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3/036 t and e on domestic ring final

hertzal123

On conducting a condition report the rf was found to be wired in 3/036 on a b16 mcb.

Have calculated the csa of the live conductors to be about 1.9mm2.Subject to circuit

length,could I convert to 2 radials and use the OSG table for 1.5mm cable on a 16A

mcb?The circuit serves a small lounge and bedroom.Otherwise,suspect this would attract

a C2 code.

Thanks for any advice,Hz

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    If it's flat twin and earth cable, the cpc may be a problem if you split into 2 no. radials on B16 - dependent on the installation's prospective fault current vs let-through of the mcb. (usually the cpc for 3/036 is slightly under 1 sq mm). Similar problem to that with circuits wired in the later 1970s T&E that had 2.5/1.0.

    Would be good to know what else you've seen that might be leading towards C2?

    Are there any signs of overload? (Or have you already assessed predicted load is likely to lead to short-term small overload?) To be honest, that would be my biggest worry, especially if it's supporting a number of rooms (or a single room likely to have heavy current-using appliances).

    Other than that, it would appear (on the surface ... but of course you may know something not apparent to us in the Forum), it may be safer to leave it as a ring final circuit on a B16, than split it? Yes, it's not a "conventional circuit", but from a volt-drop and overload protection perspective, as well as adiabatic for cpc (or line conductor for L-N) in parallel would be better?

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  • 0

    If it's flat twin and earth cable, the cpc may be a problem if you split into 2 no. radials on B16 - dependent on the installation's prospective fault current vs let-through of the mcb. (usually the cpc for 3/036 is slightly under 1 sq mm). Similar problem to that with circuits wired in the later 1970s T&E that had 2.5/1.0.

    Would be good to know what else you've seen that might be leading towards C2?

    Are there any signs of overload? (Or have you already assessed predicted load is likely to lead to short-term small overload?) To be honest, that would be my biggest worry, especially if it's supporting a number of rooms (or a single room likely to have heavy current-using appliances).

    Other than that, it would appear (on the surface ... but of course you may know something not apparent to us in the Forum), it may be safer to leave it as a ring final circuit on a B16, than split it? Yes, it's not a "conventional circuit", but from a volt-drop and overload protection perspective, as well as adiabatic for cpc (or line conductor for L-N) in parallel would be better?

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