{"id":1660,"date":"2026-09-26T19:10:00","date_gmt":"2026-09-26T11:10:00","guid":{"rendered":"https:\/\/lemaele.com\/blog\/polarity-reversing-toggle-switch-guide\/"},"modified":"2026-09-26T19:10:00","modified_gmt":"2026-09-26T11:10:00","slug":"polarity-reversing-toggle-switch-guide","status":"publish","type":"post","link":"https:\/\/lemaele.com\/de\/blog\/polarity-reversing-toggle-switch-guide\/","title":{"rendered":"Verbindungshandbuch f\u00fcr DPDT-Polartransistor-Schaltkontakte"},"content":{"rendered":"

A DPDT toggle switch can reverse the polarity applied to a two-wire permanent-magnet DC motor by swapping both motor connections at the same time. In a common six-terminal layout, connect the motor to the two center common terminals and arrange the positive and negative supply on opposite outer corners so the two switch positions exchange polarity. The terminal view is not universal: identify common and throw terminals from the exact switch drawing or with a continuity meter before wiring.<\/p>\n

This is a circuit-topology explanation, not approval to switch a particular motor directly. DC motor startup and stall current can be much higher than running current, and a motor is an inductive load. The LEMA LT2210C product information shown for this example lists AC ratings; it does not establish a DC motor switching rating. Use a DPDT part with a published DC rating for the actual motor duty, or use a properly rated relay\/contactor or motor driver.<\/p>\n

\"LEMA
Actual LT2210C product image. It identifies a three-position DPDT product; confirm the exact wiring diagram and DC load rating separately.<\/figcaption><\/figure>\n

What DPDT means in a reversing circuit<\/h2>\n

DPDT means double pole, double throw: the switch controls two separate paths, and each pole can connect its common terminal to one of two throws. In a polarity-reversing circuit, the two poles change both motor leads together. One switch position applies positive to motor lead A and negative to lead B; the other position swaps those connections. Reversing the voltage polarity across a brushed permanent-magnet DC motor reverses its direction, as SparkFun\u2019s DC brush motor guide<\/a> explains.<\/p>\n

A switch marked ON-OFF-ON has a third, center detent that disconnects both poles. That is often useful for a manual forward-stop-reverse control, but \u201ccenter off\u201d is not the same as an electrical interlock or a safe stop function. A motor may coast, a load may move under gravity, and the mechanism may require braking or a separate safety circuit.<\/p>\n

Do not confuse this with reversing an AC motor. Single-phase and three-phase motor direction changes depend on winding connections and motor design; the simple two-wire polarity reversal below applies to a compatible brushed DC motor, not to arbitrary AC, brushless, stepper, or electronically commutated motors.<\/p>\n

First identify the six terminals<\/h2>\n

Manufacturers do not use one universal terminal numbering convention. A six-terminal toggle may place the two commons in the center of the rear view, but a different view direction, terminal arrangement, or internal construction can change what a drawing appears to show. Start by finding the model-specific circuit diagram and identify two commons plus four throws. If the diagram is unavailable, test the unpowered switch with a continuity meter in every lever position.<\/p>\n

For each pole, the common terminal should connect to one throw in one ON position and the other throw in the opposite ON position. On an ON-OFF-ON version, neither throw should connect to the common in the center OFF position. Mark the terminal side and orientation on a sketch; do not assume the lever side and wiring side have matching left\/right orientation.<\/p>\n

\"LEMA
Terminal styles vary by version. The drawing must match the exact part and view orientation used in the wiring plan.<\/figcaption><\/figure>\n

