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Fitting new fuse box and breakers

Postby p.whitelock » Thu Jul 10, 2008 6:45 pm

Hi people, new to the forum. So first off, Hi to everyone! :)

Im looking to update (and make safer) some of my houses electrics without doing a whole house re-wire. When i moved in there was alot of dodgy things (seems dodgy to me anyway) like garden lights fed from a 2.5 3 core flex and fed through drilled hole in outside wall and plugged into a socket :?

Basically i have one of the older style fuse boxes with the old cartridge fuse wire fuses. I would like to replace it with a modern nice white one with breakers in it and i want to know basic things about doing it. Im not an electrician but i do know a bit (i can test wires etc - im an instrument technician). Things like how much am i looking for the gear, how do i isolate feeds to fuses (the electric board switch me off?) etc. The supply isolation issue is my main concern as the rest of it i assume is just mark the wires and remove and refit them to the new breakers etc.

Paul :)
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Simply Build It

Postby stevenc1603 » Fri Jul 11, 2008 10:34 am

If you are in england or wales you really need a qualified pro to do this as its under the Part P regulations. Without the proper paperwork you could end up with problems selling your house in the future and you may invalidate your household insurance should the place burn down and it was proven to be an electrical fault.

If you are doing a complete re-wire then you don't have to worry about testing all the old circuits before you start. If you were just upgrading the consumer unit (fusebox) then you would want to test all the circuits first as the new MCB's and RCD's will trip for faults that the older style fuses will not as they are more sensitive.
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Postby ericmark » Fri Jul 11, 2008 10:59 am

Normally we would just tell you not really a DIY job and to get someone in but in view of you being an instrument tech I will go into pros and cons. One to change a consumer unit comes under Part P so you will need to inform LABC first before you start ignoring this could cause insurance and house selling problems. You will need to fully test, the council may also test at their expense but you need to submit your test results first and only if they don’t like the results will they re-test.
There are links to Part P and the new 17th Edition on the forum which you should read. Also the IET (formally IEE) have free download forms without the ONLINE VERSION printed on them as with Part P document. You will need a insulation tester which will test at 500 volt and a low ohm meter that uses at least 200ma on the test. Also an RCD tester which can measure both trip currents of 15ma, 30ma, 150ma and record the time taken.
If you have a TT system you will need an earth loop impedance tester or earth rod tester former being better option. An with TN-C-S it is better if you have an earth loop impedance tester. These meters are not cheap to buy about £750 not sure if you can rent as there is a problem with traceable records with rented meters never tried to rent.
If you follow the rules you would need to ask the supply agent to remove and re-instate the supply which normally means a few days without power I know many electricians just brake seals but the way the electric board react to broken seals varies area to area and there is no way I would advise you to break seals not knowing how your supply agent will react.
The boards them selves come in many versions we now have to have RCD’s on nearly everything and we are not allowed to have safety circuits on same RCD as normal sockets so at least two are required. So I will reduce to three methods.
A) A single neutral bar board with all RCBO’s this is expensive but means a fault in one circuit will not affect another.
B) A Duel RCD board normally cheaper depending on number of ways but more likely to problems with one item affecting another.
C) A board with Duel RCD and a small area for RCBO’s for smoke alarms etc.
There is massive price difference between the manufactures and short supply and you will need to shop around with RCBO vary from £12.5 to £40 each but you should be able to get a board for around the £100 mark but the cheaper boards are getting hard to find so I would not like to say how much.
One of the big problems with fitting RCD’s is faults which have not been found in the past suddenly become a real problem. Washing machines which seemed OK are found faulty etc. I would check everything first to see if you have faulty items. Also cable faults both due to insulation and borrowed neutrals the latter often being found on stairs lighting an easy mistake to make and you would not realise until you fit RCD’s there was anything wrong.
Between the cost of Part P and getting instruments it can end up with very little saving between getting a registered Part P firm to do the work to DIY and I would advise you get a quote. Because the 17th Edition only came in at the beginning of this month charges have not settled as yet but consumer units can cost £600 fully populated with RCBO’s so do make sure you know what is being offered.
If you do decide on DIY I will expect you will need more advice but I’ll wait to see your thoughts first.
Please tell us what you are doing and maybe what prices you are quoted for your area to help others considering following the same path.
Yours Eric

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