Can't test RCBO as main RCD trips first - what to do?

[terminator]

The way I see it it's simple - If it's an insulated enclosure he don't need an upfront RCD as long as all circuits are protected by RCBO's - This would comply with the requirments of a TT installation and give total discrimination.
Just get rid of the upfront RCD and replace with a main switch.

The only caveat that I would add is (just thought of) - if someone later came along and changed an RCBO for an MCB or added another circuit with one, it would then not comply with TT requirements

So perhaps back to the upfront time delayed RCD as well as RCBO's. They are the only options if you want total discrimination.

 

[terminator]

OK - Now have more time and just read OP properly. As it's 3 phase and TT, it ought to have an up front RCD - and because discrimination is an important consideration. 531.2.4. (selection of to prevent unnecessary tripping) it must be an S type when combined with downstream RCD's.

It would also come under 531.2.9. (where discrimination is necessary to prevent danger when two or more RCD's are in series). Which I read as downstream RCD's/RCBO's must be fitted. Obviously RCBO's would be costly but would be the ultimate solution with discrimination. Which is what the customer wanted.

I don't think cost considerations come into it when the Regs state clearly what is needed for compliance in this case.

 

[Jimmy Boy]

Terminator please quote the reg that tells us we have to have an upfront RCD if all circuits have 30mA protection, I'm not saying your wrong but I can't find that reg.
ATB J

 

[ackbarthestar]

I would agree that an upfront time delayed RCD, unless the tails are mechanically protected, would be required for TT.

However, I had occasion to test a TT installation where a non-delayed 'G' 100mA and 30mA RCD were connected in series.

I ramp tested the 100mA RCD to establish minimum tripping current and then applied the normal auto tests to the 30mA RCD. At 1/2 and 1 IAN you will get results for the 30mA and on 5 IAN will get a result but will loose both RCDs.

I compared the results for the 100mA and 30mA RCDs at 5 IAN and found the results to differ..... So a certain amount of discrimination will be available for excessive leakage currents

 

[Guest55]

There's no need to make childish comments, just because someone doesn't agree with your view,that's point one, point two is, you claim to have read the OP in which he states... no markings on front of RCD but assume must be 30mA non time delay.and then you say " he'll just have to look for the BS number on the main rcd."

Well he can't find it ? so what does he put in the box asking for the BSEN number ?

Keep it civil

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point 1 - you were being a smart arse with the whole " errmmmm?" and "read the op" comments - dont dish it out if you cant take it.
point 2 - it bothers me not if others have a different opinion to mine.
point 3 - He writes BS 61008 on the cert or anything else he feels is suitable.
But what BS number he writes has not been an issue in this thread until you just brought it up ?
I thought the issue was being unable to complete the rcd tests due to an inappropriate main switch device that he never installed in the first place , which you suggested that he should take responsibilty for ????

Quote " failure to investigate would make him liable"
Again , no it wouldnt.

 

[richy3333]

Read the OP ! This isn't a EICR it's a new circuit that he is commissioning ! Yes he is liable if he fails to carry out and document his test results for the circuit HE has supplied, he was suggesting that he was going to neglect the RCBO test results in favour of an upfront RCD, by his own admission he doesn't know the characteristics of so what does he put on the cert ..ermmmm ?

Think I summed up what he shoudl do in post 5:
'Just fudge the cert, cheat, lie, else like plenty of other sparks don't send them the certificate.'

 

[Jimmy Boy]

So do you think the last electrician that worked on the board wouldn't be investigated and his results and analysed ?, and if it came to light he hadn't carried out the mandatory tests on HIS new circuit you think he wouldn't be (Accused of ) being liable if someone got a belt..Your dreaming.

 

[Guest55]

What investigation ????
Whos investigating ??? where are you getting this from lol ??
Mandatory tests ?? mandatory as in law ?? which law ???
The tests he couldnt complete would be recorded with the reasons on the cert , everything above board , no lies.
Please stop digging this hole youre in.

 

[Deleted member 9648]

What the hell does it matter which RCD trips for the purpose of the cert?....If there is a requirement for RCD protection on the circuit installed and a test operates at least one within the required time jobs a goodun innit?....Whats all this nonsense about falsifying certs and legal action?????????........confused.

 

[somersetsparks]

I would just make a note of what you found, advise customer and leave it at that, however for these purpose I have a plug lead to test rcbo's whilst they asre out of the board, especially useful in off peak installs.

 

[spark 68]

What the hell does it matter which RCD trips for the purpose of the cert?....If there is a requirement for RCD protection on the circuit installed and a test operates at least one within the required time jobs a goodun innit?....Whats all this nonsense about falsifying certs and legal action?????????........confused.

Exactly WP!, it is the disconnection time that counts, the only non compliance is that the up-front RCD trips first which should be noted on the cert.

 

[Jimmy Boy]

Hole ? no hole here sunshine, I believe what I said is true, and I will stick to it, if you have a different opinion that's your entitlement, I can respect others opinions without agreeing with them.
J

 

[Guest55]

^^^Good , i like a man who sticks to his guns.
no hard feelings

 

[Jimmy Boy]

None taken fella robust discussion is the heart and soul of a good forum
ATB J

 

[Engineer54]

As you are totally relying on a RCD device for your earth fault protection on a TT system, it makes perfect sense to have an up-front 100mA S type RCD as your ''Additional'' means of protecting against faulty down stream RCD(s). Far better to have a decent back-up, when your TT system is an unstable 200 ohm Ra set-up using a twig as the earth electrode!!... lol!!