RCBOs (INSULATION RESISTANCE TEST)

[Jabbajaws]

Hello Everyone,

I am required to test my practical assessment soon and notice that my consumer unit has three RCBOs fitted.

There is a neutral wire and a cpc (beige) fitted from each RCBO. Am l required to remove these for an insulation resistance test which is 500V and may damage the RCBO being tested? Have you any do's and don'ts for this task, please?

Thanks, Jabbajaws...

 

[Spudnik]

Not really, as you seem to have it covered.

Just dont nuke the rcbo!

 

[stretchyboy]

remember - You are testing the circuit and not the protective device ;-)

 

[ian.settle1]

don't do an insulation test on the RCD/RCBO as some use a op amp as a comparator betwen line and neutral which will bugger it.

 

[stretchyboy]

did you do electronics as well as electrical, like i did?

 

[Jabbajaws]

Thanks for the input, guys. im required under assessment to apply the insulation test to the three RCBOs. Personally, as im unfamiliar with op amps and would rather take out the conductors and test them. The assessors will be looking for Safety & Efficiency during my practical. Do you think l will be marked down for removing the conductors and testing them for the Insulation Resistance Test? I am after all testing the circuit on this test and not the RCBOs.

 

[WayneL]

Hi mate,

I'm at a similar stage to you with regards studies.

We've been told not to terminate circuits at cu prior to

continuity testing but that we must terminate all circuits at cu

before ir tests, so I wouldn't disconnect if I were you.

I might be wrong about this but if you are ir testing at

the outgoing terminal of the rcbo (the start of your circuit) and

the rcbo is in the off position then there is no problem.

The only time it becomes an issue is when the rcbo is part

of the circuit under test eg. when testing the whole installation

at once.

Like I say, I might be wrong

Cheers,

Wayne

 

[Jabbajaws]

Thanks Wayne. That does sound quite logical...

 

[lockhes]

did mine yesterday

take live neutral out of bottom of rcbo and the cpc for that circuit out of earth bar and test like that you will need them out for continuity anyway

 

[sparkytel]

Unfortunately don't have my regs to hand but I thought the wording of the requirement for IR tests was that the tests are carried out between live conductors and live conductors to earthing arrangement - so CPC must be connected to the MET in the CU.

There is also another reg in this section (612) that requires all final circuits to be connected - so the old practice of testing on a circuit by circuit basis seems not to comply with the direct requirements of the 17th Edition. S

With regards RCBOs the regs do allow for a 250Volt test for devices which could be damaged by the 500Volt test (where its not practicable to remove them), so this could be an option, but you would need to disconnect the earth tail which will otherwise result in a low IR reading.

I don't think I've been of much help there have I???!!!?? Sorry

** I meant circuit by circuit basis with conductors disconnected!

 

[stretchyboy]

you will need to test each circuit individually otherwise you may miss things like borrowed neutrals and faults between circuits etc

 

[mikeymoo]

My heads fried now lol.. So what is best to do? Ive got a board to test that is fully populated with RCBO'S. Do i do this circuit by circuit as i always have done with all circuits b4?

 

[sparkytel]

For continuity tests individually.

With regs in front of me today, I can see no reason why you cannot carry out Insulation Resistance tests on the board as a whole with final circuits connected but distribution circuits tested separately.

Why not do a 250Volt test first, just in case you get anomalous readings caused by electronics devices, if you get the standard >99 ohms then you could up the test voltage to 500v.

If you get a low reading eg. 0.69 megs or below make sure your RCBO earth tails are disconnected before testing again at 250V then 500V if readings are satisfactory.

If you still get a low reading, likely caused by some device in circuit, cross-connect the line & neutral and test between this and the earthing arrangement (at 250v) if you get >99MOhm repeat test at 500V.

All of this complies with the 17th Edition and is the format we used in the 17th edition domestic testing DVD for NICEIC.

 

[lockhes]

My heads fried now lol.. So what is best to do? Ive got a board to test that is fully populated with RCBO'S. Do i do this circuit by circuit as i always have done with all circuits b4?

yeah and you will need to take all condutors out for each circuit to

 

[Moog]

I thought the tests with RCBO were Line and Neutral to earth with RCBO in circuit and between line and neutral without RCBO. The L+N->E does not damage the RCBO but will show insulation faults to earth