CU with main switch RCCB

DavidJ · Aug 2, 2011

Hi I am currently training through skills 4 U so only have limited knowledge on electrical requirements.
I need help with the following:
I have just had my CU periodic test and the guy testing has told me my CU has to be upgraded as it only has 1 RCCB protecting all circuits.This is also the main switch. It is a Wylex CU.
I understand that a split load CU is better, but is it a requirement for testing that have to upgrade as this it what the guy testing has said.

Any help appreciated

Thanks David

truckster · Aug 2, 2011

Your current CU does not comply with current regs however this does not mean you have to upgrade, it's up to you. Depending on the size of the RCCB, ie 100mA,30mA etc it may be worth investigating as a 100mA RCCB won't give you good enough protection for outside use etc

Octopus · Aug 2, 2011

What code did the tester give to the RCCB? Code 2 or Code 4?

IMHO its a code 4

malcolmsanford · Aug 2, 2011

Tell your tester that on page 4 of the BS 7671-2008 as this is still the one we use, to read the introduction part and then ask why it has to be upgraded!!

I agree recommend it as a single protection device does fail Reg 314.1 now, and it may as noted by Truckster be a 100mA RCCB, where now it should be 30mA.

Risteard · Aug 2, 2011

I don't think an RCCB protecting every circuit necessarily contravenes the Wiring Regulations. BS 7671 talks about minimising inconvenience in the event of a fault - but surely whether it is sufficiently inconvenient/hazardous/whatever is a matter for a risk assessment.

malcolmsanford · Aug 2, 2011

Risteard said:
I don't think an RCCB protecting every circuit necessarily contravenes the Wiring Regulations. BS 7671 talks about minimising inconvenience in the event of a fault - but surely whether it is sufficiently inconvenient/hazardous/whatever is a matter for a risk assessment.

The risk assessment part if you follow it logically as been done for you in many ways by the design of the split board and the use of 2 RCDs in it and in high integrity boards a non RCD section.

It was seen in the past especially in TT installations that an up front RCD covering the whole installation was not a good proposition and when the use of RCDs were introduced into most domestic installations as a requirement then regulation 314.1 was amended to include the part (i)

I think the IET stopped short of actually saying you can not install a single RCD to cover a whole installation because of unforeseen scenarios, but when installing a new CU upgrade IMO you would be contravening reg 314.1 by fitting just the single RCD.

Deleted member 26818 · Aug 2, 2011

If the up front RCD is 30mA then page 4 of BS7671 doesn't really come into it.
The use of a 30mA upfront RCD never really complied with earlier editions of the Regulations, which is why so called '16th boards' had a standard main switch an d an RCD protecting only some circuits.

malcolmsanford · Aug 2, 2011

Agree to a point there about the page 4, was only highlighting that the BS 7671-2008 is not retrospective, and as there is not an actual regulation in this or past regs, that tells us that an upfront RCD can not be used to cover an entire installation, then our nearest reg that does is 314.1.

IMO I still don't think in these circumstances you can tell a client that he has to upgrade a CU, you can advise him that it may be a better option.

Deleted member 26818 · Aug 2, 2011

I believe that the extra lines added in 314.1, were added in a poor attempt to clarify matters, as it was found that many people were installing up front 30mA RCDs in order to comply with Regulation 471-16 and therefore not complying with 314-01-01.