The insulation resistance between the conductors of consumer mains and submains; and live and earthed parts of an electrical installation, or parts thereof, including consumer mains and submains, shall be no less than 1 MOhm.

For shorter cable runs, the insulation resistance should be significantly greater than 1 MOhm. On an average installation a reading in the 100's of MOhms would be expected.

Wiring rules 8.3.6.3 (a) & ( b)