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OSG Ref B installation limits

WireWeHere

Table 7.1(ii) of the OSG includes Installation type B* which is "Enclosed in conduit or trunking on a wall, etc." This isn't included in any of the allowed installation methods of Table 7.1(i).

What "installation method" classification do you use when installing T&E on a blockwork wall in oval conduit, in a chase for subsequent plastering over? Equally, when the wires are just chased in and plastered over, or do you just consider that type C "clipped direct"?

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    To add to the pints already made, I would in marginal or doubtful situations go up a size and sleep soundly.

    Example , Due to an installation method that does not fit neatly into one of the standard types, there is doubt as to whether the current carrying capacity is 20 amps or 19 amps. In the case of a 16 amp circuit I would not worry since 19 or 20 amps is more than 16 amps.

    If however it was a 20 amp circuit, then I would be inclined to go up a cable size and sleep soundly. For a short run the extra cost is modest, and for a long run a larger size is likely to be required for voltage drop reasons. For a long 20 amp circuit, it is a waste of thinking to agonise as to whether 2.5mm is good for 20 amps or only for 19 amps, when you need 4mm anyway for voltage drop reasons.

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    To add to the pints already made, I would in marginal or doubtful situations go up a size and sleep soundly.

    Example , Due to an installation method that does not fit neatly into one of the standard types, there is doubt as to whether the current carrying capacity is 20 amps or 19 amps. In the case of a 16 amp circuit I would not worry since 19 or 20 amps is more than 16 amps.

    If however it was a 20 amp circuit, then I would be inclined to go up a cable size and sleep soundly. For a short run the extra cost is modest, and for a long run a larger size is likely to be required for voltage drop reasons. For a long 20 amp circuit, it is a waste of thinking to agonise as to whether 2.5mm is good for 20 amps or only for 19 amps, when you need 4mm anyway for voltage drop reasons.

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