electricalforum.nz

I have checked an existing wiring which is tested loop impedance test result was not acceptable (4 connections point , last point was 2.15ohm and the other was ok 1.35ohm , 0.65ohm 1.04ohm). do you think reason long wiring cable or MEN connection.....or something else ?

the way to fix it is :-
first off check that all the terminations are secure as a loose connection will give a bad test, then :-

Change to a B type trip curve MCB
or
reduce the circuit breaker size, for example a 20A circuit breaker, reduce to 16A, you may need to go down 2 sizes
or
Upgrade the size of the wiring for the circuit

@electricians
How about providing some additional information about the circuit? What size cable is it? How long is the run? What is the circuit protective device? Mcb? RCD? Rating?
What type of circuit? Lighting? Socket outlets?

Looking at the results he got where 1.35 ohm was a pass and 2.15 was a fail, looking at table 8.1 it could be a 20A MCB - C Curve, 1.53 is the maximum loop, this increases to 1.92 for a 16A MCB.

My bet would be 2.5mm2 on a 20A MCB, but yes good to know some more details

C16 A RCBO and 2.5mm cable and ever 15-20metres located 4 boxes . anyone get any issue if there is no MEN connection?

I would be looking for a poor connection somewhere

All of the readings you provided are too high for a 20m run of 2.5

You should do some low-ohm resistance tests to find out where the problem is.

If you are doing a non-powered test using method 8.3.9.3 (a) I read Table 8.2 with a C breaker as only allowing 1.22 ohms.