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Section 10
9
CT current transformers
Current
transformers
Specific case of the motor starter
To measure motor starter current, you must choose a CT with primary current
Ip = Id/2 (Id = motor starting current).
Practical advice
Use a current transformer to measure a nominal current of 50 A.
To divide by 2 the nominal current of a transformer, you only need to pass the current
to be measured twice through this transformer.
50/5 A CT: Imax = 50 A
100/5 A CT, 2 cable openings: Imax = 50 A