IR test prior to CU change. Am I being over cautious?

[JulianC]

Afternoon all.

Just been for an initial look at a potential CU change. Customer has an old Wylex fuseboard, installed when his property was rewired 20 years ago. I did a 250v IR test across the N and E bars and got a reading of 3.4Mohms. Each N tested individually to the E bar resulted in similarly lowish values. I know we are allowed a minimum of 1M, with investigations to be carried out at 2M but surely IR on a healthy installation should be considerably more than this, even at 20years old? Presumably, the readings could well deteriorate further when 500v is whacked up the cables. I am not comfortable in changing the CU without further investigations. Am I being over-cautious? What would you do?

Ta.

 

[Mr Mark Sparks]

i doubt there will be to many probs its probably just one circ bringing the readings down when you test at the end i suspect the readings will be ok

dont lose a job over it
you will come across loads of jobs like this and cant turn them all down

 

[V]

i changed one like that with the bs3036's

6 way to a 17 ed board

just crack on mate

 

[Jason Smith]

loads of ways anyway of improving IR results mate, because there are loads of things that can effect it, I had to join in to a conservatory circuit the other day because of a concrete floor, it was reading 8 MO, dropped the face plates off all night and they dried out enough to bring up to 150 MO- entirely acceptable.
Dont forget AC current will over years, make connections loose, just a nip up in each back box or point will often incredibly inmprove results, so will clearing the obligatory five hundred woodlice from the odd socket. Cobwebs dont help either.Notwithstanding a genuine fault.