# Insulation Resistance Test



## camilleri

Hello how are you?

I am Stephen Camilleri from Malta and I need some help.


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## camilleri

My problem is sometimes when I have a fault on the Neutral i get a bit confused in doing my tests. I learned that when making Insulation Resistance Test at the lighting part if you cannot take off the bulbs etc, you turn off the swithch and then make the test but by doing this the neutral is not disconnected from the bulb? 
(since the switch disconnects only the phase(live).

These type of problem arises to me when I have faults that are not continous and the RCD trips unevenly say 3 times a week.

Your help is greatly appreicated
Thanks 
Stephen


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## JohnR

Yes, if wired correctly, the neutral is normally still connected to the light bulb. If you are still getting the fault when the switch is off, remove the lightbulb and then test again. If the fault is gone, then the fault is on the line side of the lamps back to the switch. If the fault is still there, then the fault could be anywhere. It could be the fixture that is faulty, not just the building wiring.

I just re'read your post, what is the neutral faulting to? Earth/ Ground? or the phase conductor?


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## camilleri

*Problem with RCD falling*

First of all thanks for your help,

My problem is the RCD is not falling continously so sometimes I go to make my tests to avoid these trips. When I amke an insulation test I found the reading about 0.2 to .5 which I know the minimum should be 1M Ohm. In some cases the spotlights are wired with a transformer to turn AC into DC so how can I check if I cannot remove these transformers because they are in the gypsum suffit??

Another thing is that when I swithc on the Double Pole (Main switch before the RCD) sometimes the RCD trips does this mean that there is a fault in the Neutral??

When you have a two way switch I learned that you should do the insulation test twice in both ways. What results should i expect from this to be correst for ex on test infinity and the other test zero??

Thanks a lot for your help

Stephen


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## camilleri

*Insulation ResistanceTest*

Can anyone help me pls because I hadnt received any reply?


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## WarrenG

An RCD detects a leakage fault which could be caused by a number of reasons. 

Is there any reason why you are attempting to test the lighting circuit? Do you suspect that the lighting is the cause of the fault?

You need to take a look at the circuits that the RCD is protecting. Standard RCD's have a 30mA setting for the detection of earth faults, but from my experience can trtp out anywhere between 22-26mA when tested.

A leakage fault could be caused by a faulty electrical appliance that you have plugged into your sockets with a high earth leakage or by having a number of appliances all switched on at the same time with a cumulative high earth leakage. Another reason could include moisture on cooker elements.

It can sometimes be a bit tricky to pin point fautly electrical items without the use of an Earth Fault Clamp Meter, however when the RCD trips you could remove ALL the electrical appliances plugged in, re-energise the RCD and plug each appliance back in one at a time to see if it trips again. If it does you have likely found your faulty appliance.

Its better to have the system checked out correctly because intermittant faults can sometimes take a while to pin point. 

For example in the UK I have come across faults such as the RCD tripping when the motor on the fridge freezer has kicked in because the stat has dropped and the rise of earth leakage has pushed the RCD just above its thresh hold. 

An earth clamp meter could determine what appliances are leaking at what levels and a 'Ramp' test on your actual RCD will determine at what level your RCD trips out at.


For reference about IR tests, you should not be testing the circuits with any light bulbs in place, any neons connectioned, or any sensitive electronic equipment in circuit or you will damage them.

Hope this helps.


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## camilleri

Dear Mr Warren G,

first of all thanks a lot for your help.

I was testing the lighting circuits and not doing the way you described because with the MCBs all down the RCD still drops so I suspected the fault from the Neutral. Another thing which I taught from the Neutral because when I made my tests on the Neutral the lighting circuits of two rooms gave me .2 M Ohms with the megger which is bad no?

Is the Earth Fault Clamp meter used to detect faults on the Neutral and on lighting circuits and how is this used?

If you can have time your help is greatly appreicated?

Thanks a lot
Steve


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## camilleri

Can I ask where I can buy the Earth Fault Clamp Meter becuase I search on ebay and I didnt found or does it has another name?

Thanks
Steve


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## WarrenG

Stephen,

Please do not attempt to carry out anything that you are unsure of or do not understand anything. Simply, Electricity can kill.

If you do normally work with electrics in Malta then you could try the following, 

As you have said that the RCD still trips even with the MCB's down ....

Switch off all your mcb's (closed down so that no circuits are live) and leave just the RCD on, if the RCD then still trips, you will have a neutral to earth fault somewhere in the system. 

If the RCD holds out by itself, turn on each seperate mcb one at a time until one causes the RCD to trip. That will probably be your faulty circuit.

If you think you have a neutral to earth fault, with the system completely switched off (de-energised), test for continuity between each of your circuit neutrals and earths seperately. You will need to disconnect them from the bars.

Again if you find that you have a connection between neutral to earth on a particular circuit this should identify it as the circuit thats causing the imbalance in the sytem.

Once you have found your faulty circuit, you will then need to pin point where exactly the fault in the circuit lies.

If it does turn out to be that your lighting circuit is faulty, you may find that it is one of your transformers that has broken down or what happens quite frequently here is a spot light has melted a cable in the ceiling?

Again, please do not attempt anything that you are not sure of to be safe.

Hope this helps?


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## camilleri

Dear Mr WarrenG

thanks a lot for your help,

I asked about that meter becuase I thought it was a meter that detects an Earth Fault.

So when I make a continuity test as you told me between the Neutrals and Earth at the bus bars and I find a circuit which makes continuity that is the faulty circuit I understood well??

When you have a tow way switch and you make an insulation resistance test twice (that what i always learned) what shouldbe the expected results the same reading?

Sometimes when turn on the RCD with the MCBs all on the RCD doesnt hold and when you switch off the MCBs and turn one after each other it holds what does this indicate?? (the installation is not overloaded to let you more in the picture)

Thanks a lot for help
Stephen


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## camilleri

Any answer for my previous question? Thanks


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