Standard Zs versus no-trip Zs

springcrocus · Jan 23, 2011

I have to post this in here for a reason...

Standard Zs versus no-trip Zs

Most sparks are aware that a no-trip Zs test will normally return a higher value than a standard Zs test, sometimes giving readings close to or over the tabulated values for the CPD. So, in true Apache style (thoroughly enjoyed the crimps v wagos), I thought I would conduct a little experiment to see how great these differences were.

I had originally planned to just present a table of results but then thought: What the heck, write it in

Manator · Jan 23, 2011

He has his uses that canoeboy, good post and some very good advice from canoeboy in a previous post, as he said nice table.

NozSpark · Jan 23, 2011

Very good post..

TBH I always calculate the Zs on RCD protected circuits as I find that the NO TRIP Zs readings high... just like you've confirmed

PC Electrics · Jan 23, 2011

I think you should get your meter checked.

I have an MFT1552 and whenever I do a CU change and carry out (Hi) Zs tests before the change, i also do no-trip tests at the same time to compare the results directly. Except on a few occasions when I've subsequently found faults in the circuits the two Zs readings have never varied by more than 0.05, which I believe to be perfectly acceptable.

springcrocus · Jan 23, 2011

I think you should get your meter checked.I have an MFT1552 and whenever I do a CU change and carry out (Hi) Zs tests before the change, i also do no-trip tests at the same time to compare the results directly. Except on a few occasions when I've subsequently found faults in the circuits the two Zs readings have never varied by more than 0.05, which I believe to be perfectly acceptable.

It may vary on a meter-to-meter basis, but whenever I've spoken to other sparks in the local wholesalers (it's a right Darby and Joan club here), the general consensus is that no-trip Zs results are always on the high side and considered unreliable.

Anyway, I have already arranged with the homeowner to go back next Wednesday and do some more tests. A mate of mine is bringing his Fluke 1652 and I'm borrowing a Metrel MI 2087. We are going to do the same standard and no-trip tests with both meters and I will post the results up here on Thursday. Lets hope that the changes that Admin is making to the forum tonight do not stop me posting the tabulated data.