Insulation Resistance test

sparko · Nov 25, 2010

Hi guys, I'm currently studying level 3 c&g 2330, and have my testing exam coming up very shortly. I was wondering if there was more than 1 way to test insulation resistance, and if so which is the most common because 1 of the lecturers told me: with the main isolator locked off, with the tester set to 500v,all 500v harmed disconnected, and all mcb's and switches on, at the bottom of the main isolator switch in the c.u probe between Line & neutral, then Line at same point to main earth bar, and finally Neutral at bottom of main isolator to main earth bar. Then when I was practicing testing at college the other day a different lecturer said I should: with all mcb's & switches on, probe between any mcb and main earth bar, any mcb and main neutral bar(terminal) and between earth and neutral bars. Now I am confused, can anybody shed some light please? One last point, if testing ins. res with tester set to 200 mega ohms and a reading that says (overange 1) what do I write in the test box, simply 200 mega ohms or is it >200 mega ohms.

markysparky · Nov 25, 2010

Both right (in a way) 1st teacher is more closer to GN3 (starts page 37) 2nd teacher is testing each circuit individually.(Generally done if IR is low (parallel resistances) (Bit more time consuming) If you have full control of the installation then 1st teacher method is best and quickest. Tests whole installation greater than 1mohm, job done. If its more than 200m ohm then put >200m ohm in the box.

Don't forget to flick the switching on any two way and or intermediate lighting (page 39 GN3)

Read GN3 from page 37, its self explanitary

Markysparky

IQ Electrical · Nov 26, 2010

sparko said:
Hi guys, I'm currently studying level 3 c&g 2330, and have my testing exam coming up very shortly. I was wondering if there was more than 1 way to test insulation resistance, and if so which is the most common because 1 of the lecturers told me: with the main isolator locked off, with the tester set to 500v,all 500v harmed disconnected, and all mcb's and switches on, at the bottom of the main isolator switch in the c.u probe between Line & neutral, then Line at same point to main earth bar, and finally Neutral at bottom of main isolator to main earth bar. Then when I was practicing testing at college the other day a different lecturer said I should: with all mcb's & switches on, probe between any mcb and main earth bar, any mcb and main neutral bar(terminal) and between earth and neutral bars. Now I am confused, can anybody shed some light please? One last point, if testing ins. res with tester set to 200 mega ohms and a reading that says (overange 1) what do I write in the test box, simply 200 mega ohms or is it >200 mega ohms.

The first method is what we refer to as a global IR test, this is a great time saver but only really practical on simple installations.

If the reading (s) on the global IR test are unsatisfactory then the installation should be IR tested circuit by circuit (as per lecturer 2) to identify where the low IR reading is coming from.