mex zs to high

[albi]

i must be missing some thing. a pir has picked up on a lighting ciruit type c 20amp bs60898 2.5singles with a 1.5mm earth the r1_+r2 reading is 0.80 ohmes the ze was 0.54 ohms so the maz earth loop was 1.34 ohms. the niceic book says for that mcb the max is 0.92 omhs so i have upgraded the cable to 6mm t&e to bring the reading down and also take in for volt drop as the installers did not but the r1+r2 reading has gone up not down it now reads 3.04 omhs so why is this it should be going down not up.

 

[Sintra]

Only explanation is a loose connection if you used same route for new cable.

Also seems a large cable and overcurrent device for a lighting circuit i take it it must be a commercial or industrial installation.

 

[albi]

yes in a factory out let 400w mbfu low bays pulling 19.35 amps longest run is about 37m

 

[Sintra]

My advice would be to test R1 + R2 at every point along the circuit untill you find a section that gives you a high resistance.

 

[albi]

cheers for that head has been in the shed trying to work it out will give it a go tomorow

 

[Sintra]

Let us know how you get on.

 

[albi]

just the ticket the boy had not give the screw a final nip (i say boy as he is my mate and a spark)

 

[Sintra]

Good job at least you got it sorted.