Conceptual six-terminal wiring map<\/h2>\n

The table below describes a common rear-view layout where the two center terminals are the pole commons and each row is one pole. It is a logical example only. Confirm that the actual switch matches this arrangement before connecting a supply. Label terminals by measured function rather than relying on the positions shown in a generic diagram.<\/p>\n\n\n\n\n\n\n\n\n\n\n
Rear-view position<\/th>\nConnection<\/th>\nPurpose<\/th>\n<\/tr>\n<\/thead>\n
Upper-left outer throw<\/td>\nSupply positive (+V)<\/td>\nFirst polarity feed for pole A<\/td>\n<\/tr>\n
Upper-center common<\/td>\nMotor lead A<\/td>\nOutput from pole A<\/td>\n<\/tr>\n
Upper-right outer throw<\/td>\nSupply negative (0 V)<\/td>\nOpposite polarity feed for pole A<\/td>\n<\/tr>\n
Lower-left outer throw<\/td>\nSupply negative (0 V)<\/td>\nFirst polarity feed for pole B<\/td>\n<\/tr>\n
Lower-center common<\/td>\nMotor lead B<\/td>\nOutput from pole B<\/td>\n<\/tr>\n
Lower-right outer throw<\/td>\nSupply positive (+V)<\/td>\nOpposite polarity feed for pole B<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

With the handle selecting the left throw pair, motor lead A receives +V and lead B receives 0 V. Selecting the right throw pair swaps the two motor connections. In the center detent, an ON-OFF-ON switch leaves both commons disconnected. If the motor runs opposite to the machine\u2019s intended \u201cforward\u201d label, de-energize the circuit and swap the two motor leads or redefine the machine direction convention; do not change the supply wiring while energized.<\/p>\n

The same topology is often drawn as a cross-over or \u201cX\u201d wiring diagram. DigiKey\u2019s DPDT polarity-reversal discussion<\/a> is a useful visual reference. Compare its terminal numbering with the drawing supplied for your actual switch before translating any numbered pins.<\/p>\n

Check the load before switching the motor directly<\/h2>\n

A polarity-reversing switch must handle both poles\u2019 electrical duty. Determine the motor\u2019s rated voltage, normal running current, startup current, stall current, direction-change frequency, and the time spent reversing. A loaded mechanism can demand more torque and current than an unloaded motor on a bench. Check the motor datasheet and measure the actual assembly when the manufacturer\u2019s data does not cover the complete load.<\/p>\n

When contacts open, a motor\u2019s inductance can produce a voltage transient. At DC, there is no periodic zero crossing to help extinguish the opening arc. Reversing while a motor is still spinning can also create a high current and mechanical shock. A center-off position gives a manual pause, but it does not guarantee that an operator waits long enough for the motor to stop. The control design may need a coast interval, interlock, braking circuit, current limit, or an appropriately engineered motor controller.<\/p>\n

Choose an electrical rating that explicitly covers the supply type, voltage, motor load, and expected switching life. The LEMA LT2210C product page<\/a> identifies an ON-OFF-ON three-position DPDT switch and shows 15 A at 250 V AC and 20 A at 125 V AC. Those AC figures do not establish a DC motor rating. Do not convert them into a guessed DC number. If no suitable DC rating is published, request written technical confirmation or use a suitably rated relay\/contactor or an H-bridge motor driver.<\/p>\n

For larger loads, the toggle may operate only a control input or relay coil while properly rated power contacts handle the motor. A relay solution still needs coordinated forward\/reverse interlocking so the two directions cannot energize together. A semiconductor H-bridge can provide controlled reversal and current limiting, but it introduces its own voltage, current, thermal, and protection requirements.<\/p>\n

Bench verification before applying power<\/h2>\n
    \n
  1. Disconnect all power and label the switch\u2019s terminal-side orientation.<\/li>\n
  2. Use the product diagram or meter to identify the two commons and each pole\u2019s two throws.<\/li>\n
  3. Check continuity in the first ON position, the center OFF position, and the second ON position.<\/li>\n
  4. Confirm that the crossover wiring yields opposite polarity at the two motor output terminals in the two ON positions.<\/li>\n
  5. Check for an unintended short between supply positive and negative before connecting the motor.<\/li>\n
  6. Use a current-limited low-voltage test setup first, with the motor mechanically unloaded and guarded.<\/li>\n
  7. Verify the machine\u2019s forward\/reverse labels, center-off behavior, interlock, and stopping distance in the complete assembly.<\/li>\n<\/ol>\n

    Do not use a continuity buzzer as the only acceptance test for a power circuit. It can show contact state but not prove that the part can switch the intended current, interrupt an inductive load, or meet the required lifetime. Electrical qualification must use the application\u2019s actual voltage, current, and duty.<\/p>\n

    Common mistakes<\/h2>\n