Telephone cable and power cable in same conduit?

[a1topdog]

I thought I read somewhere that telephone and power cable should not be run in the same conduit - they should be spaced a min of 50mm apart.

Can someone confirm if this is correct.

Thx.

 

[ban-all-sheds]

AIUI they must either be separated by a non-conducting barrier, or if the LV cables are MICC or have earthed armour they can all be in the same conduit, but with 50mm spacing.

But BT engineers will happily install their cables in the same 25mm surface trunking as T/E. Go figure.

 

[mapj1]

Twin and Earth in the same tube as telephone is not considered as naughty as singles. This depends if you consider the double insulation (outer jacket) to constitute an adequate insulating barrier. Certainly BT do seem to permit this, at least unofficially, but I suggest its not best practice. In reality an insulation failure is very unlikely, but if the parallel length is long (more than a few feet say) then there is a risk of clicks and pops, and funny buzzing noises on the phone line, if the load on the electrical side is noisy. The capacitive coupling between two wires 1mm diameter an inch part is only 10pF or so per metre, but high frequency transients like brush noise, and dimmer switching edges can be coupled. There is experimental evidence to suggest that such coupled interference is more disruptive to ADSL installations than voice, as the frequencies used for ADSL are supersonic.
Hope that helps.
M.

 

[a1topdog]

Thanks for the replies - both very helpful.