low IR readings

[brs73]

morning all
i've had some circuits recently where it was impossible to unplug everything so i done an insulation resistance test between live and neutral twisted together and earth at 250v.a lot of circuits were reading 0.00ohms or very low.
what types of equipment would cause this.
i also had the same readings on lighting circuits where i couldn't remove all lamps/transformers?

 

[Eggster71]

Things like ballasts in floury lights etc can cause this, fridge compressors and motors for example have a massive winding inside an earthed metal cage which will often give a low reading.
Torroidal transformers can do this too, in lighting.
Also dodgy wiring does this!
Have you isolated the entire circuit from the board? If, you had a neutral and earth still in the board you'd get this reading, turn off the main switch to isolate the outgoing neutrals from earth and try again. If it comes up clear you may have a borrowed neutral somewhere?