Safety interlock switch for machine guard doors

01

Pick the interlock type and coding level, and prevent defeat

ReeR's summary of ISO 14119:2013 groups interlocking devices into type 1 (uncoded cam or hinge switches), type 2 (coded mechanical actuators such as a shaped tongue), type 3 (uncoded inductive, magnetic, capacitive, ultrasonic or optical), type 4 (coded magnetic, RFID or optical) and type 5 (trapped-key). It defines low, medium and high level coded actuators as having 1 to 9, 10 to 1,000 and more than 1,000 code variations. [1]

ReeR explains that ISO 14119 defines defeat as making an interlock inoperative or bypassing it, and lists measures against it: mounting out of reach, shielded or hidden; coded devices so actuators cannot be substituted; welding, gluing or riveting so the device cannot be moved; status monitoring or cyclic testing; and a second device on a different principle with a plausibility check. It notes that the standard's table 3 sets the additional measures by device type, and that guards must not be easy to bypass under Directive 2006/42/EC. [1]

ReeR also notes that NC contacts of two or more interlocks wired in series are taken as 60% diagnostic coverage, allowing PL d but not PL e, because faults can be masked, and that the access time to the hazard must be compared with the system's stopping performance using approach speeds from ISO 13855. [1] Editorial note: tell the supplier how many guards share a safety input and the stopping time of the machine before choosing between series-wired switches and individually monitored or electronic devices.

Give the supplier the guard type (hinged, sliding, lift-off), entry direction and door alignment, required performance level, whether guard locking is needed and why (stopping time, run-down), coding level wanted, how many guards share a safety input, supply and contact ratings, cable entry or connector, environment (washdown, temperature, vibration) and certificates required.

02

Check guard locking, positive opening and reliability data

ReeR states that ISO 14119 treats interlocking and guard locking as two separate safety functions whose required performance levels may differ, and that where guard locking relies on fault exclusion its specified holding force (FZH) must withstand the static forces expected on the locking bolt. [1] Rockwell lists its TLS-Z GD2 guard-locking switch as a type 4 device with high (unique) RFID coding per ISO 14119, PL e Cat 4, locking force up to 2,000 N, power-to-release or power-to-lock versions, and PFHD 1.70E-09. [4]

For tongue switches, IDEM's KOBRA KM lists positive-break contacts to EN 60947-5-1, 8 mm travel for positive opening, B10d of 2.5 × 10⁶ operations at 100 mA, MTTFd of 356 years at 8 cycles per hour around the clock, maximum approach and withdrawal speed of 600 mm/s, IP67, −25 to +80 °C, and an optional 40 N actuator holding version. [2] IDEM's IDIS-1 achieves positive actuation at 5 mm withdrawal and warns never to use the switch as a mechanical stop, using guides and stops to protect switch and actuator. [3]

Editorial calculation: 8 cycles per hour for 24 h × 365 days is 70,080 operations a year; with B10d = 2.5 × 10⁶, MTTFd = B10d / (0.1 × 70,080) ≈ 357 years, matching IDEM's 356 years, and the switch reaches its B10d count in about 2.5 × 10⁶ / 70,080 ≈ 36 years. At 60 cycles per hour the same switch reaches it in under 5 years. [2] Use your actual guard opening rate.

03

Interlock switches sold within wider safety device ranges

Listings include safety interlock switches alongside light curtains, safety mats, safety edges and safety relays; ask each for ISO 14119 type and coding level, positive-opening data, B10d or PFHD, and certificates.

04

Actuator, head, contacts, locking solenoid and fixings

The actuator row fixes the ISO 14119 type and coding level, and ReeR notes that the standard's table 3 sets the additional anti-defeat measures by device type. [1]

05

Contact ratings, life, force and enclosure data for an interlock order

Read the life rows against your guard opening rate: the KM reaches its B10d count in about 36 years at 8 cycles per hour but in under 5 years at 60. [2]

06

Send the guard, safety level and environment together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Guard: [hinged; sliding; lift-off; alignment]
Safety: [required PL; guard locking needed; stopping time]
Device: [ISO 14119 type; coding level; anti-defeat measures]
Wiring: [guards per input; contacts; connector]
Use: [openings per hour]
Environment: [IP; temperature; washdown; vibration]
Documents: [B10d or PFHD; certificates]

See manufacturer records Send an enquiry through CNFX