insulation bad readings

[flyboy]

can anyone help. when doing a ir test on ring cct i get a reaing n/l > 299 n/e >299 but l/e 148 this is on new wiring and same problem on three different ccts lighting cct 64 meg ohms nothing is plugged in anywhere all appliancies disconnected. though maybe a bit of bad cable but this is on 3 ccts seems a bit strange. have tested each indivdiual cable and they test ok but when put back together bad reading again. would appreciate any help. thanks dave

 

[telectrix]

they're not bad readings. just enter them on cert. as read. then move on.

 

[richy3333]

As Tel says, the readings are well within the guidelines set out by BS 7671?

Why would you think you have a 'bit of bad cable' on a newly installed circuit? Was it second hand Polish cable or something?

 

[telectrix]

if he's used prysmian cable, he's probably had to use a hilmor to bend it when cold. bloody awful stuff.

 

[Knobhead]

Just out of interest I did the old calculation of maximum leakage not being greater than 1/10,000[SUP]th[/SUP] of circuit FLC I was taught as an apprentice. That’s even more generous. For lighting on a 6A MCB it works out to 383K Ώ. For a RFC it’s 71K Ώ.
Remember I was playing about with VIR’s then.

The calculation is now used mainly for motors and PILC cables.
As I said I just did it out of interest.

 

[cobrauk]

what meter you using most of our meters read >200 as max

 

[richy3333]

what meter you using most of our meters read >200 as max

The Megger 1700 series go up to 999M ohms

 

[Engineer54]

So 148 million ohms means that you have a problem or a bad bit of cable?? Jesus get real!!

 

[markc123]

With anything over 1meg deemed satisfactory, 2meg warranting further investigation....i would say that 148 is a bloody good reading, mark it off and move on to the next test - i wouldn't even bat an eyelid.

 

[Octopus]

Thats why I love Metrel, on the auto function which tests L-N, L-E and N-E in one press of the button its max reading is >30

 

[londonlec]

Thats why I love Metrel, on the auto function which tests L-N, L-E and N-E in one press of the button its max reading is >30

Thats a good time saver, I bloody hate keep swapping the crocs over on my Megger

 

[markc123]

On single phase, I just link out the live bar feeding the breakers and protective device(s) at the bottom with the earth using abit of wire and croc-clips, then take the insulation reading between earth and neutral and if its over 2meg then it complys, if it isn't then test individually....and to be fair if it was a new install and it was anything as low as 2 i would rip it out and ------- the apprentice ha. Obviouslly do the test twice if theres 2 neutral's