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Thread: Point of control

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    Point of control

    I have been roped into a domestic on an OLD building (you know th eone where you have to help your best clients friend out....).

    A top floor flat is being split into 2 units and totally rewired - no problem

    There is an existing supply to one flat which is in the old cloth covered cable so I suggested we pull 2 new supplies from the floor DB.

    The supply to the floor DB looks like this....

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    Now obviously its Oooooold. I did a Earth fault loop test at this point and checked there is a separate earth run up to the floor. All good (Earth fault current 0.68kA with 0.34 ohm E.F.L.I.)

    My question is - point of control.

    Am I responsible, in terms of the COC for the cable rising up to this floor. When I have worked on complexes there is meter box located some where near the flat and that I consider the point of control to be at that meter box. Am i right in saying point of control for the installation I intend to do is at the double pole isolator before the meter

    My plan is to come from the green connector block with a new cable, install a 2 suitably enclosed/rated double pole circuit breakers before going to the existing meter and another new meter (still discussing if the body corp will give me the meter or if I must install or if it must come from municipality). From there I will run 2 sub-mains to new DB board positions in the flat which has now been split into 2. Does it depend on who the meter belongs to - if yes it belongs to the body corp of the building - they bill the tenant based on that reading

    The riser cables look to be 25mm I can only see 2 phases and neutral but each phase looks to supply 2 flats.

    Now I have pointed out to the body corp the cables in the riser are old.

    In term of liability - is my point of control at the double pole circuit breakers I want to install. The body corp won't let me alter or change anything prior to this meter cupboard.

    I have checked that the earth at this point will cause effective operation of the protective devices i plan to use but I'm not keen to put my name to old school cloth cable (as I call it).

    Opinion....

  2. #2
    Diamond Member AndyD's Avatar
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    Is there a neutral-earth bond anywhere in that floor DB? From what I understand of your planned installation your point of control would be the new D/P MCB's.
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    Quote Originally Posted by AndyD View Post
    Is there a neutral-earth bond anywhere in that floor DB? From what I understand of your planned installation your point of control would be the new D/P MCB's.
    Thanks Andy. That's kind of what I thought. There is no N-E connection in the DB. I believe its a TN-S system as the earth fault loop and prospective short circuit readings were not so close.

    Just discussing with body corp who will put in the new meter and double pole isolators in.

    They are obviously not going to up grade there risers. They look in OK ish condition and if the E.F.L.I reading are ok then I am happy to connect a new sub-main to it, so new cables from supply to double pole isolator to meter and from meter to new flat DB position.

    The risers come from the LV room downstairs and they say they don't have access.

    I was just asking about the point of control because there is no way I would want to put my name to something which still has the old style cables. I advised them its time for a upgrade but no response.

    I went back and checking around the area all the flats in the area are the same story. Some of the flats have been rewired and new double pole isolators put in, existing old sub-mains as is.

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    Diamond Member AndyD's Avatar
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    The floor DB looks like it's in servicable condition so I wouldn't have an issue if the test results are good. I'd maybe include a disclaimer that given the age of the VIR wiring, whilst utmost care would be taken i'd exclude myself from liability should anything disintegrate during the installation.
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    Looks like the cabling in our apartment block. All cloth covered cable with earth wire run some time after.

    Out of curiosity how do you guys usually run new cables?
    Are these old cables typically in a conduit and you pull a new cable through (using old one or something?) or is this a cemented into the building type of situation?

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    Diamond Member AndyD's Avatar
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    How the new cables would be run would depend very much on what existing setup there is and the condition of it. With old blocks of flats there's often steel conduit from the floor DB to each flat. The old conduit can be reused but with steel conduit it can be a problem to pull new wiring or cables through because the inside can be very rough if there's been any corrosion over the years.
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    Quote Originally Posted by Gnome View Post

    Out of curiosity how do you guys usually run new cables?

    Are these old cables typically in a conduit and you pull a new cable through (using old one or something?) or is this a cemented into the building type of situation?
    If possible, use existing cable as draw wires which is first prize.

    And yup, usually in conduit. Sometime, especially if on the ground floor, the conduits have corroded and can be pig to get cables in. A lot of the time as soon as you move that cloth covered cable it just cracks or disintegrates.
    Usually with these old flat rewire the developers want to change the layout which means them knocking down wall (and losing your conduit route) which can make things tricky especially with concrete floors and ceiling.

    We are doing a small domestic (hate domestics) in a flat in an old area of Jo'burg. Wiring has been in place since the 1940's (). The developer wants to split the large top floor flat in two so we are having a nightmare in the second flat as the DB is in the first. Trying to get cable route has been.... tricky. Between false ceiling and cable in corner cornice we are nearly there.

    I checked some of the other flats - they still have rewire-able porcelain fuses with bent paper flip/bits of tin foil/small strip of coke can/bit of 2.5mm cable in them. No sign of earth leakage on anything either.

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