I have four 240V mains (United Kingdom) cables I would like to run along the side of a wall in a conduit/conduit(s).

Can you advise if it is safe to put all 4 cables in the same conduit or multiple conduits for heat considerations.

The cables themselves are standard household mains cables (3 mains wires contained inside plastic outer covering).

By conduit I mean a firm plastic rectangular plastic tubing, fitted against the skirting (bottom) of a wall in an internal household room.

Several google searches did not give be specific enough results for my requirements.

Pointers to official BSI/ISO and/or other official electrical safety standards to backup answers would be very useful.

Thank you for your help.

  • If this were North America, and we were dealing with ordinary lights and receptacles type branches, 4 circuits is the practical max allowed in 1 conduit without derating (upsizing the wires). Aug 9 '18 at 18:47
  • What does derating / upsizing mean @Harper please? How would this affect 4 separate mains cables? thank you. Aug 9 '18 at 19:19
  • derating means you would run smaller gauge wires inside to reduce heat from resistance.
    – dandavis
    Aug 9 '18 at 20:36
  • According to this ABB document, the maximal current has to be reduced to 65%. See Tabelle 7, column 4: library.e.abb.com/public/a6d7a9f5a041ca8cc12579cf00217542/…
    – xeeka
    Aug 9 '18 at 22:30
  • The 65% are valid if all cables are at high load, f.e. if used for electric room heating systems, ovens, instant water heaters. It might be important for some insurances.
    – xeeka
    Aug 9 '18 at 22:49

therobyouknow... If you google search something like " conductor size allowed in what size conduit " Like I did just now...You will come up with several charts to look at.. like this one.. https://www.constructionmonkey.com/calculations/electrical/tables/wireconduit

I'm in the United States, (and a Trump supporter so you may or may not like my answer, Joking..).. but for example if your main conductor size is #2 gauge,(and the wire size and insulation type are printed on the wire itself to out dummies like me figure this out)...then reading across the chart you would need 1 1/4" conduit for all 4 wires to be run inside safely. This assumes you know what type (copper or aluminium) wire you have and what degrees' in Celsius the wire will be operating at. Also what type of conduit your using and what type of insulation is on the wires, (see boxes above with drop down menu choices).. in the UK you should be able to find on line similar helpful charts.. Good Luck.. (BTW.. it's NEVER a bad idea to go up one size in conduit sizing.. just to be extra safe and in case you need to run an extra conductor in the future).. .


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