Retrofit rcbo for fuse box

Discussion in 'Electricians' Talk' started by derek_bartram, Nov 25, 2023.

  1. derek_bartram

    derek_bartram Member

    We've finally got into our new property, yay!

    A slightly surprising discovery is the mains is all fully collected and live... It's clearly useful to have some sockets to plug the drill battery charger in.

    However... The mains wiring is seriously dodgy, and in lots of no longer valid places. Given we're removing plaster off most of the walls, there's a pretty high chance of hitting an electrical line.

    While we are waiting for a new temporary site consumer unit to be installed (a priority!!!), is there a plug in rcbo available for a semi-enclosed fuse box?
  2. quasar9

    quasar9 Screwfix Select

    I very much doubt it ! There are plug in MCB from Wylex. You can use this saving you having to replace fuse wire. Suggest temporarily you use an RCBO socket for ongoing works till you get a proper rewire. You can get an electrician to wire up a few of these around the house.
  3. Wellwisher

    Wellwisher Active Member

    It is perfectly normal for mains to be live on moving in. Did you take a meter reading?

    What qualifies you to state the wiring is seriously dodgy?

    If you are worried about hitting a wire while stripping plaster (why are you stripping it anyway) turn the power off.

    Never heard of a temporary site consumer unit. We all survived for many years without RCDs with no problems. I think you are panicking unnecessarily.
  4. The Happy Builder

    The Happy Builder Screwfix Select

    This discussion is heading in the direction of getting very stupid quickly.

    In addition to general Wiring Regulations in BS7671 the additional requirements in BS7671 Section 704 for Construction and Demolition Site Installations, along with legislation such as the Electricity At Work, Health and Safety and Construction Design and Management.

    If you are expecting tradespeople people to come in and do work you need to protect them as well as yourself and your friends and family who may be at the house.

    BS7671 704.411.3.1 is particularly important, if Main Protective Bonding is not reliably connected to extraneous-conductive-parts such as an incoming metal water service pipe and the installation is earthed to a DNO TN-C-S PME earth terminal, the installation must be disconnected from the DNO earth terminal and an earth rod installed to provide TT earthing with the required RCD protection.

    As you apparently do not have any RCD protection it’s a fair assumption the earthing may be TN-C-S PME, so don’t think you can start cutting back pipework and leaving any Main Protective Bonding conductors disconnected or just disconnect the MPBs.

    The best advice I can give is turn the electric off until the temporary site electric supply consumer unit is professionally installed, tested and certified. Along with all the existing installation being disconnected.
    Last edited: Nov 25, 2023
    derek_bartram likes this.
  5. derek_bartram

    derek_bartram Member

    Thank you all for the above..

    Short answer: shame, but expected. We're now safe.

    Long answer:

    Some additional context to 'my house' which explains a few of the questions:
    • Very old property
    • Not been updated for decades
    • Been uninhabited for 6+ months
    • Previous owner died (allegedly from electrocution in the bath), before gifting to a charity.
    • Structure / layout of building does not lend itself to modern electrical standards, resulting in fairly complex install
    Yes, we did all the usual stuff, including meter readings.

    I'm no qualified electrician, however sufficiently knowledgeable to know dodgy when I see it. The grey area just between ok and not quite ok is one thing, but this is clearly dangerous.

    Temporary consumer unit allows us to do major renovation, with safety of modern protection, but without it being in the way of new services. Simply put, it's going to take time, and we need power throughout.

    Happy Builder: always nice to see an answer citing BS7671 - a good sign you know the official answer. Earth bonding is indeed as you suspect, with minimal services bonding. We've ended up essentially removing power, and all reasonable risk in the building, largely by permanently disconnecting power. Temporary consumer unit is priority 2, just after getting the terrifying propane tank disconnected! (It's not the bottle type, and yes, definitely getting a trades person to do it!)
  6. adgjl

    adgjl Screwfix Select

    That should be someone who is “Gas Safe” registered, with an LPG endorsement on their card. Beware - not everyone has LPG.
  7. Sparkielev

    Sparkielev Screwfix Select

    I use a temp board for rewires it is large board and a stand with 2 way consumer unit and 2 double sockets attached to it, I would disconnect old consumer unit and make up a temporary supply
  8. derek_bartram

    derek_bartram Member

    Thanks both

    Good tip - will double check

    Basically what we're doing - ours will be physically attached to the wall, but in a different location and clear of the existing stuff. I've also specified a 32A 240V socket for running a few bigger pieces of equipment as well.
    Sparkielev likes this.
  9. MGW

    MGW Screwfix Select

    There is a problem with temporary supplies, where I volunteer a building was bought with the idea of gutting it and then turning it into a workshop, electrics isolated, and most of the installation ripped out ready for the work, then there was a change of mind, it was realised there was a problem getting the railway lines into the building.

