Theoretical question

[longdogs]

Something I have always wondered about but have been too afraid to ask...

Are there any reasons (apart from the cost) why you couldn't use much heavier cable than required, so for instance; could you wire a bed side lamp using 10mm cable? Obviously the cable wouldn't fit the terminals but are there any technical reasons?

Its ok. I'm not planning on doing it.

 

[ban-all-sheds]

Apart from physical size, unwieldiness, "tail wagging the dog" etc, no reason at all.

Why?

 

[OwainDIYer]

No, apart from physical and other suitability considerations.

In some circumstances it is perfectly sensible to install a heavier cable than currently required to allow for future increased requirements.

 

[bernardgreen]

The larger the cable the lower the volt drop along the cable. It may only be a few percent but a 3 volt drop at 20 amps is 60 watts disipated along the cable.

Bearing in mind that "wasteful" 60 watt incandescent lamps are ( legallistically ) not good for the environment then wasting 60 watts in a cable could ( should ) be seen as wastefull.

 

[Adam_151]

Though sometimes it might raise other design considerations. I know of a building which has a DNO owned 1MVA transformer in the basement, and as such the fault level is high. The main panelboards are fitted with BS88 fuse links, so no problem there, but the submains to the final DBs are over specified given the length and current needed. Mix of 50 and 70 mm cables on 100A circuits. I assume the design was to allow not much volt drop on the submains and allow plenty for final circuits. The upshot is that the fault level at the final boards is higher than it would be had the submain cables been smaller. These boards use 60898 breakers and feed final circuits wired in twin and earth. For a fault close to the board, the undersized CPC is at risk as well as the descrimination with the upstream fuses

 

[JohnW2]

...the submains to the final DBs are over specified given the length and current needed. Mix of 50 and 70 mm cables on 100A circuits. .... The upshot is that the fault level at the final boards is higher than it would be had the submain cables been smaller. These boards use 60898 breakers and feed final circuits wired in twin and earth. For a fault close to the board, the undersized CPC is at risk as well as the descrimination with the upstream fuses

True, but that's no different from the situation which would exist if the submains utilised smaller cable (say 25mm²), but were shorter in length by a factor of 2-3, is it?

Kind Regards, John