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2–17
2.10.3 – Overload Current Profile and Duty Cycle AC-53a
IEC 60947-4-2 Motor Utilization Category: AC-53a (not operating in bypass mode)
IEC Index Ratings for standard operation are comprised of Rated Operational Current (I
e
),
Utilization Category AC-53a, Overload Current Profile (X-T
x
), and Duty Cycle (F-S).
To calculate times for a lower value of current, divide the square of the next highest given current
multiplied by its given time by the square of the required current.
For example:
• To find the time T
x
for X = 2.5 x I
e
, then Tx = (3
2
x 35) / (2.5)
2
= 50 seconds.
Index Rating Example – Standard Operation
(AC-53a Utilization Category per IEC 60947-4-2)
SR44 Index Ratings (for AC-53a) *
Soft Starter
Model Number
I
e
(A)
Standard Operation
UC X-T
x
F-S
SR44-9 to SR44-105 9 to 105
AC-53a
AC-53a
5-4
3-35
99-10
99-10
SR44-146 to SR44-202
146 to 202
AC-53a
AC-53a
4-6
3-35
99-10
99-10
SR44-242 to SR44-370 242 to 370
AC-53a
AC-53a
4-6
3-35
60-3
60-3
* Index ratings AC-53a and AC-53b are specified by IEC standard # 60947-4-2
AC-53a Overload Current Profiles (applicable to specified Soft Starter models)
Soft Starter
Model
X
Overload Current
(multiple of I
e
)
T
x
Duration of
Overload
(seconds)
F
Ratio of On-load
Period to Total
Load (%)
S
Number of
Operating Cycles
per Hour
SR44-9
to SR44-105
3 35 99 10
5 4 99 10
SR44-146
to SR44-202
3 35 99 10
4 6 99 10
SR44-242
to SR44-370
3 35 60 3
4 6 60 3
9 to 105 - AC-53a: 3-35; 99-10
Duty Cycle (F-S)
99-10 = 99% on-load factor - 10 cycles/hr
Overload Current Profile (X-T
x
)
3-35 = 3 times rated current (I
e
) for 35s
Utilization Category
AC-53a = controller semiconductors provide squirrel-cage motor Start, Run, and Stop control
Rated Operational Current (I
e
)
9 to 105 = controllers with Rated Operational Currents from 9A to 105A
For a 99% on-load factor
and 10 standard operating
cycles per hour,
the unit can accommodate
(3)x(I
e
) for 35 seconds
Chapter 2: Electrical Installation
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019