    So a debate started as to what to do with in, including demolish it and make it into a car park. In the mean time it is used to do repairs in, with a strict no hot work policy as no working smoke alarms, the gutters leak, so wet floor, and it has temporary power and lighting, although the latter is just 110 volt plug in stuff, and it has been like that for the 4 years I have been there, it seems now some safety issues due to mould as being so wet for so long, and state of the steel work, and still no decision has been made as to what is happening to the building, one bay made into a museum.

    This is the problem with temporary. What is temporary? What in real terms it means is the site is regarded as a building site, so all 55-0-55 volt power. This is also a problem as no RCD protection. I really don't know the answer.
    derek_bartram likes this.
  10. derek_bartram

    derek_bartram Member

    Understood, and that's an interesting perspective I'd not considered before to be honest. Temporary in my case, means sub-6 months, because I need to be living in it ASAP; the aim is to get major works completed with priority, then creature comforts (like a fitted kitchen, gaps between plasterboard finished, etc) coming later. My current priority is: gutting what needs to go, insulation, plumbing (in my case much simpler due to limited amount of it, and no central heating) + electrics (fix 1 tested at minimum). My 'temporary' consumer unit will include RCD protection - simply too risky not have it IMO.
  11. Coloumb

    Coloumb Screwfix Select

    I don't fully understand why you can't use the old CU till you can fit a permanent 18th edition CU. Semi enclosed fuses are still recognized under 7671, just fit RCD sockets if you want RCD protection.
  12. derek_bartram

    derek_bartram Member

    It's where the final proper one will go. Need the old one gone in order to put the new stuff in, and I can't do everything fast enough to suffer loss of power for that long.
  13. Coloumb

    Coloumb Screwfix Select

    So fit the permanent 18th edition CU now. I take it it's some sort of average domestic property you are renovating? If your junking the existing wiring just work out what circuits your likely to need, ground ring, 1st floor ring, kitchen white good radial, cooker, shower that sort of thing and fit an appropriately sized CU now. Then add a couple of sockets off the new CU for your current needs. Any good spark could do that for you in no time, then come back and complete the 1st/2nd fix later. Seems like a lot extra work to put in a temp one just to do the work all over again later. But up to you. Good luck!
    Last edited: Nov 30, 2023
  14. The Happy Builder

    The Happy Builder Screwfix Select

    The permanent replacement consumer unit and may not be suitable for a temporary site supply, it is not a forgone conclusion that it will be ;)

    It is not at all unusual to install a temporary consumer unit along with temporary earthing with a rod making it TT whilst renovation work is carried out, particularly when the final design has not been completed and there may be a risk that a new consumer unit may be damaged.
  15. Wellwisher

    Wellwisher Active Member

    Really! I’ve never heard of anyone doing it.
  16. adgjl

    adgjl Screwfix Select

    As a DNO, we quite often fit temporary boards - often feeding two or three double sockets next to the board. We would usually fit a 32A cutout fuse for a CU supplying a temporary board.
  17. The Happy Builder

    The Happy Builder Screwfix Select

    The IET Guidance Note Three also recommends full inspection and testing of a construction site installation every three months, which is a particularly good recommendation!
  18. The Happy Builder

    The Happy Builder Screwfix Select

    704.410.3.10 states the circuit has to have RCD protection and it’s not a matter of “if you want RCD protection” it’s an absolute necessity.
  19. Coloumb

    Coloumb Screwfix Select

    Not if he uses they use existing CU and wiring o_O
    derek_bartram likes this.
  20. Coloumb

    Coloumb Screwfix Select

    The Health and Safety and Construction Design and Management regs won't apply as it's a domestic. They can nominate a contractor if they way but otherwise n/a. Same with Electricity At Work, Health and Safety (at work) as they aren't employing anyone directly.


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