Wiring an Emergency Stop on a Hitachi WJ200 VFD for Lathe Safety

Overview: WJ200 Lathe E-Stop Engineering Requirement

A belt-driven metal lathe retrofit with a Hitachi WJ200 variable-frequency drive must meet two distinct safety functions that are often conflated. The first is a Category 0 / Category 1 emergency stop that removes torque from the spindle motor as quickly as is electrically safe, ideally with the assistance of the drive's external brake resistor so that the spindle does not coast. The second is an unattended-start protection function that prevents the spindle from being energized while the operator has hands on the chuck, on the step-pulley belt, or inside the headstock enclosure. Both functions can be implemented in the WJ200, but they require different hardware paths, different parameter settings, and different acceptance-test procedures.

The application described here is a Jet 13x40 (or equivalent 13-inch x 40-inch gear-head / belt-drive lathe) fitted with a smaller motor pulley so the drive can be operated up to 120 Hz for low-end spindle speeds, and an external dynamic brake resistor mounted at the drive's P and BR terminals. The carriage-mounted control lever is a three-position (forward / stop / reverse) maintained switch wired in a classic three-wire control configuration. The retrofit must preserve that lever and add a clearly-marked emergency-stop palm button that mechanically overrides any drive command.

WJ200 Safety Architecture and I/O Map

The WJ200 series (sold in the Americas as a Yaskawa product following the 2014 merger with Hitachi Industrial Systems) provides three independent control paths that can be used singly or in combination to satisfy an emergency-stop requirement. The relevant terminals on the control terminal strip are summarized below.

The GS1 / GS2 pair is the only path on the WJ200 that physically disables the IGBT gate drive. Any other stop method (logic low on FW or RV, external trip input, coast-to-stop from a multi-function input) merely commands the drive to decelerate or output zero torque via firmware, and a faulted IGBT module could still conduct. For an emergency-stop function on a turning machine, GS1 / GS2 is therefore the engineering-preferred implementation provided the firmware variant on the drive supports the unattended-start protection function described in the WJ200 manual (page 34 in the printed manual shipped with current-production units).

Prerequisites

1. Confirm the WJ200 firmware version supports the GS1/GS2 safe-stop function. The hardware-enable DIP switch (typically SW1 position 4 or SW2 on later revisions, refer to the WJ200 quick-reference guide) must be present on the control board; older WJ200-001S / -002S units built before the safety-function TÜV approval may have a blank or reserved page in the manual.
2. Verify that the motor nameplate FLA is below the WJ200 continuous rating at 120 Hz operation, and that the constant-torque region (up to 50 Hz) covers the heaviest cut. A WJ200-022SF (3 HP, 230 V, single-phase input) typically delivers 9.6 A continuous and is suitable for a 2 HP lathe motor with margin.
3. Install a dynamic brake resistor rated for the worst-case deceleration. Hitachi / Yaskawa external braking resistors for the WJ200 include 3G3IV-PERF15WJ (for 200 V class, 1.5 kW drive) and equivalent; size for at least 150 % of the drive's continuous rating for 10 s, since an E-stop with the spindle rotating is the worst-case duty.
4. Select an E-stop device with positive-opening contacts per IEC 60947-5-5, rated for at least 1 A at the logic voltage used. A 22 mm or 30 mm twist-to-release palm button (IDEC HW1B series, Eaton M22-PV/K20, or equivalent) provides a maintained NC contact pair suitable for either GS1/GS2 or the L-source interlock.
5. Document the control voltage. The default WJ200 sink/source logic is 24 VDC, which is convenient because the E-stop contact drops directly into the GS1/GS2 loop without an interposing relay.

Wiring Method A: GS1/GS2 Hardware Safe-Stop (Preferred)

This implementation uses the drive's safety inputs to inhibit IGBT firing while the external brake resistor dissipates the spindle kinetic energy. The spindle stops on the drive's deceleration ramp, which is configured for the shortest time that does not trip an over-voltage (OV) fault on the DC bus.

