Interesting using those meters..like to see tests like that instead of just testing voltage output.......maybe you will show us more tests in the future...like those meters you have dave.what is the insulation setting all about?
I had one of those small Flukes a while back, until someone smashed the screen on it, only binned it a few weeks ago, it was nearly new. Its a good cheap Fluke. Autoranging is one of the main plus points that most Flukes have, so you do not have to mess about guessing the range of readings that you think you need to measure.
Insulation test is a check to see if there is any leakage of current to earth, mainly used in domestic installations, known in the trade as Megger check. It sends a high voltage (between 250 and 1000v) down the wire to be checked and earth, and any "leaking" current can be detected and read displayed on the screen as a resistive measurement to earth - or how good the insulation is as a resistor against current flow to earth.
Good for checking motors, heating elements and also mandatory tests in new building and public buildings where installation certificates have to be issued. All newly installed circuits should now be tested by an authorised and certificated electrician.
In car circuits, the Insulation test would not be advised, as it would probably blow any electronics that are in the car, especially being negative earthed, but could be used for example to test the insulation on a wiper motor or maybe a starter motor once disconnected from the car.
A brief diagram showing how the test works.
This motor has two windings, the picture shows the two windings being tested between each other first, then one lead is connected to the metal case of the motor and one winding is then tested for insulation resistance against the metal case. If the winding was short circuited to the case, the test would show this up and tell you that the motor winding needed to be repaired. Ideally a value of 200Mohm resistance or more is what is good, anything lower than 150Mohm (150 mega-ohm or 150 000 000 ohms) is where you may suspect ingress of moisture or foreign objects that are allowing a bit of current to "leak" . Anything under 2 Mohm is where you really will be thinking of getting the motor repaired or replaced. I have seen circuits as low as 0.5Mohm still up and running, but this would be on a supply without any earth leakage protection such as RCD or RCBO like in your consumer unit at home.
On a 12 volt circuit as in your car, you could probably get away with leakage as low as 50Kohm in your isulation as lower voltages will not tend to jump across insulation faults the same as higher voltages such as in your home.
Sundance