Mad IR readings when looking at a CU change

JulianC · Mar 17, 2010

Here's one that caused a bit of head scratching today. Customer calls asking for a quote to do a board change 'cos they are selling their house and reckon the old Bakelite Wylex rewireable fuseboard might put potential buyers off. So I strolled over with my tester and tools this afternoon (I can see their house from mine - seemed silly to drive) to have a look. The old board belongs in a museum - it looks lovely I reckon. Anyhoo, power off, whipped the cover off and did my usual 250v IR test across N & E bars. It's down to 0.02 Meg. Hmmmm. What follows is plenty of head scratching as neutrals are systematically disconnected and the tests repeated. Disconnected downstairs ring N, reading up to 99.9 Meg. Check downstairs ring in isolation, 99.9 Meg. Put downstairs ring back in board and reading now at 1.15 Meg. Cock about a bit more and variously get readings between 0.02 and 1.5 Meg. Without doing anything. Megger seems to be working OK. I am talking to customer about the way forward when she mentions that they have a mouse!!! Could this be the cause of my mental IR readings or have I missed something? Does Bakelite become conductive in its old age?

Attempts to trap our rodent friend so far have apparently been unsuccessful. Do we just hope the little bugger electrocutes itself? Upshot is customer will probably leave the board as is, for the next occupant to worry about.

DurhamSparky · Mar 17, 2010

quailty!!! mice cause alsorts of crap!! i had one that chewed through the customers socket cable near DB!!

Jason Smith · Mar 17, 2010

Thats easy to answer. Every time you put 250 V up the mouses arse it jumped across onto a different wire, sometimes its tail still in contact with the other wire. When it finally got the message and got off you got your good readings. Untill you tested another wire, the one it was now sat on. It then jumped back onto the other wire, screwing up your readings again.

c.p.c · Mar 18, 2010

I would have been tempted to pass 1000v IR down the rings (with every plug top disconnected / all precautions taken off course) and fried its fur off.

you then could have charged for exterminating it

,and don`t forget to change your name to Renta - kill - kid on the top of your invoice.