RCCB as main switch?

[Noob2013]

Hi all,

I have been to a property where the tails come out of the meter and into an RCCB which then feeds the main switch of the consumer unit. All circuits are protected by MCBs.

If I'm adding a new circuit, is it best put in an RCBO instead of an MCB?

Thanks

 

[PEG]

Not really, I'll consider the requirements of 7671 and 7909 a bit more than most do but I sure as hell don't stick to them as if they were gospel!

Oh no,did you just say "Jehovah"?....I'll go and get some pebbles...:icon12:

 

[Guest125]

Not really, I'll consider the requirements of 7671 and 7909 a bit more than most do but I sure as hell don't stick to them as if they were gospel!

You sound like great company Dave. Fancy a beer sometime?

 

[Pete999]

Hi Noob,

A new circuit would need notifying under Part P of the building regs. As your profile shows that you're an apprentice you could maybe undertake this job with one of the electricians that you work with.

Also, if you don't already have it, get yourself access to the trainees forum.

Good advice

 

[Guest125]

Reg number please?

531.2.5 - An RCD shall be so selected and the electrical circuits so subdivided that any protective conductor current which may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device.

And:

314.1 - Every installation shall be divided into circuits, as necessary, to:

(i) avoid danger and minimise inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of hazards that may arise from the failure or a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor (PE) currents not due to a fault
(v) mitigate the effects of electromagnetic disturbances (see also chapter 44)
(vi) prevent the indirect energising of a circuit intended to be isolated.

 

[Simlec]

531.2.5 - An RCD shall be so selected and the electrical circuits so subdivided that any protective conductor current which may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device.

And:

314.1 - Every installation shall be divided into circuits, as necessary, to:

(i) avoid danger and minimise inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of hazards that may arise from the failure or a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor (PE) currents not due to a fault
(v) mitigate the effects of electromagnetic disturbances (see also chapter 44)
(vi) prevent the indirect energising of a circuit intended to be isolated.

Not fault current.
the second one basically just means don't put everything on one circuit.

 

[Guest125]

Not fault current.
the second one basically just means don't put everything on one circuit.

(i) avoid danger and minimise inconvenience in the event of a fault

This one is as clear as a bell.

 

[SPARTYKUS]

UKESrail

I think the point being made is that these Regs youve found are all admirable but they are not retrospective! The point has already been made (the analogy with a car from the past for example, without ABS).

when you quote for a job you do not have to "fix everything".

As a further example, if you fit a plastic CU today, and it turns out from the new amendment onwards all CUs need to be steel, are you then going to go back and insist they change the one you fitted a few months back?

Catch my drift?

not sure if you are on the wind up.......

 

[Guest125]

UKESrail

I think the point being made is that these Regs youve found are all admirable but they are not retrospective! The point has already been made (the analogy with a car from the past for example, without ABS).


when you quote for a job you do not have to "fix everything".

As a further example, if you fit a plastic CU today, and it turns out from the new amendment onwards all CUs need to be steel, are you then going to go back and insist they change the one you fitted a few months back?

Catch my drift?

not sure if you are on the wind up.......

Not at all.

1) The guy asked simply for the reg which I have stated.

2) My issue with the regs not being retrospective (which I fully accept is the case) is that you will need to know exactly (1) when that specific reg came into force. and (2) when the installation and subsequent alterations were carried out.

The first of these is not impossible to find out but would take days to verify beyond doubt and the 2nd will be impossible to state and would be a guess at best. The car example you gave does not work in reality because the V5 document will always have a date on. An electrical installation without all the certificates and reports made available is anyone's guess.

I do not like to work on guess' and would rather be 100% sure that I am doing the right thing. I know there is interpretation in this but this is my humble opinion.

 

[Guest125]

Not at all.

1) The guy asked simply for the reg which I have stated.

2) My issue with the regs not being retrospective (which I fully accept is the case) is that you will need to know exactly (1) when that specific reg came into force. and (2) when the installation and subsequent alterations were carried out.

The first of these is not impossible to find out but would take days to verify beyond doubt and the 2nd will be impossible to state and would be a guess at best. The car example you gave does not work in reality because the V5 document will always have a date on. An electrical installation without all the certificates and reports made available is anyone's guess.

I do not like to work on guess' and would rather be 100% sure that I am doing the right thing. I know there is interpretation in this but this is my humble opinion.

Also I would add that many lesser sparks installed 'front end' RCDs when the 17th Edition came out in an attempt to afford the installation adequate protection. So it is not unreasonable to suggest that some 'front end' RCDs have been fitted recently.

 

[Simlec]

(i) avoid danger and minimise inconvenience in the event of a fault

This one is as clear as a bell.

Not at desk at mo so no books, but how do you explain the picture near the front of your OSG regarding TT installs with a single RCD upfront? Or do you think the IET have made a mistake?

 

[Guest125]

Not at desk at mo so no books, but how do you explain the picture near the front of your OSG regarding TT installs with a single RCD upfront? Or do you think the IET have made a mistake?

I am looking at my BYB. TT installation should have a time delayed 100mA front end RCD.

 

[Simlec]

I am looking at my BYB. TT installation should have a time delayed 100mA front end RCD.

But did you not say that's not allowed? No single RCD ?
& TT installs don't have to have a 100mA time delay RCD.

 

[Guest125]

But did you not say that's not allowed? No single RCD ?

I did as a generalisation on a Sunday without my book. I did say that I would quote the specific reg. Plus TT systems have always been like this so did not feel at the time required specific mentioning. Installing a non time delayed RCD would not meet the regs quoted. A time delayed would.

 

[Guest125]

But did you not say that's not allowed? No single RCD ?
& TT installs don't have to have a 100mA time delay RCD.

You would not meet this reg if you put a 30mA non time delayed RCD at the origin of a TT installation.

I have not got every version of BS7671 printed to check when this reg came into force. Which is kind of my point.

 

[spark 68]

(i) avoid danger and minimise inconvenience in the event of a fault

This one is as clear as a bell.

That reg was already present even in the 16th edition, but was interpreted by a lot of sparks to mean only the OCPDs and final circuit arrangement, hence we had lot of upfront 30mA RCDs fitted to 16th Edition installs, the introduction of the 17th where RCD everything in domestic became the new fad, the rule was clarified further and implicitly applied to RCDs hence the so called dual RCD 17th edition boards, which itself was a 'kludge'