How to wire a conveyor belt's electrical box (frequency inverter, E-stop, direction control)

thijs · September 2, 2026, 12:15am

Based on contributions by ThomasVrakking.

This describes the electrical wiring inside a typical conveyor belt control box: mains power in, safety switching, the frequency inverter (VFD) that drives the motor, and the E-stop / run / direction control wiring. Use it as a reference when building or troubleshooting a conveyor’s electrical box.

This is a mains-voltage (230 V AC) wiring job. Have the wiring checked by a qualified electrician before switching anything on, and always work with the main switch off.

What you need

Conveyor with a three-phase motor and a frequency inverter (this guide was written for a Mitsubishi FR-D720S-025SC-EC; the terminal names are similar on most Mitsubishi FR-D700 series drives)
Main switch
Circuit breaker
Distribution block(s) for phase/neutral and for earth
Potentiometer (for manual speed control)
Emergency stop switch
Run/stop and direction switches
The inverter’s manual, for your exact terminal layout and parameter settings

Steps

1. Power supply connection

Connect the 230 V AC supply (from a wall socket) to a main switch.
The main switch splits the incoming power into:
- Phase (L)
- Neutral (N)
- Earth (PE – green/yellow)

2. Safety and distribution

Connect the output of the main switch to a circuit breaker.
From the circuit breaker, wire to a distribution block.
From the distribution block:
- Phase (L) and Neutral (N) go to the input terminals of the frequency inverter (VFD).
- The earth wire (green/yellow) goes to a separate earth distribution block, then to the earth terminal of the VFD.

Check: the original build used a circuit breaker without an earth-leakage (RCD) function, because the lab’s fixed installation already has upstream RCD protection. If you set this conveyor up outside the lab, you must add earth-leakage protection to the circuit breaker yourself.

3. Connecting the frequency inverter (FR-D720S-025SC-EC)

Connect the three-phase motor directly to the inverter’s output terminals U, V, W, and connect the motor’s earth to the VFD’s PE terminal.

4. Control wiring

Potentiometer connection (for manual speed control):
- Terminal 2: wiper (variable output from the potentiometer)
- Terminal 5: ground (GND)
- Terminal 10: potentiometer supply ( Check: the exact voltage/function of terminal 10 was not recorded in the original build notes — confirm against the FR-D700 wiring diagram before connecting)
Emergency stop switch:
- Connect the normally-open (NO) contacts of the E-stop to terminals S1 and S2.
- Terminal SC is the common return.
Run/stop and direction control (via switches):
- Terminal PC: common (connected to one side of both switches)
- Terminal STF: forward run command
- Terminal STR: reverse run command

Important notes

The electrical box may contain extra components (a relay, an electrical socket, a 230→24 V power converter, a Mitsubishi servo amplifier) that are not needed to make the conveyor run — you’re free to use them for your own project, but you can ignore them for basic conveyor operation.
Use safety rings and screws to attach the motor cap correctly.
Always verify that the control terminals are configured correctly in the VFD’s parameters (e.g. set the input mode so STF/STR are used for run/direction).
Follow the manufacturer’s official manual for the exact parameter settings and safety precautions for your inverter model.
Have all wiring work done or checked by a qualified electrician, and make sure it complies with local electrical codes.