Doubts in ground testing that make electrical engineers pretty confused

Can I use an insulation tester to do the same test?

No. This is a common error. Field operators are often issued a Megger instrument from stores, without its being checked to determine whether it’s an insulation or ground tester. Insulation testers are designed to measure at the opposite end of the resistance spectrum from a ground tester.

However, a continuity test can only make an arbitrary measurement between an installed electrode and a reference ground, which is assumed to have negligible resistance. This does not afford a reliable measurement of the resistance the earth offers to a ground fault current.

Even this arbitrary measurement may not be reliable, since a dc continuity test can be influenced by soil transients, the electrical noise that is generated by utility ground currents trying to get back to the transformer, as well as other sources.

Test Equipment Megger 1000V Insulation and Continuity Tester