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Reducing cable sizes for termination agasint volt drop

MS01
Hopefully a straight forward question:- I have a development where the submains supply is 70mm² XLPE/SWA/LSF  and this is largely down to the length of run (volt drop) opposed to the current carrying capacity. However at the source end of the cable the meter that’s been installed cannot accommodate this size of cable so installing this through an isolator first can the cable size then be reduced to fit in the meter. The small cable would still be well with the current carry capacity of the circuit and line with the protection device? What are peoples thoughts? Bad practice??



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    No problem at all - the short segment of thinner cable will not make any significant difference to VD.


    The schedule of test results should specify the thinner cable.


    Sounds a bit like the situation when I needed to get some 25 mm² SWA into a 32 A commando plug.
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    Yes, a smaller cable will be fine, provided that it is still adequate for the OCPD.

    Keep the smaller cable as short as is reasonable, remember that 3 M of 25mm will have a similar effect on voltage drop as another 10 M of 70mm.
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    Thanks for the response, I just want to see what people's thoughts were. I thought this would be the case. ?
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    Extra effort to make it obvious to future installers that this has been done would be a sensible precaution . Seven foot tall letters in hi viz colours and flashing lights and screeching banshees and some would still not realise - you know what human beings can be like ?


    "Seven Foot Tall" ? Sorry about that (you gotta go metric every inch of the way!)
  • 0
    Hopefully a straight forward question:- I have a development where the submains supply is 70mm² XLPE/SWA/LSF and this is largely down to the length of run (volt drop) opposed to the current carrying capacity. However at the source end of the cable the meter that’s been installed cannot accommodate this size of cable so installing this through an isolator first can the cable size then be reduced to fit in the meter. The small cable would still be well with the current carry capacity of the circuit and line with the protection device? What are peoples thoughts? Bad practice??

    Sounds fine to me. Bad practice would be snipping strands out of the cable at the terminals to make it fit the smaller terminals.


    If it's coming after a meter on a normal DNO supply, you probably need your own overcurrent protection after the meter too (not just an isolator) - as most DNOs only mandate reliance on their fuse for the first 3m or so of consumer's cable (regardless of the actual impedances/physics).


       - Andy.
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    AJJewsbury:
    Hopefully a straight forward question:- I have a development where the submains supply is 70mm² XLPE/SWA/LSF and this is largely down to the length of run (volt drop) opposed to the current carrying capacity. However at the source end of the cable the meter that’s been installed cannot accommodate this size of cable so installing this through an isolator first can the cable size then be reduced to fit in the meter. The small cable would still be well with the current carry capacity of the circuit and line with the protection device? What are peoples thoughts? Bad practice??

    If it's coming after a meter on a normal DNO supply, you probably need your own overcurrent protection after the meter too (not just an isolator) - as most DNOs only mandate reliance on their fuse for the first 3m or so of consumer's cable (regardless of the actual impedances/physics).


    Ah, but this is described as a submain, so I assumed that it is a private meter with OCP upstream of it. I could be wrong as with any assumption.


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    Thanks right it's a private meter.

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