CT1 and CT2

Do not confuse surge levels one and two (or three or four )with surge arrestor configurations one and two. 

Note I am not using Arabic or Roman numerals just yet deliberately - and there are also classes of insulation and ADS method 0, 0A 1 (earthed) and 2 (double insulated) to be confused by.

It would be much easier if for new concepts we did not insist on restarting the count from 1 or A but began instead at unique multiples of perhaps 500 or 23 or almost anything really. But we do not.. This leads to similar silliness as our B type RCBO with A type RCD performance.

Back to the chase...

There are 4 levels of over voltage 1,2,3,4  from the 13A plug out to the overhead line, although it is a bit arbitrary, as in some cases there is a direct connection

https://www.cui.com/blog/understanding-iec-overvoltage-categories

But there are also configurations of surge suppressor CT1 and CT2 that are as Andy described above.

Arguably either of these may reduce a level IV over voltage into a level II or III but that has little to do with the CT1 CT2 wiring configuration of it and is all about the breakdown voltage of the suppression elements and the inductance of the wiring to them.

Mike.

(we do seem to like making things deliberately awkward and then wonder why folk get confused.)

Do not confuse surge levels one and two (or three or four )with surge arrestor configurations one and two. 

Note I am not using Arabic or Roman numerals just yet deliberately - and there are also classes of insulation and ADS method 0, 0A 1 (earthed) and 2 (double insulated) to be confused by.

It would be much easier if for new concepts we did not insist on restarting the count from 1 or A but began instead at unique multiples of perhaps 500 or 23 or almost anything really. But we do not.. This leads to similar silliness as our B type RCBO with A type RCD performance.

Back to the chase...

There are 4 levels of over voltage 1,2,3,4  from the 13A plug out to the overhead line, although it is a bit arbitrary, as in some cases there is a direct connection

https://www.cui.com/blog/understanding-iec-overvoltage-categories

But there are also configurations of surge suppressor CT1 and CT2 that are as Andy described above.

Arguably either of these may reduce a level IV over voltage into a level II or III but that has little to do with the CT1 CT2 wiring configuration of it and is all about the breakdown voltage of the suppression elements and the inductance of the wiring to them.

Mike.

(we do seem to like making things deliberately awkward and then wonder why folk get confused.)