ASME A17.1 minimum rope safety factor by speed

ASME A17.1 Table 2.20.3 establishes the minimum suspension-rope factor of safety from rope speed and whether the elevator is passenger or freight. Two items are important when using the table: use rope speed rather than car speed, and interpolate between the listed speeds where required.

Use rope speed, not car speed

The lookup takes the speed of the suspension member: car speed multiplied by the roping ratio. For 2:1 roping, rope speed is twice car speed, so a 350 ft/min elevator has a rope speed of 700 ft/min and the minimum factor of safety is taken from the 700 ft/min row. Using car speed on a 2:1 elevator gives the wrong minimum factor of safety.

Minimum factor of safety

ASME A17.1 Table 2.20.3 — minimum suspension-rope factor of safety
Rope speed ft/min	Rope speed m/s	Passenger min. Sf	Freight min. Sf
50	0.25	7.60	6.65
75	0.38	7.75	6.85
100	0.51	7.97	7.00
125	0.64	8.10	7.15
150	0.76	8.25	7.30
175	0.89	8.40	7.45
200	1.02	8.60	7.65
225	1.14	8.75	7.75
250	1.27	8.90	7.90
300	1.52	9.20	8.20
350	1.78	9.50	8.45
400	2.03	9.75	8.70
450	2.29	10.00	8.90
500	2.54	10.25	9.15
550	2.79	10.45	9.30
600	3.05	10.70	9.50
650	3.30	10.85	9.65
700	3.56	11.00	9.80
750	3.81	11.15	9.90
800	4.06	11.25	10.00
850	4.32	11.35	10.10
900	4.57	11.45	10.15
950	4.83	11.50	10.20
1,000	5.08	11.55	10.30
1,050	5.33	11.65	10.35
1,100	5.59	11.70	10.40
1,150	5.84	11.75	10.45
1,200	6.10	11.80	10.50
1,250	6.35	11.80	10.50
1,300	6.60	11.85	10.55
1,350	6.86	11.85	10.55
1,400	7.11	11.90	10.55

Between the rows, and past the ends

Between rows the value is interpolated linearly. A rope speed of 375 ft/min falls between 350 (9.50) and 400 (9.75), giving 9.625 for passenger duty.
Below the first row the first value holds: anything at or under 50 ft/min takes 7.60 passenger, 6.65 freight.
Above the last row the last value holds: 11.90 passenger, 10.55 freight.

Ropes below 9.5 mm

For suspension members 8 mm or larger but less than 9.5 mm, A17.1 requires a minimum factor of safety of 12 unless broken-suspension-member detection is provided. Where applicable, this requirement governs if it is greater than the value obtained from Table 2.20.3.

What the factor is compared against

The actual factor of safety is f = (S × N) / W — the rope breaking strength times the number of suspension runs, over the maximum static load carried by the ropes. W includes the weight of the suspension ropes themselves, which is why a hand calculation that omits the rope term comes out a few percent optimistic on a tall rise.

Values are reproduced for reference from ASME A17.1-2022 Table 2.20.3 and are the figures this calculator uses. The published standard is the authority — check against your own edition, since requirements change between editions and jurisdictions may amend them.

Check a job against this table