The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 30 replies
  • Subscribers 31 subscribers
  • Views 18532 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Multiple circuits in a single MCB/RCBO

Former Community Member
Former Community Member
Having undertaken some inspections recently I'm finding a lot of older installations with multiple circuits within a single RCBO. Example being 2 light circuits (Upstairs/downstairs) being added to a single B6 RCBO.

The circuit design covers single pendants in each room and some downlights in the kitchen. The majority of bulbs are LED so from a risk point of view would this be unlikely to exceed 6amps. From the EICR however would this be considered C3 in peoples opinions due to risk level with a potential of splitting to separate RCBO's, or should this be C2 as there are technically 2 circuits fed from a single MCB?


Likewise the same installation has a 32amp MCB (RCD protected) supplying a ring final circuit downstairs. When work has been undertaken in the past, an additional radial circuit has been added to the same MCB in 2.5mm T&E. My view on this is that this instantly requires a C2 coding, as the radial circuit feeds multiple sockets (and there is no Fused spur within the radial line) it is not rated for the potential draw and the 32amp breaker will not trip with the overload of the radial line.


There are no spare ways in the board, so am I correct in claiming this would require a new replacement board to accommodate and separate the circuits? Would this be different if the radial only served a single double socket for ease of the wiring?


There appears to be a lot of confusion on when/if its acceptable to add radials to an existing breaker and I wondered if there was any clarity, given that these circuit amendments are historic and retrospective changing to meet current regulations is not essential providing it met previous regulations.


Many thanks

David
  • Former Community Member
    0 Former Community Member
    Dave many thanks for your thoughts and opinions. 


    I’m grateful for all the comments from everyone as it helps gain experience from those perhaps who have done the work over many years. 


    To give clarity though it’s not my intention to do the testing and reporting on an installation with a view to picking up remedial work. My entire aim is to produce reports that demonstrate that an installation is either safe or not for the occupant and give that information to the landlord for them to fulfil their own obligations to their tenant. 


    The questions have come as my original training up to and including 18th edition always gave an impression that the circuit started at the board and radials were very distinct in their arrangement with a single cable from the mcb or 2 for a ring circuit. 


    It of course does not appear that way in reality and I wouldn’t suggest an installation or circuit is unsafe unless risks were evident. Regarding the ‘Cable greening’ again this was never covered within the course so seeing this in reality caused the comment and from reading previous threads on forums I understood this to be a result of overheating cables, not reaction of the plasticiser with damp as you mentioned. 


    The point of asking on this forum was to gather opinions and views according to those who have greater experience so that I don’t unnecessarily expose myself to the risks you mention or indeed risks to others. 


    Once again thank you all who have commented.
  • 0
    I don’t think green goo gets a mention in The Wiring Regulations BS7671, it does however get a mention in the IET Guidance Notes, it’s one of those things you find out about as part of gaining experience, as you are.
  • 0

  • 0
    If there is a borrowed neutral and I combine two circuits into one I either tie the conductors together with cable ties or actually join them with Wago type connectors then take a single conductor into the CPD and neutral terminals, that should make it clear to the next guy what’s going on.
  • 0
    " My entire aim is to produce reports that demonstrate that an installation is either safe or not for the occupant and give that information to the landlord for them to fulfil their own obligations to their tenant. "


    David76,


    What DaveZ is trying to tell you is that you are not ready to do such inspections, one day you may be and it is good that you are trying to get to grips with it.

    But for now, leave well alone, it`s more than merely passing exams, it needs a wealth of experience and by asking on here you have shown you are addressing that aspect. . 

    Remember Clint Eastwood "Each man should know his limitations".


  • 0
    The government set an unrealistic timescale, there never was enough electricians who would meet the “gold standard” for electrical inspectors and that was before the delays due to Covid. There were always going to be people who will be good inspectors who need to get up to speed and everyone will learn more the more they do.


    We now have the situation where the government are refusing to extend the deadline for completion of the landlords EICRs beyond this week, because they are saying that Covid should not have held up the completion of the inspections, testing and repairs.


    The government failed to plan correctly, but now any issues will be due to electricians, not the government.
  • 0
    Well at least no one can blame the government of joined up thinking then!
  • 0
    Meanwhile, this morning's exercise in safe isolation. 

    d1482d8d726b9e4b94e07a2be339d662-original-20210326_120926.jpg
  • 0
    Never, ever assume that the circuits are connected correctly as there’s just too many idiots messing about with electrical installations.
  • 0
    So what was going on - each leg of a ring in a different MCB?

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines