Poor ir on when connected to mcb

[Les Macaulay]

Try testing between the dead outgoing terminal of the MCB with no wires connected and see what the reading is.
Les

 

[davesparks]

why would you code anything? The readings in your example above are way above what is ok

I would say they are not ok for a test applied between incoming and outgoing terminals of an MCB in the open position, the reading should be far higher and it is a sign that the MCB has become damaged, most likely through moisture ingress in this situation.

 

[Midwest]

I tested all at 250v getting about 1M with n-l connected in mcb switched off and when tested at 500v I got about 0.05 yet when connected in a terminal block out of mcb I was getting 30M plus

As others have said, perhaps the mcb's have become faulty. Don't understand why your using the mcb's as a connector to do your IR tests, or are you just curious now?

 

[Richard Burns]

Try continuing the IR test across the MCB and see if the reading slowly rises, if so then this is a possible sign of dampness that is being cleared by the testing. If the reading is stable then this would be more likely an MCB fault, however that would be odd for all three if it is not moisture.
I assume there are no signs of overheating of the local busbar?

Though of course if there is a connection through the MCB then it may be picking up the RCD, that could give a low reading.

 

[HappyHippyDad]

I'm just thoroughly impressed that you've locked off the main switch.

 

[PEG]

If you are concerned,remove the MCB altogether,and test independently. Then test a known good one,or a new item,and compare...

It has been mentioned that the values are acceptable,but being mindful of the short distance you you are testing across,the likely cause of these readings,and the certainty of a customers digit being applied to it...

If it is on your mind,and the length of this thread ,suggests that,i recommend attending to both the cause,and effect of the issue....

Which may be as simple as a £3 MCB,and an umbrella....

 

[Dave OCD]

I'm just thoroughly impressed that you've locked off the main switch.

Possibly because the picture was being posted on here ?

 

[joehat]

Possibly because the picture was being posted on here ?

Nope, I either do it because I'm not trusting of others turning it back on when working on a circuit or like this scenario, I don't accident turn it back on!!