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roffe 24th October 2007 11:51 AM

PTC resistors for protection of small transformers
I am looking at certain transformers from Hahn (examples: ), and notice this:

"Primary protection by means of transformer hegt coils to IEC 127 standards or secondarily with PTC resistances".

I must admit that I am pretty new to PTC resistances.

Can someone who knows explain a bit on how to select the correct PTC resistor and implement transformer protection for a specific transformer (schematics or by explanation)?

MaKari 14th November 2007 09:19 AM

Please, check the link:

Anyway the primary fuse is the must in diy equipment.

fernando_g 15th November 2007 01:03 PM

I agree with MaKari. A primary fuse is mandatory protection.

The problem that I see with PTCs is that their trip point varies substantially with ambient temperature. Therefore, they should be seen as backup protection only, the fuse is always a must.

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