Is it possible to use a current transformer that is rated secundary 1A for a 5A input circuit taking into account the scale (hence multiply the output *5) or would this cause problems?
closed as not a real question by Olin Lathrop, Brian Carlton, stevenvh, W5VO♦ Oct 9 '12 at 1:53
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Current transformer 100 to 1, for example.line current 20 amp, current in secondary coil of current transformer will be 0.2 amp. For transformer 100 to 5 ,line current 20 amp, current in secondary coil will be 1 amp. 5 amp input circuit will handle 0.2 amp without any problem, but it supposed to be graduated according to the high range of measurement -- highest possible line current. As in your question, you can use multiplier of 5 in case you replace current transformer with the same measurement range e.g. (100 to 5) by (100 to 1). Other way you will overload input circuit.
If I understand your question correctly in the context of your followup comments, you have a circuit that's designed to measure current up to 5A, and you want to know what would happen if you connect it to a 20:1 (or maybe a 400:1) current transformer.
The 20:1 transformer would give the circuit an effective measurement range of up to 100A. If you're really only measuring currents up to 20A, then you'll only be using 1/5 of the range of the measurement circuit. If the circuit is digital, you'll effectively lose about two bits of resolution.
If you really want to measure currents up to 100A, then you need to be sure that the secondary of the current transformer can handle 5A — that it has sufficiently heavy wire and that the core isn't going to saturate.
The 400:1 transformer would allow you to measure currents up to 2000A.
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