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Protecting a sub circuit

John Boy

Hi All,

I have inherited a house with an annexe in the garden.

the annexe has a 63amp RCCB in a 6 way board with a B20 three B16 and one B6 and one spare.

the annexe is supplied by a 3 core SWA 6mm cable that runs about 40 meters. The cable runs surface mounted externally back to the meter which is external in a coveted alleyway. This cable goes back to a fused consumer unit and then via Henley blocks to the 100a meter.

I have added up all the appliances etc in the annexe and the total max wattage comes to about 10kw.

the cable size seems a bit small but changing it would not be easy. So my question is how do I protect the cable in this situation?

Parents
  • 0

    Well, before you panic, ask do you really need to ?

    Is the cable showing signs of thermal distress?, do you actually intend to run all the circuits in the annex flat out for long periods ?

    Assuming it is not buried in insulation, that  cable will be OK to run at about 50 A (about 12kW) all day, rather more on a cold day, and a lot more again for short periods of a few minutes.

    What size is the fuse at the house end, and has it ever blown ?

    You may  suffer a bit from voltage drop issues, flickering lights etc  if you do load it like that, , but this is not really a dangerous issue, more of an irritation.

    Then if you decide there really is a problem, you could reduce the fuse rating at the house end to match or be less than the cable rating, cutting supply if there is excess demand,  or you could run a new supply along side, or remove some of the heavier loads from the annex.

    Mike.

Reply
  • 0

    Well, before you panic, ask do you really need to ?

    Is the cable showing signs of thermal distress?, do you actually intend to run all the circuits in the annex flat out for long periods ?

    Assuming it is not buried in insulation, that  cable will be OK to run at about 50 A (about 12kW) all day, rather more on a cold day, and a lot more again for short periods of a few minutes.

    What size is the fuse at the house end, and has it ever blown ?

    You may  suffer a bit from voltage drop issues, flickering lights etc  if you do load it like that, , but this is not really a dangerous issue, more of an irritation.

    Then if you decide there really is a problem, you could reduce the fuse rating at the house end to match or be less than the cable rating, cutting supply if there is excess demand,  or you could run a new supply along side, or remove some of the heavier loads from the annex.

    Mike.

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