1. Enable the safety function at the drive. Locate DIP switch SW1 (or equivalent per hardware version) and move position 4 to ON. The WJ200 manual describes this as the SW (function switch for safety / unattended start protection); on power-up the drive will display the safety-mode banner.
2. Wire the E-stop NC contact in series between GS1 and GS2 (or between each input and the PLC terminal). The two-channel topology protects against a single contact welding closed.

   +24V_ref -----------[ NC E-STOP ]--- GS1
                          |
                          +------------- GS2
                                       (return is PLC terminal internally)

3. Set the deceleration ramp short enough to engage the brake resistor aggressively but long enough to avoid OV trips. Typical lathe settings: b003 (deceleration time 1) = 1.0 to 3.0 s, with b090 (dynamic braking usage ratio) = 50 % or higher. b095 (dynamic braking enable) = 01 (enable during run).
4. Verify that fault output relay C011 is configured to drop out on the safety stop so an upstream contactor or indicator can follow. c021 = 05 (fault) is the standard assignment.
5. Set the multi-function input that is no longer required for external trip (input 3, function code 11, EXT) to 00 (no function) so that firmware-driven external trips do not conflict with hardware GS1/GS2.

When the operator presses the E-stop, both GS1 and GS2 open, the gate driver is inhibited, and the spindle decelerates as energy is dumped into the external resistor. The drive latches in the safe state; to restart, the operator must release the E-stop (twist-to-release) and issue a fresh FW or RV command from the carriage lever.

Wiring Method B: L-Source Interlock (Three-Wire Control)

When the GS function is unavailable or has not been TÜV-approved on the specific firmware build (the WJ200 manual page for the emergency-stop function may carry a "to be finalized after TUV approval" notice on early revisions), the L-source interlock is the next-best engineering option. It interrupts the internal 24 VDC source that feeds the forward and reverse command terminals, so neither FW nor RV can energize while the E-stop is pressed. Because the IGBTs are not inhibited, firmware still commands a controlled deceleration into the brake resistor.

1. Identify the source/sink DIP switch on the WJ200 control board and set it to source so that the FW and RV terminals source current from L through the external switches.
2. Wire the carriage lever's forward and reverse contacts between L and terminals 1 and 2 respectively, with the stop position open.
3. Insert the E-stop NC contact in series with L so that opening the E-stop removes the source voltage to the lever entirely.

            +---[ NC E-STOP ]---+--- L (drive internal 24V)
                                |
        carriage lever  +-------+--------[ FW contact ]----- terminal 1 (FW cmd)
                                |
                                +--------[ RV contact ]----- terminal 2 (RV cmd)

4. Configure parameters b001 = 00 (terminal 1 = forward), b002 = 01 (terminal 2 = reverse), b003 (accel) and b004 (decel) per the lathe mechanics. For a 2 HP lathe motor with significant spindle inertia, b004 = 1.5 to 4.0 s is typical.
5. Assign multi-function input 5 (terminal 5) to the reset function (code 04, RS) so a fault can be cleared without reaching into the cabinet.

Operationally the operator pushes the carriage lever to forward, the FW contact closes, terminal 1 sees 24 V, and the drive ramps the motor up to the commanded frequency. Pressing the E-stop pulls L down, both terminal 1 and terminal 2 go to high impedance, and the drive executes the configured deceleration using the brake resistor. The drive enters a STOP state and will not restart until the lever is returned to the neutral (stop) position and a new run command is issued.

Wiring Method C: Direct Input Power Disconnect (Backup Method)

This is the most conservative implementation and is appropriate when the drive does not yet have an approved safety firmware build, when the operator wants belt-and-suspenders redundancy, or when a third-party safety relay (such as an Omron G9SX-GS226-T15-RC or an Allen-Bradley MSR127 safety monitoring relay) is required by a risk assessment.

1. Install a two-pole contactor (or a three-pole for three-phase input) in line with the WJ200 input power. The contactor coil is driven from the same 24 VDC control supply that powers the drive's L terminal, or from a separate fused 120 VAC source.
2. Wire the E-stop NC contact in series with the contactor coil so that pressing the E-stop de-energizes the contactor and removes input power to the drive entirely.
3. Add an auxiliary contact from the contactor to the drive's reset circuit (or to a multi-function input programmed as External Trip, code 11) so that the drive does not auto-restart when input power is reapplied while the carriage lever is in forward.

