Dem ist leider so. Danke für den Hinweis!
Hier ein Auszug aus dem Post:
DC resistance of the CT
Other than the current clamps with 50A and 120A, the 3CT63 measures 14,5Ω at its secondary terminals (50A/120A clamps show approximately 480Ω).
Looking into the guts
After opening, three 22Ω resistors appear:
These resistors are in parallel to the coils:
This forms a current divider: A certain part of the secondary current is effective for the ADC input. With Ohms law, this part is 0,64706, which leads to a transmission ratio of 1: 6471. This is confirmed by measurements with various configurations of CT types. Native transmission ratio of the CT is 1:1000, which could be confirmed by a measurement without an additional burden resistance.
Why a parallel resistance?
The reason is economically: To protect the current transformer from being destroyed by overvoltage in the case of no burden resistance, the 50A and 120A current clamps include TVS diodes, which are limiting the secondary voltage to some 5 volts:
But these TVS diodes are not as cheap as a simple resistor. Thus, it is cheaper to add a fixed additional burden resistance as to add TVS diodes. Trade-off is a lower transmission ratio.