Appendix D: Sizing an SR55 Soft Starter
Page D–5Stellar
®
SR55 Series Soft Starter User Manual – 1st Ed, Rev F – 09/18/2019
INcReAsed sTARTs peR houR – deRATING
If more than the standard number of starts/hour is required, the SR55 must be derated. To
derate for more starts/hour, the motor full load current must be less than the SR55 current.
The relationship between the SR55 deration and the starts/hour is given below in Figure 2 and
the two examples that follow. This assumes that the SR55 is still operating at the same duty
(F) as given in Figure 1.
Figure 2: SR55 Starts/Hour Deration
Deration Curve Starts/Hour Deration Factor
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
10 15 20 25 30 35 40
Deration Factor
[ Motor Full Load Current / SR55 Current ]
Starts / Hour
10 0.83
15 0.73
20 0.66
25 0.61
30 0.56
35 0.53
40 0.50
Deration Factor = (138 - (24·ln(starts/hr))) / 100
[where ln(starts/hr) is the natural log of the # of starts/hour]
Example: Deration Factor for 10 starts/hr = (138 - (24·ln(10))) / 100 = 0.83
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