Kewtech KT66DL SPD testing

[Gavin John Hyde]

I bought the new Kewtech MFT - I wasn't expecting it until July. It arrived today so getting to grips with it. Not too different from the kt63 plus woth display. I have the kt64dl too.
It has a function for SPD testing.
Im not quite sure what it tells you though?
Its called SPD varistor test ....
Anybody able to offer advice or insight on what it tells you. Where would it be best used etc etc.. wondering if the spd guru (kirsty??) Might be able to help
There is no place on the test cert for it so wondering if a novelty?


Otherwise quite happy with the MFT. It has a good Anti trip loop test with reference for max zs values etc.. has memory function and optical adaptor fpr connecting to computer.
For myself the ev charging functions for different rcds was main reason as only a few mfts can test type b or do the dc current test.
Only paid £950 + vat as i strong armed rexel into ordering it for me.

 

[pc1966]

The SPD test is just a tarting up of the usual IR test where it tries to put out 500V (or 1kV) at up to a couple of mA, and shows a low IR if current flows. That is often seen as a fault (low IR) but if you know it is down to the SPD then the voltage at which you get a mA or two flowing is a measure of the varistor characteristics. That is the reason to check at 250V if you suspect a SPD is present, as then it won't conduct (must designed to clear at least the 253V * sqrt(2) = 358V peak of a mains sine-wave) and you ought to see many Mohm as a result.

Typically varistor (MOV) have a spec for a mA or so for production characterisation as it is easy to test, and then a clamping value tens or hundreds or so volts above that at 100s of A or several kA region which gives you the peak let-through voltage when subject to a surge (plus the impact of wiring inductance, etc).

The Wikipedia page has a typical current-volt plot:

Varistor - Wikipedia

en.wikipedia.org