# Can one use a current transformer of 1A for a 5A input [closed]

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?

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I'm afraid I don't understand, could you elaborate on this: what ratio does the transformer have, what current capability, what current application is it for? –  Vlad Sep 18 '12 at 15:25
Ratio is for example 20/1 or 400/1A. I have different CT's in my possesion. I don't care to much about the ratio's since I can manage the input of the signal, the only care I have is "are" the results calculated correctly when doing this or not.. –  FireFox Sep 18 '12 at 16:28
It is difficult to tell what is being asked here. –  Olin Lathrop Sep 18 '12 at 21:19

## closed as not a real question by Olin Lathrop, Brian Carlton, stevenvh, W5VO♦Oct 9 '12 at 1:53

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

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.

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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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But connecting a 1A rated secondary current wouldn't generate higher currents then 1A unless it's primary is going over it's maximum? + I don't understand how using the CT in this way could effect the transformer core? –  FireFox Sep 18 '12 at 16:29
In order to give a more detailed answer, I need to know more about the device you're using. What's the manufacturer and part number, or better yet, can you provide a link to its data sheet? –  Dave Tweed Sep 18 '12 at 17:40
Wouldn't the answer be generic for this question? –  FireFox Sep 18 '12 at 17:46
"What we have here is a failure to communicate." You're using words in unconventional ways, and I'm trying to discern your underlying meaning by getting you to use more words to describe exactly what you're trying to accomplish. For example, what exactly do you mean by "a 5A input circuit"? I could launch into a long dissertation about current transformers in general, but I'd prefer to answer your specific question. –  Dave Tweed Sep 18 '12 at 18:24
My appologies. I am stating that my CT would have a secondary current of 1A: for example 20A in the primary circuit would result in a current of 1A in the secondary circuit. Hence for the metering application the secondary circuit would be the input signal. I hope this makes it more clear. –  FireFox Sep 18 '12 at 18:50