Electric Hoist Safety Devices: Overload Limiter & Limit Switch
Complete Guide to Electric Hoist Safety Devices The legally required safety devices on an electric hoist include: an Overload Limiter (tripping at ≤110% of Rated Lifting Capacity), a hoisting limiter (dual-stage protection via Travel Switch + power-off limit switch), a Hook Latch (spring-loaded flange), and an Emergency Stop Button (red mushroom-head, self-locking, normally closed contact). Additional mandatory equipment includes a Buffer, rail end stops, Undervoltage Protection, Zero Position Protection, Phase Sequence Protection, and Earthing Protection. Per GB 6067.1-2010, the crane must cease use immediately if any safety device fails.
Electric hoists are classified as special equipment, and national regulations mandate a full suite of safety protection devices. Each device serves a distinct function, has a specific installation position, adjustment method, and inspection interval. This article addresses the five most frequently searched questions about electric hoist safety devices—covering configuration requirements, adjustment methods, and connection modes—to help equipment managers ensure compliant installation, correct usage, and periodic inspection.
Electric Hoist Safety Devices: FAQ
What safety devices are fitted on an electric hoist?
| safety device | Function | According to Standard | inspection interval |
|---|---|---|---|
| Overload Limiter | overload Cut off when Hoisting / Lifting Circuit, Only allowed Lowering | GB 6067.1-2010 | Every six months |
| hoisting limiter | Uplimit switch Cut off hoisting, LSBPosition cut-off Lowering | ISO 4301 Crane Design Standard-2008 | Daily |
| Hook Latch | Prevent Wire Rope From Hook Disengagement from | GB 6067.1-2010 | Daily |
| Emergency Stop Button | emergency situation Main disconnect Power Supply | IEC 60204-32 | Daily |
| Buffer | Absorbtrolley Impact energy | ISO 4301 Crane Design Standard-2008 | Monthly |
| Crane Railend stop | Prevent Hoist From Crane Rail Disengagement at both ends | GB 6067.1-2010 | Monthly |
| Undervoltage Protection | No self-restart after power recovery | IEC 60204-32 | Every six months |
| Zero Position Protection | Before starting Controller Must be at zero position | IEC 60204-32 | Every six months |
| Phase sequence/Phase Loss Protection | Cut off on phase reversal or phase loss Power Supply | ISO 4301 Crane Design Standard-2008 | Every six months |
| Earthing Protection | Metal enclosure Grounding Protection against electric shock | IEC 60204-32 | Annually |
All safety devices must be kept in good working condition. If any device fails, cease use immediately and report for repair. Inspection intervals must follow TSG Q0002-2008 Safety Technical Supervision Regulation for Lifting Appliances.
How to Adjust the Overload Limiter on an Electric Hoist?
Overload Limiter Calibration Procedure (Torque Sensor / Electronic Type):
① Preparation: Prepare Standard Weights at 100%, 110%, and 125% of the Rated Lifting Capacity. Ensure the hoist is under No-load and the Power Supply is normal.
② No-load Zeroing: Power on the Overload Limiter and press and hold the calibration key to enter parameter settings. With no load applied, press the "Zero" key to set the current weight to 0.
③ Load Calibration: Lift the Test Weight equal to 100% of the rated load. Once stable, press the "Calibrate" key and confirm the displayed value matches the weight. If the error exceeds ±5%, adjust the gain parameter.
④ Set Alarm Thresholds: Set the early warning value at 100% (audible and visual alarm), the action value at 110% (cuts the Hoisting circuit, allowing Lowering only), and the immediate action value at 125% (emergency shutdown).
⑤ Verification: Lift a 110% rated load and confirm the Overload Limiter activates, stopping Hoisting while permitting Lowering. Lift a 125% load to confirm emergency shutdown.
⑥ Sealing: After successful calibration, seal the Overload Limiter's Cover plate to prevent unauthorized adjustment. Record and archive each calibration session.
Note: Mechanical Overload Limiters (spring compression type) set the action value by adjusting the spring Preload. Each full turn of the adjusting Nut changes the action value by approximately 5%. Electronic types are configured via the instrument panel menu; procedures vary slightly by manufacturer (common brands: Changsen JC-1C, Yichang SY-1A, Kaiji KG-2). The calibration interval for Overload Limiters is once every six months. Re-calibration is mandatory after replacing the Sensor. Bypassing or removing the Overload Limiter to forcibly lift overweight loads is a serious violation and will result in shutdown for rectification and fines as per TSG Q0002-2008.
How to Adjust the Hoisting Limiter on an Electric Hoist?
