[Question] IR test and earth leakage question

[Andrew_van_Zyl]

Inspected a friends house while I gain experience and am trying to understand something.

IR readings at 500V are between zero and under 1Mega Ohm on most of the circuits. ALL appliances and light bulbs removed, switches left on.

This is live conductor to earth. I tested everything at once and then circuit by circuit. I didn't think to combine Live and Neutral and then test to earth.

My Megger tester tested ok on a circuit I know is perfect.

Why is the EL not tripping?

Tested the buttons and with my elcb tester - trips faithfully at 25milliamperes.

House built in the 80's, good quality flat twin and earth in the ceiling, steel junction boxes - everything looks ok when I opened them. No ferrules used (those ceramic twist on things) but nothing obvious.

Questions:
1) Should the EL trip if IR readings show an issue?
2) How do I go about checking each circuit for a possible IR issue?
3) Rainy weather in JHB so I can expect water issues...but on ALL circuits?

Comments and advice welcome!

[Dylboy]

Intresting! But will try reply more later on what I think but at what Mohm or kohm or ohm will the ELU trip...

Like 1mOhm is the minimum but will that be enough to trip the ELU ?

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[Dylboy]

Same as, reading of let's say 3ohms between line and neutral... is that enough for a short circuit ?

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[Derlyn]

Inspected a friends house while I gain experience and am trying to understand something.

IR readings at 500V are between zero and under 1Mega Ohm on most of the circuits. ALL appliances and light bulbs removed, switches left on.

This is live conductor to earth. I tested everything at once and then circuit by circuit. I didn't think to combine Live and Neutral and then test to earth.

My Megger tester tested ok on a circuit I know is perfect.

Why is the EL not tripping?

Tested the buttons and with my elcb tester - trips faithfully at 25milliamperes.

House built in the 80's, good quality flat twin and earth in the ceiling, steel junction boxes - everything looks ok when I opened them. No ferrules used (those ceramic twist on things) but nothing obvious.

Questions:
1) Should the EL trip if IR readings show an issue?
2) How do I go about checking each circuit for a possible IR issue?
3) Rainy weather in JHB so I can expect water issues...but on ALL circuits?

Comments and advice welcome!

Finding faulty circuit

1. Disconnect live and neutral from load side of ELR.
2. Disconnect all neutrals from ELR neutral bar and separate them.
3. Make sure all circuit breakers are off.
4. Megger each live to earth.
5. Megger each neutral to earth.

You WILL find the culprit, that is if there is one.

Why is the earth leakage not tripping ?

By using simple ohms law you will see that any insulation resistance above 8k ( 8000 ohms ) will not cause the ELR to trip.

R = V/I ................ R = 240/0.03 = 8000 ohms. ( 8k )

[Andrew_van_Zyl]

Thank you Derlyn! Been tossing and turning all night.
Oh course! Makes perfect sense. Resistance HAS to be low (or under 8000 ohms) to trip.
High resistance won't trip as the milliamperes fall below the sensitivity of the ELCB.

Low resistance = dead short or a very good connection between conductors or between conductors and earth - depends what you're testing.

Ok my mojo is recharged and I am ready to go back and test as you suggested!

[Andrew_van_Zyl]

4 of the 16 Circuits still have issues. Mrs homeowner is in bed with the flu so can't check that circuit. Other circuits had loose connections in the socket outlets (these I ferruled and created a spur).
Oh yes...and a light INSIDE the chimney the homeowner forgot to tell me stopped working years ago - dead short.
I'm 2 days into this fault finding - I am determined to find the last ones.

Then I used a longer screw in a socket outlet and drove it into the conduit, shorting the circuit when I switched on later. 2 Hours later to find THE socket outlet responsible.

STEEP learning curve! But loving it!