incorrect insulation resistance reading

[ambrad]

Hi all, be gentle.

I have been asked to renew a cu so did some testing before commiting myself to the job.

The board is fairly old with breakers and main switch. I was doing a ins resistance test on a radial that fed 4 sockets in the kitchen and a two way board in the garage. The cable at the board is 6mm and goes under the floor and reapears at the sockets and garage in 2.5mm. There appears to be a jb under the kitchen floor that is covered in expensive lino, glued down.

When i did my test i got a slow reading >999 for the line/neutral and line /earth but a reading of 0.00 for earth/neutral. I believe this is a short caused by touching cables in the jb i cant get to or damage to the cable with a screw or nail bridging the earth/neutral.

Have i read my meter correct and therefore my damage assumption is correct or is there something else that could be the problem.

My issue is i cant get to the jb to check it. Should i suggest a rewire of this circuit to allow me to fit hte new cu with working rcd,s.

Thanks for any help

 

[Octopus]

Hum. My guess is that rewiring the circuit will be messy so I'd talk the options through with the customer. Changing a CU with an issue as you outlins isn't a great idea!

 

[ambrad]

thanks murdoch

Do you think that my assumption of the problem was probably correct

 

[Octopus]

Probably, but without looking who knows. Have you tried your scheme's technical help line?

 

[topquark]

What size of OCPD is on the 6mm cable at the main CU? I'd be a little concerned at the cable size changing from 6mm->2.5mm without it being fused down (is it possible they've spured off the cooker circuit?). You may be lucky and find the earth/neutral fault at one of the sockets.

As Murdoch suggests discuss with the client and present the options.

 

[tony mc]

I aggree with topquark re the 6mm to 2.5 that needs sorting.

Not being funny but you did disconnect the neutral fron the neutral bar in the CU before doing the test!