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Thread: New plugs in old home with metal conduit

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    New plugs in old home with metal conduit

    I've got an old house with no earth rail in the db. The earth spike is connected to the main water copper pipe and the copper pipe is connected via a strap to the metal conduits in the roof. That's how the house is earthed

    I am in the process of installing new plugs. I have yet to wire anything but I've installed metal boxes with pvc conduit.

    Question 1: does the metal box need to be earthed?

    Question 2: can I install an earth rail in the empty space in my db and use the metal casing of the db as the 'main' earth point since the casing is connected to the earth spike or do I need to run a separate earth cable from the spike to the new earth rail in the db?

    Question 3: only the new plugs will be earthed via new earth cables, the rest of the house will remain earthed by the conduits, can I connect the earth wire from the twin earth cable to an existing conduit with a strap?

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    Diamond Member AndyD's Avatar
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    Yes the metal boxes would need to be earthed but using metal boxes with plastic conduit on a new circuit is not good practice.
    You can install an earth bar in the DB but also install a new wire direct from the earth rod to the new earth bar.
    I'm not fully understanding your third question but yes you can achieve earth bonding to a metal component via a mechanical copper strap.

    Does your installation have an earth leakage circuit breaker or is it an old style VOELCB? Maybe attach a few pictures if you can. All circuits or new sockets you install need to be protected by a 30mA earth leakage.

    Is the old circuit wiring rubber insulated/cotton covered wiring? Is this property belonging to you? I'd strongly urge you to consider a new DB and at the very least get a good sparky for an hour to inspect and test the main earth, the integrity of the earths on the circuits and general safety of the installation.
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    Wiring is the normal red and black wire. All circuits are connected to the 32mA earth leakage breaker. I've attached pics. Plenty space for an earth rail. What I meant by the third question is can I join the earth from the new plugs to an existing metal conduit in the roof or do I need to run it straight to the earth rail in the db?
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    You may not use the wireway as a earth and you wont get a loop impedance with that earth it should be tncs or tns. Also how do i open the attachment?

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    Platinum Member Derlyn's Avatar
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    @Mlb

    Judging by the questions you raised, it seems as if you are not a licenced and registered electrician. Please correct me if I'm wrong.

    Andy gave you some good advice when he suggested that you make use of the services of a suitably qualified electrician.

    Getting forum assistance is wonderful if you want fishing tips, gardening tips or some tips on how to build a cupboard or some wooden chairs, however, when it comes to electricity that can kill, it's advisable to leave it to someone who knows what they are doing.

    There is a very good reason why the law is crystal clear that only qualified and registered electricians may do electrical installation work, or, the person carrying out the work must be under the direct supervision of the registered person.

    It's not worth it taking chances. Someone might pay for it with their life.

    Have a blessed day.

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    I would install an earth bar in the DB, pull at least a 6 mm earth wire into the roof space, install an earth terminal block in the roof space.

    I would then pull and earth wire from the meter box to the terminal block in the roof space, if there is one already, link it to the terminal block. Make sure that the bonding straps between all the pipes (not rusted) are secure.

    I would then cable tie earth wires to the old metal conduit to all the critical points, like the geyser, the ceiling fans and other metal light fittings.

    Install bonding straps with a 2.5 mm earth wire linked to all the conduits above the socket outlet drops and fit a lug with an earthing screw to the metal box and connect to the earth point on the socket outlet.

    You can never have too many earth wires.

    I had to do a COC for an old house a while back, ended up installing 100 m of earth wires and spent time installing earth tails on all the metal boxes (light switches and plugs), even though the socket outlets and switches where the old metal lumex type.

    The most common problem I find with old houses where the socket outlets and switches have been replaced with plastic, no earth wire between the metal box and the outlet or switch. It shows the lack of qualifications and skills combined, they just dont understand basic electrical. Just because you have installed 50 000 socket outlets, it doesn't mean you know how to do it right, we are seeing this with the solar industry, installers brag about their 50 plus installs, but a qualified skilled electricians with experience will be able to point many non compliant parts. Any fool can assemble simple mechanical components, we did it in pre school.
    Comments are my opinion, unless regulations are attached to support the comment. This is social media, not a court room.

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