  AC mains ---[ line contactor ]---+---> WJ200 L1 / L2 / L3 input
        ^                          |
        |                          +---> WJ200 L1 / L2 only (single-phase units)
   NC E-STOP -- contactor coil A1 -- coil A2 (neutral)

This method produces the longest spindle deceleration time because the drive powers down with its DC bus collapsing and no active braking; the spindle coasts. For a small lathe with limited inertia this is acceptable, but for a heavy spindle the operator may need to add a mechanical spindle brake as well. The Hitachi WJ200 Quick Reference Manual wiring example (page 93) shows exactly this topology as an "emergency stop wiring example" and is the recommended fallback whenever GS1/GS2 is not available.

Integrating the 3-Wire Carriage Control Lever

A three-wire (or three-position) carriage lever is wired so that moving the lever up closes the reverse contact (energizing terminal 2), moving it down closes the forward contact (energizing terminal 1), and the center position opens both contacts. There is no maintained RUN contact; the lever itself provides the "start" command. This is functionally identical to the WJ200 manual's page 31 example and is the recommended topology for a lathe because it provides an inherent zero-energy center position.

When combined with the L-source interlock, the complete electrical path is:

   Drive L ---[ NC E-STOP ]---+----[ lever REV contact ]----- terminal 2 (RV)
                              |
                              +----[ lever FWD contact ]----- terminal 1 (FW)
                              |
                              +----[ optional: lever center OFF ]----- (no connection)

The lever's mechanical detent at the center position is part of the safety case: a spring-return lever is preferred over a maintained lever for an E-stop application because the operator cannot leave the lathe with the lever in forward and walk away. If the existing lever is maintained, replace it with a spring-return unit or add a separate stop pushbutton in the lever path.

DIP Switch and Parameter Configuration Summary

Always perform a parameter save (write to EEPROM via the b180 copy command) after commissioning so that the values survive a power cycle.

Commissioning and Functional Verification

1. With input power removed, verify continuity across the E-stop contact when released (should be closed) and open-circuit when pressed (should be open). Measure across both poles to confirm both channels of a two-channel device operate.
2. Apply input power and confirm the drive initializes without an E-trip indication. The display should show the standard run-mode screen.
3. With the E-stop released, jog the drive from the keypad at low frequency (5 Hz) in both directions and confirm correct rotation. Then issue a stop and confirm the motor decelerates within the configured ramp.
4. Press and hold the E-stop while commanding forward. The drive must immediately enter the safe-stop state (GS1/GS2 method) or command the controlled deceleration (L-source method). Verify the spindle stops within the time window allowed by the risk assessment; record the actual stop time.
5. Release the E-stop. The drive must remain in the stop state until a fresh run command is issued. This is the unattended-start protection.
6. Power down the drive with the carriage lever in the forward position. Restore power. Confirm that the drive does NOT start automatically. This validates the unattended-start protection after power-cycle.
7. Repeat steps 4 through 6 for the reverse direction and for combinations (forward then reverse while running).
8. Measure the dynamic brake resistor temperature after 10 consecutive E-stop cycles to confirm it stays below the resistor's thermal rating. A resistor rated for 10 % duty cycle will overheat quickly if the operator uses E-stop as a normal stop.

Troubleshooting Matrix

Comparison of E-Stop Methods

Method A is the engineering best practice when the firmware supports it. Method B is a robust fallback that is acceptable for non-CE hobby or educational installations. Method C is appropriate when a third-party safety relay or a Category 3 / PLe risk assessment is mandated.

Selection Considerations Beyond E-Stop

Choosing the E-stop topology should be done in the broader context of VFD selection. Control Engineering's "Five Questions to Ask When Selecting a VFD" highlights application match, power source characteristics, enclosure rating, environment, and service / support as the dominant criteria. For a shop-floor lathe, those questions map directly onto the safety architecture: a drive with a built-in hardware safe-stop (such as the WJ200 with GS1/GS2) answers the safety question before the enclosure and service questions are even addressed. A drive without that function forces the safety burden onto external contactors and safety relays, raising cost and reducing the operator's ability to confirm safe state from a glance at the drive keypad.

FAQ