Hey Paul
For insulation resistance readings between conductors or earth you should get 200MOhm's or higher, 0.5MOhms does comply altho this requires further investigation.
Make sure you do the tests on a disconected circuit or you will get false readings.
Quote:the reading i get is 500 m ohms on all the tests with thats testing 1 curcuit or all at the same time as this is new to me im not sure whether this is right or wrong
Correct testing is between any conductor and earth, 500MOhms is a normal reading, you
can test all circuits together but you may get a lower reading and this would require spliting up all the circuits and testing one by one to ensure they all have acceptable readings.