Hoisting Limiter Adjustment Procedure (Two-Stage Limit):
Stage 1: Travel Switch Adjustment
① Loosen the fixing Bolts on the Travel Switches (SQ1/SQ2). ② Manually raise the Hook to the desired upper limit position (top edge of the Hook at least 200mm from the Drum). ③ Adjust the SQ1 trip flange so it just touches the switch roller; activation is indicated by a "click" sound. ④ Tighten the Bolts and verify manually — when the flange pushes the roller, the Hoisting Contactor KM1 coil should de-energize (Hoisting stops), while Lowering via KM2 should remain operational. ⑤ Adjust the SQ2 lower limit similarly (leaving at least 3 turns of Wire Rope on the Drum).
Stage 2: Power-Off Limit Switch Adjustment
① The actuating rod of the power-off limit switch is driven by the hook nut or a Counterweight block. Adjust the gap between the rod and the hook nut: under normal conditions, when the Hook reaches its highest point, the hook nut should push the rod to open the internal normally-closed contact. ② If it triggers too early (stopping while there is still significant Hoisting travel left), move the rod closer to the Hook. If it triggers too late (the Hook contacts the Drum before stopping), move the rod further away from the Hook. ③ After adjustment, perform 3 full No-load test cycles to confirm correct operation of both upper and lower limits. ④ On CD1-type power-off limit switches, manual reset is required by pressing the reset lever after activation — always ensure the hook is clear of the limit position before resetting.
Adjustment Standards: When the upper limit triggers, the top edge of the Hook must be at least 200mm from the Drum (per ISO 4301 Crane Design Standard). When the lower limit triggers, at least 3 turns of Wire Rope must remain on the Drum (to prevent the rope from pulling out of its anchor point). After adjustment, always verify with power on to confirm the Hoisting/Lowering direction matches the limit switch action. Note: Limit switches are protective devices, not normal stopping devices — routine operations should always stop before the limit switch is activated.
How to Install a Hook Latch on an Electric Hoist?
Hook Latch (Anti-Detachment Flange) Installation Steps:
① Inspect the Hook: Verify that pre-drilled holes exist at the hook opening for mounting the latch (typically 2 threaded holes of M4 to M6). If no holes are present, drill them on the back of the hook tip using an electric drill (hole diameter φ5 to φ6), tap the threads, and proceed with installation.
② Selection: Hook Latches come in two types: spring-loaded (standard configuration) and bolt-type. The spring-loaded latch is stamped from spring steel and uses spring force to automatically return to the closed position. Thickness must be at least 3mm, and width must cover more than 80% of the hook opening width.
③ Installation: Align the mounting holes of the latch with the pre-drilled holes on the Hook. Insert M5 or M6 Bolts with a spring washer and Flat Washer, and tighten with a Nut (Torque approximately 8 N·m). After tightening, the latch should rotate freely around the Bolt, with spring force causing it to close automatically.
④ Verification: Manually push the latch open — it should spring back and close automatically. Test with a Wire Rope Sling: confirm the latch is pushed open as the sling enters the Hook and closes automatically once inside to prevent Load detachment. The sling should enter the Hook from below the latch to prevent the latch from being pressed against the hook wall and losing its protective function.
⑤ Inspection: The gap between the closed latch and the hook tip must be ≤3mm (per GB 6067.1-2010). Before each daily use, check the latch for Deformation, spring Failure, and loose Bolts. Replace the spring latch promptly if spring force shows signs of attenuation.
⑥ Prohibited practices: Never weld the anti-drop flange to the hook (the heat-affected zone from welding compromises hook strength); never substitute wire binding for the anti-drop device; never remove the anti-drop device (removal is a violation—per GB 6067.1-2010, Section 3.4, a hook without an anti-drop device is not permitted for use).
How to Wire the Emergency Stop Button on an Electric Hoist
Emergency Stop Button Wiring Procedure:
① Selection: The emergency stop button must be a red mushroom-head, self-latching type (with twist-to-release or pull-to-release), compliant with IEC 60204-32, Section 9.2.5.4. Contact configuration: 1NC (normally closed) + 1NO (normally open); 1NC is preferred.
② Wiring location: The NC contact of the emergency stop button is wired in series on the control circuit bus (per IEC 60204-32). Electrical sequence: Control Transformer TC secondary → Emergency Stop SB0 NC contact → power-off limit switch NC contact → handle/remote control button → KM coil → other end of TC secondary.
③ Emergency stop on the pendant handle: The emergency stop wire in the handle cable (typically black) connects to the NC terminal of the emergency stop button inside the handle; the other end of the handle cable terminates at the corresponding terminal block position in the Control Cabinet. Recommended wire gauge: 0.75mm², with crimped ferrule terminals.
④ Emergency stop on the Control Cabinet: In addition to the handle-mounted emergency stop, an emergency stop button (red mushroom head) must also be installed on the Control Cabinet panel, with its NC contact wired in series with the control circuit. The two emergency stop buttons are electrically in series—pressing either one opens the entire circuit, de-energizing all contactors.
