Double Throw) switch is used to control two separate circuit connected to two inputs supply.

Double Pole, Double Throw switch has 6 terminals as L1, L2, A1, A2, B1 and B2. The L1 and L2 terminals are connected (not always the case) to the incoming lines (say Hot 1 and Hot 2 in case of 240V – NEC or Phase and Neutral in case of 120V or 230V – IEC) and A1, A1, B1 and B2 are connected to the load points according to the design.

Double Pole, Double Throw (DPDT) switch is used to control two separate appliances connected to the supply for example, a water heater can be toggled between 120V and 240V supply using DPDT switch (wiring diagram is given below), where both supply lines (Hot1 and Hot2 or Line and Neutral) must be switched ON or OFF at the same time for single operation as the action is interchangeable due to the DPDT switch.

Caution: Switches are always wired on the Phase (Line or Hot) wires same as fuses.

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Construction & Working of DPDT Switch?

The following gif and short video illustrates how a double pole, double throw switch works in the circuit.

Short Video:

Let’s see how to wire a DPDT switch for different applications.

Controlling & Wiring Two Light Bulbs using DPDT Switch

The following basic wiring diagram shows two colored (Blue and Red) LED bulbs are wired and controlled through a DPDT switch. As shown, the two wires supply (battery or AC source) are connected to the input terminals of double pole, double throw switch terminals (L1 and L2).

The Blue LED bulb is connected through A1 and A2 while the Red color LED light is wired to B1 and B2. At position one (say Up), the Blue light bulb is glowing as the circuit is completed via A1 and A2 and the Red bulb is OFF. At position two (down), the Red light bulb is glowing as the circuit is completed via B1 and B2 and the Red bulb is OFF.

The following gif shows the operation of the above circuit.

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Controlling the Direction of Motor Rotation using DPDT Switch

As shown in the following wiring diagram, the rotation of motor direction is controlled through double pole, double throw switch via phase reversal method.

The two wires supply (as phase, line and neutral) is directly connected to the L1 and L2 terminals of the DPDT switch. The motor is wired to the load terminals of the switch where A1 is connected to B2 and A2 is connected to the B1.

When the switch handle is UP, the motor is rotating in clockwise direction as the circuit is completed through A1 and B2. When the switch lever is down, the motor runs in anticlockwise direction as the circuit is completed through A2 and B1.This way, the rotation of motor direction can be easily changed using DPDT switches.

The following gif shows the operation of the above circuit.

How to Toggle Water Heater between 120V & 240V using DPDT Switch?

A water heater can be toggled between 240V and 120V supply using a double pole, double throw switch. To do this, connect a Hot 1 (black color) from the 2-poles, 30 amp circuit breaker to the water heater element. Now connect Hot 1 (red color) from the breaker to the A2 terminal of the switch and again, connect the L2 terminal to the water heater terminal box.

Click image to enlarge

Now, connect a neutral from the busbar to the B2 terminal of the switch. Finally, connect the ground wire to the water heater. The L1, A1 and B1 terminals screws are unused in this case.

When the switch position is Up, the water heater operates on 240V via Hot 1 and Hot 2. When the switch position is down, the water heater runs on 120V supply via Hot 1 and Neutral.

Keep in mind that you can control any of the two electrical appliances using double pole, double throw switch where one circuit can be operated at the same time while the second one will be OFF.

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Toggle Water Heater between 120V & 240V using DPDT Center-OFF Switch

The above wiring diagram only switches the supply between 240V and 120V, to add an additional feature to the circuit e.g. “supply off”, we will use DPDT switch with center-off position. In this case, we will need two breakers viz 30A, 2-Poles, 240V for hot1 and hot 2 and 20A, single pole, 120V for neutral and hot wires.

Just wire the double pole, double throw switch to the water heater as shown in fig below.

Click image to enlarge

The circuit will work as follows.

Switch lever at Up Position = Water heater operates on 120V supply as the circuit is completed through Line and Neutral (via B₁, L₁ and B₂, L₂ terminals).
Switch handle at Center Position = Switch OFF – No supply to the water heater.
Switch lever at Down Position = Water heater runs on 240V supply. The circuit is completed through Hot1 and Hot2 (via L₁ and L₂ are connected (through A_1, , A₂ and L₂ terminals).

Read the Detailed Post about: How to Toggle Electric Water Heater Between 120V and 240V?

Double Pole & 4-Way Switches look similar but they are different. Both have 4 terminal screws. Keep in mind that double poles switches are rated for 220V to 240V while 4-Way switches are always rated for 120V to 277V. In addition, when the position of the 4-way switch is changed, it reverses both wires to opposite terminals and when the position of the double pole switch is changed, it turns both wires On or OFF. It is recommended to check the device rating or at least check using a multimeter in continuity test mode to verify the terminals.
The brass screws should be connected to the Hot (line, live or phase) wire using the IEC & NEC Wire color codes.
The green screw should be connected to the ground / earth wire (Green/Yellow or naked wire)
If there are no color coded screws on outlets, refer to the user manual or contact a licensed electrician.
Neutral Wire is not required in 240V outlets wiring (US). Also, Neutral is never connected to the switches.
Use the suitable voltage and ampere rating of switch with appropriate wire size and proper size MCB according to the load rating.

Precautions:

Switch off the main circuit breaker to make sure the power supply is OFF before wiring an existing or new outlet or switch with an electrical/junction box.
Contact the authorized and licensed electrician for switch installation if you are not sure about the wiring diagrams.
The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in the wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.

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