Intermittent Safety-Chain Shutdown and a Request to Bypass a Gate Switch
A 2012 ten-stop traction elevator, 300 fpm, VVVF drive, stops at random floors with a fault logged as 'safety chain open' and a door-lock LED that flickers. The problem is more frequent on hot afternoons and when the car passes the fourth floor. It usually resets after the main disconnect is opened and closed. The travelling cable has two spliced repairs from previous incidents, and the machine room has a portable heater near the controller. The building manager wants the mechanic to 'jumper the gate switch for the weekend' because a charity event is booked. The mechanic has a meter, laptop, and the fault log, but no spare travelling cable on the truck. The car is currently at the lobby with its doors open.
1. Outline a safe diagnostic sequence that respects the safety chain and identifies whether the fault is in the door circuit, travelling cable, or another switch. Explain why each step is ordered as it is.
Read the worked answer
Work from the safest, least invasive evidence outward. First, do not bypass anything. Secure the car, place it at a floor, and lock out the main disconnect before touching the safety chain. Download the fault log and correlate the 'safety chain open' events with floor, time of day, and temperature. A hot-afternoon pattern suggests thermal expansion at a connection, and the fourth-floor correlation suggests a specific travelling-cable flex point or a door-lock contact. Next, inspect the travelling cable at its supports and at the fourth-floor bend for broken strands, chafing, or a repair that has stiffened. Then, with the controller powered and the car stationary, use a meter to measure voltage drop across sections of the safety chain, and perform a controlled wiggle test on suspect harnesses. Compare door-lock and gate-switch contacts for pitting or loose terminals. The order matters because the fault log narrows the circuit before any live testing, and live testing is only done with the car stopped and guarded.
2. Why is the request to jumper the gate switch unacceptable, and what are the immediate alternatives?
Read the worked answer
Jumpering the gate switch is never an acceptable temporary repair. The gate switch is part of the door interlock logic that prevents the car from moving with a door open; bypassing it defeats a primary passenger protection and is an offence under Ontario's elevating devices regime. It also destroys the evidence: the intermittent fault will disappear and the next person will assume the car is healthy. The immediate alternatives are to keep the car out of service, tell the building manager in writing why, and arrange a qualified repair - replace the suspect travelling cable section or the door-lock contact, not the whole system if testing isolates a smaller cause. If the charity event needs access, the owner can use stairs or another elevator. The mechanic should notify the contractor and, if the owner pressures for a bypass, the TSSA inspector. Document the refusal.
3. What evidence should be captured, and what temporary measures, if any, are legitimate?
Read the worked answer
Capture the fault log before clearing it; record timestamps, floor, direction, load, and ambient temperature. Photograph the travelling cable repairs and any chafed or discoloured terminals. Record voltage-drop readings and the results of the wiggle test, including which circuit section changed. If a temporary repair is legitimate, it is a like-for-like replacement of a failed component - for example, a damaged door-lock contact or a cable support - followed by a full safety-circuit test at every floor, not a bypass. Any splice in a travelling cable should be treated as a permanent repair only if it is an approved method and is documented. After repair, run the car through all floors, test the door interlock and gate switch, and monitor for a week. Give the owner a written report that the root cause was found, not just that the fault 'reset.'