⑤ Remote control emergency stop: The emergency stop relay K5 on the Remote Receiver uses a de-energized-to-release NC contact, also wired in series on the control circuit bus. Pressing the emergency stop on the Remote Control de-energizes relay K5 on the receiver, opening the NC contact and cutting off the control circuit.
⑥ Verification: After wiring, perform a power-on test—press the emergency stop button and all mechanisms must stop immediately; after twist-to-release reset, press the button on the handle and the mechanism resumes operation. This confirms the "stop-priority" principle: once the emergency stop is triggered, no subsequent operation can restart the hoist until a manual reset is performed.
The emergency stop circuit must use a two-wire configuration (no shared common wire) to ensure the circuit remains fully independent. A dedicated red 3-core or 4-core emergency stop cable is recommended to distinguish it from other control lines. Test the reliability of the emergency stop button daily before use: with the hoist in no-load operation, press the emergency stop and confirm immediate shutdown.
Emergency Stop Button Wiring Color Comparison Table
| Position | Recommended wire color | Wire gauge | Terminal |
|---|---|---|---|
| Handle Emergency Stop Button—NCTerminal | Black | 0.75mm² | Connect tocontrol circuit Incoming line |
| Handle Emergency Stop Button—COMTerminal | Black/Gray | 0.75mm² | Connect tocontrol circuit Outgoing line to TC |
| Control Cabinetemergency stop—NCTerminal | Red | 1.0mm² | Connected in series withcontrol circuitbus |
| Remote Control K5—NCTerminal | Red/White | 0.75mm² | Connected in series withcontrol circuitbus |
Note: Wire colors follow the recommendations of GB/T 6995-2008 Identification Methods for Wire and Cable. Actual colors may vary by manufacturer—always refer to the Electrical Schematic supplied with your unit.
Electric Hoist Safety Device FAQ
Q: Can the electric hoist safety devices be removed?
A: Absolutely not. Clause 3.2 of GB 6067.1-2010 is explicit: any crane with a failed or removed safety device must cease use immediately. The Overload Limiter, Limit Switches, Hook Latch, and Emergency Stop Button are mandatory safety protection devices. Removing or bypassing them is a serious violation—special equipment inspection will flag the unit as non-compliant and order it out of service for rectification. Operators have the right to refuse to operate if any safety device is missing.
Q: How often should electric hoist safety devices be inspected?
A: The inspection interval is set by TSG Q0002-2008: Daily before use—Limit Switches, Emergency Stop Button, Hook Latch, Wire Rope. Monthly—Buffer, rail end stops, grounding wire. Semi-annually—Overload Limiter calibration, Undervoltage Protection test, Phase Sequence Protection test. Annually—Grounding Resistance test (≤4Ω), Insulation Resistance test (≥1MΩ), and a full safety inspection of the complete unit. Every inspection must be documented and the records kept on file for at least 5 years.
Q: What happens if a missing safety device is discovered?
A: Under Article 84 of the Special Equipment Safety Law, operating special equipment without the required safety protection devices results in an order to cease use and a fine of RMB 30,000 to RMB 300,000 (approx. $4,500 to $44,500). In serious cases, the use registration certificate may be revoked. Furthermore, if personal injury or fatality occurs due to a missing safety device, company management may face criminal liability. We strongly recommend regular self-inspections to ensure all safety devices are present and functional.
Q: How many safety devices must an electric hoist have to be compliant?
A: Per GB 6067.1-2010 and TSG Q0002-2008, an electric hoist must be equipped with at least the following 10 items: Overload Limiter, upper Limit Switch, lower Limit Switch, Hook Latch, Emergency Stop Button (plus one on the Control Cabinet), Undervoltage Protection, Zero Position Protection, Earthing Protection, rail end stops, and Buffer. Every one of these is mandatory. Metallurgical, explosion-proof, and other high-hazard environments carry additional safety configuration requirements.
Q: What should I do if the Emergency Stop Button won't release after being pressed?
A: The Emergency Stop Button is a self-locking mushroom-head type—it is designed to stay locked after being pressed, so it not popping back up is normal. To release it, turn it clockwise (twist-to-release type) or pull it outward (pull-to-release type). If it still won't spring back after twisting or pulling, the internal locking mechanism may be jammed: check for debris between the mushroom head and the button housing and blow it out with compressed air. If that doesn't help, remove the button panel and inspect the internal locking slide for deformation or spring fracture, then replace the button with one of the same model. Never use pliers or a screwdriver to pry the mushroom head—this will damage the internal locking mechanism and permanently disable the emergency stop function. After replacement, always retest: press to confirm the contacts open, then release to confirm they close again.
