reverse forward circuit diagram
This is a free printable reverse forward circuit diagram: download the diagram as SVG or open it and print to paper or PDF.
A reverse-forward circuit diagram is essentially equivalent to forward-reverse wiring, illustrating interlocked contactor control for bidirectional three-phase motor operation. The diagram shows two interlocked contactors where forward contactor positions U-V-W phase leads directly to the motor, while reverse contactor swaps two phase leads (typically V and W) reversing the rotating magnetic field. The mechanical interlock is critical: a spring-loaded arm on each contactor prevents simultaneous engagement, protecting the motor from phase-to-phase short circuits. The diagram demonstrates safe three-phase motor control in applications requiring rapid direction changes: conveyor systems changing load direction, reversible hoists, and production machinery. Both forward and reverse push buttons connect through the interlock logic, preventing accidental simultaneous activation through pushbutton design: releasing forward button must occur before reverse button functions. Modern circuits add electrical interlocks through auxiliary contacts, providing redundant protection. The diagram clearly shows the interlock mechanism and how three-phase sequence inversion (from U-V-W to U-W-V) produces rotation reversal.
Forward bias and reverse bias are foundational concepts in semiconductor electronics and are distinct from the motor forward/reverse control topic covered elsewhere on this site. In a forward-biased p-n junction the positive supply connects to the p-type material, lowering the potential barrier and allowing current to flow; in reverse bias the polarity is swapped, widening the depletion region and blocking current (until breakdown voltage is reached). Circuit diagrams illustrating both conditions are a staple of electronics coursework. You can draw and annotate p-n junction and diode circuit diagrams free in the browser at Circuit Diagram Maker.
How to wire reverse forward circuit diagram
- Isolate and lock out supply Switch off and lock out the 3-phase incomer before touching any terminals. Test with a multimeter to confirm all three phases are dead.
- Wire main power contacts Connect L1, L2, L3 through KM1 to motor terminals T1, T2, T3 for forward. For KM2 reverse output, swap T2 and T3 only — T1 stays in the same position.
- Install the thermal overload relay Wire the overload relay in series between the contactor output and motor terminals. Set the trip current dial to match the motor nameplate FLA rating.
- Wire the control circuit Wire the NC stop button in series with the circuit. Branch from there to each forward and reverse NO pushbutton, each feeding their respective contactor coils.
- Install electrical interlocks Insert KM1's NC auxiliary contact in series with KM2's coil. Insert KM2's NC auxiliary contact in series with KM1's coil. This prevents simultaneous energisation.
- Install mechanical interlock Fit the mechanical interlock bar between KM1 and KM2 per the contactor manufacturer's instructions. Operate both buttons by hand with supply off to confirm the bar prevents double-closing.
- Test under power Energise, press forward, confirm correct rotation. Stop fully, press reverse, confirm opposite rotation. Test the interlock by pressing both buttons simultaneously — neither should close.
Frequently asked questions
Why do I need both mechanical and electrical interlocks?
Electrical interlocks alone can fail if contacts weld shut. Mechanical interlocks physically prevent both contactors closing at once, which would dead-short two phases and blow your switchgear. Always use both — it is the only safe approach.
Can I switch directly from forward to reverse without stopping?
No. Always stop the motor fully before reversing direction. Plugging a running motor straight into reverse causes massive inrush current, trips your overload, and stresses the shaft coupling. Wire in a time-delay relay if you need fast direction changes.
What size contactors do I need?
Match the contactor AC3 current rating to your motor full-load ampere rating with a safety margin of at least 10%. Undersized contactors overheat and weld closed, which defeats your interlocks entirely.
How do I wire the interlock contacts?
Wire KM1's NC auxiliary contact in series with KM2's coil circuit, and KM2's NC auxiliary contact in series with KM1's coil circuit. When either contactor energises, it breaks the other's coil supply before the second can close.
My motor reverses but trips the overload immediately. Why?
Check that phases L2 and L3 are the only two swapped at KM2's output terminals — L1 stays the same. If you accidentally swapped L1 and L2 instead, the phase sequence is wrong and motor current spikes. Verify with a phase rotation meter.
What does a circuit diagram for forward bias and reverse bias show?
A forward bias circuit diagram shows a DC supply with its positive terminal connected to the p-type side of a p-n junction diode and its negative terminal to the n-type side, with a series resistor to limit current; an ammeter in the loop confirms conventional current flows through the diode. A reverse bias circuit diagram reverses the supply polarity — positive to the n-type, negative to the p-type — and the ammeter shows only negligible leakage current because the depletion region is widened. Both diagrams are commonly drawn side by side in physics and electronics textbooks to contrast the conducting and non-conducting states of the junction.
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