Testing Zs on RCBO's

[greekislandlover]

Sorry if this is a bit dumb, but it's Monday morning and I've only had on mug of coffee!

A colleague's meter (Fluke kidney shaped one) will test Zs on an RCBO quite happily, but my Robin one won't. It's been calibrated by manufacturer very recently, has new batteries and has a D lock. Firstly, I was wondering why some meters will happly measure Zs on an RCBO, and some won't. Secondly, is there anything I can do other than to put in an RCB for the test to get Zs on an RCBO? I have removed the functional earth for the test BTW.

 

[Shakey]

Sorry if this is a bit dumb, but it's Monday morning and I've only had on mug of coffee!

A colleague's meter (Fluke kidney shaped one) will test Zs on an RCBO quite happily, but my Robin one won't. It's been calibrated by manufacturer very recently, has new batteries and has a D lock. Firstly, I was wondering why some meters will happly measure Zs on an RCBO, and some won't. Secondly, is there anything I can do other than to put in an RCB for the test to get Zs on an RCBO? I have removed the functional earth for the test BTW.

well i suppose it depends what you mean by 'wont test'

do you mean you literally dont get a reading, or do you mean it trips the RCBO?

 

[Mike P]

I had the problem of some RCDs tripping with Robin test equipment. I think the technology in the Fluke is much later and far superior. The Fluke takes a lot longer to do the test so there's obviously a lot more going on in the Fluke compared to the Robin. The Zs test you are doing is really on the circuit and not the RCBO, so normal practice is to bypass the RCBO for the test or of course buy a Fluke or equivalent.

 

[KNIPEX]

have to agree the zs test on the fluke 1653 with auto test is great saves my legs lol
however we still have an old robin zs/psc tester d lock tester but this trips most of the rcbo without giving a reading.

what make rcbo are they???

also i was told if the zs is over the max allowed in the regs book and the circuit is fitted with an rcbo it still complies, even though its over it maximum, however if it was an mcb it would have to be changed.

 

[charlie]

why not calculate.
Zs = Ze+(R1+R2)

 

[mpfisher@hotmai]

Shakey will tell you max Zs permitted on your rcbo in the 17th edition will be 1667 ohms.....................

you pays ya money you take ya chance!!!!!!

 

[sparkyork]

flluke actually own robin now as well! my 1652 has a little robin sticker in the corner of it.

 

[Shakey]

Shakey will tell you max Zs permitted on your rcbo in the 17th edition will be 1667 ohms.....................

you pays ya money you take ya chance!!!!!!

Max Zs permitted on your RCBO in the 17th Edition is 1667 ohms

 

[mpfisher@hotmai]

Nice one Shakey...............

 

[greekislandlover]

Hi again. Site's been down so couldn't reply.

Shakey - I should have been clearer. The rcbo's trip out when I do the test.
Knipex - they are Crabtree ones we mostly use, but it trips on all of 'em anyway.
Charlie - it's sockets, otherwise I would calculate.

I think the answer really would be to accidentally place the meter on the road and reverse the van over it and claim a new meter from the boss. Not sure it's actually a good idea though I actually like the meter, and as we don't see that many RCBO's changing it for a breaker for the test isn't too bad. I suspect that we will see a lot more of the things now though.

 

[mattspencer]

ok, im a newly qualified spark got my ticket 4 days ago and am having a bit of a dilema. I have a standard socket circuit protected by a 32A RCBO, what is the best and safest way to recieve an accurate Zs reading, do i bypass the RCBO, if so what's the safest way, or do i just test normally as if it were a normal MCB
any help appreciated, Many thanks

 

[Tiger]

I think it is your test meter, my meggar has the function to carry out a no trip loop imp test

 

[Spudnik]

Just swap out the RCBO for a standard 32A MCB for the test, then put the RCBO back in when done.

Seems odd that 32A RCBO's are tripping when the test current, i thought, was only 25A.

 

[slocm3105]

Just swap out the RCBO for a standard 32A MCB for the test, then put the RCBO back in when done.

Seems odd that 32A RCBO's are tripping when the test current, i thought, was only 25A.

they only need 0.03A to trip remember .

And i thought that by removing the rcbo for the test and using mcb isnt technically correct as you are changing attributes of the circuit i.e RCBO for MCB etc. Probably makes no dofference at all but surely its more CORRECT to calculate the ZS if ur tester wont D lock?

 

[Guest123]

they only need 0.03A to trip remember .

And i thought that by removing the rcbo for the test and using mcb isnt technically correct as you are changing attributes of the circuit i.e RCBO for MCB etc. Probably makes no dofference at all but surely its more CORRECT to calculate the ZS if ur tester wont D lock?

By changing an RCBO for an MCB to carry out a test you are not doing anything to the actual circuit cableing, i.e length of run installation method earth fault path etc so I dont see a problem with it and indeed I did it myself, before I had a new meter.

Personally I think calculation is a bit of a "cop out" and there is no substitute for proper testing.

Cheers