Hi. I have Metrel MI 3152 multifunctional tester and in the Line, Z auto menu there is a setting for Zlim(Z (LPE),Z (LN)) and it is fixed at 2.18 ohms can’t be adjusted. I’ve just done a job on a site and the prospective short circuit fault current is very low and really limits the length of and size of conductors we can use. And testing an existing circuit shows that there the 20A C-type breakers they have in now will take 13-14s to trip, where as a B would be .4 or less. This is a remote TT building from a TNCS supply with 100mA rcd, so fault protection is okay, quite a way from the supply. So I thought I’d use my tester just to drop back from C to B, rather than look at the graphs in the Regs, to see if reducing the type from C to B would satisfy but it seems that the 2.18 ohm limit is a significant factor in the tester, its fixed in red and won’t let me circumvent and conciquentky states fail even though tegs say fine. Am I being thick here what am I missing? My thoughts were looking at the current characteristics graphs in the regs I could reduce from C to B then swap the C the RCBOs for Bs because they’re not using inductive loads on most of the affected circuits and the B type curve would work with the 104A PSC I have on the end of one if the circuits / 150A in the board. But the tester says fail! Because of the 2.18 ohm.
Any thoughts please?
Cheers
John
Any thoughts please?
Cheers
John