MI Elevator Mechanic flashcards
MI Elevator Mechanic · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Governor tripping speed range
- Car governor tripping speed is set between 115% and 140% of rated speed, and must not exceed the A17.1 table value for that rated speed. Verify with a tachometer during annual testing.
- Rope safety factor
- A17.1 requires at least 12 for traction elevators above 50 ft/min and at least 16 for drum machines. The factor is the rope breaking strength divided by the maximum static load.
- Traction ratio formula
- Traction ratio equals total load on the sheave divided by the lesser rope tension. A 1:1 roping gives 1, 2:1 gives 2, and higher ratios reduce rope load while doubling rope travel.
- Synchronous speed formula
- Synchronous speed in rpm equals 120 times frequency in hertz divided by the number of poles. A 4-pole motor on 60 Hz has a synchronous speed of 1800 rpm.
- Percent slip calculation
- Percent slip equals synchronous speed minus measured speed, divided by synchronous speed, times 100. NEMA Design B motors typically run 2 to 4 percent slip at rated load.
- Hydraulic relief valve setting
- The relief valve must open at no more than 150% of full-load pressure. Test with the car at rest and loaded, and record the opening pressure on the maintenance record.
- Hydraulic speed relation
- Rated speed equals pump flow divided by plunger area. Doubling plunger area halves speed at the same flow, which is why cylinder diameter and pump displacement must be matched.
- Oil buffer threshold
- Oil buffers are required for rated speeds above 200 ft/min; spring buffers are permitted below that. Buffer stroke must match the A17.1 table for the rated speed.
- Brake rated holding capacity
- The brake must hold 125% of rated load. It is spring-set and power-released, so loss of electrical or hydraulic power applies the brake, not releases it.
- Five-year safety test
- Every five years the safety device is tested at 125% of rated load, along with a full-load test of the machine and brake. Record stopping distance and even safety engagement.
- Escalator maximum rise
- A single escalator unit may not exceed 60 ft (18.3 m) of rise. Speed is limited to 125 ft/min above 20 ft rise and 100 ft/min at or below 20 ft.
- Car minimum clear height
- Clear inside car height must be at least 7 ft (2.13 m). Car doors must be at least 6 ft 8 in (2.03 m) high with an unobstructed clear opening.
- Car emergency lighting duration
- Emergency lighting must provide at least 5 ft-candles at the car threshold for 4 hours. Normal car lighting must give at least 2 ft-candles at the floor with doors closed.
- Machine room door requirements
- Access doors must be self-closing, self-locking, open outward, and measure at least 30 in wide by 6 ft 8 in high. The room must be kept locked against unauthorized entry.
- Three-phase power formula
- Real power in watts equals 1.732 times line voltage times line current times power factor. Use this to size feeders and confirm motor branch-circuit capacity.
- Across-the-line inrush current
- Direct-on-line starting draws roughly six times nameplate full-load current. Wye-delta and reduced-voltage starters cut inrush but also reduce starting torque.
- NEMA AC-3 contactor rating
- AC-3 is the utilization category for squirrel-cage motor starting. Size contactors by horsepower rating and category, not by amp rating alone.
- VFD shielded cable grounding
- Shielded motor cable must be grounded at the drive end. Long unshielded runs cause reflected-wave overvoltage at motor terminals and damage insulation.
- Suspension rope minimum count
- Traction elevators require at least three suspension ropes, each independently terminated and equalized. Fiber-core ropes are not permitted for traction suspension.
- Sheave-to-rope diameter ratio
- Traction sheave diameter must be at least 40 times the rope diameter. Smaller ratios accelerate fatigue and require more frequent rope inspection and replacement.
- Counterweight balance point
- The counterweight equals car weight plus roughly 40 to 50 percent of rated load. This balances tension so the machine sees near-equal loads up and down.
- Instantaneous safety speed limit
- Instantaneous safeties are permitted only below about 200 ft/min for cars. Above that, type A or type B progressive safeties are required to limit deceleration.
- Governor rope minimum diameter
- The governor rope must be at least 1/4 in (6.4 mm) in diameter and properly tensioned so the governor trips before the car reaches the pit buffers.
- Final limit switch function
- Final limit switches are independent of normal limits and must open the power circuit before the car or counterweight reaches the buffer, preventing overtravel damage.
- Annual hydraulic test items
- Annual tests include the safety device with rated load, governor tripping speed, buffer test, brake test, and relief valve test on hydraulic units. Record all measured values.
- Escalator skirt clearance
- Step-to-skirt clearance must not exceed 3/16 in per side. Also check comb teeth engagement, handrail speed, and stop switch operation during inspection.
- Michigan licensing authority
- The Elevator Safety Board within LARA issues mechanic and contractor licenses and adopts ASME A17.1 and A17.3 by reference. Unlicensed work carries civil penalties.
- Michigan certificate of operation
- A certificate of operation must be posted in the car or machine room and renewed annually after inspection. The owner arranges and pays for periodic inspections.
- Michigan permit requirement
- A permit is required before installing or altering an elevator. The contractor submits plans, and the state inspects before the unit is placed in service.
- OSHA fall protection trigger
- General industry requires fall protection at 4 ft; construction at 6 ft. Hoistway work uses a full-body harness with a rated anchor of 5,000 lb per worker.
- Sling angle capacity reduction
- Sling capacity drops with angle from horizontal. At 30 degrees, capacity is 50 percent of the vertical rating; at 60 degrees it is about 87 percent.
- Lockout/tagout requirement
- Under 29 CFR 1910.147, isolate all energy sources, verify zero energy, and apply personal locks before working in the hoistway or machine room.