Under ground 11 kv cable

It depends upon the country, which isn't stated.

Yes you can install more than one conductor in a single conduit as long as there is no prohibition in your electrical code. We routinely install three 23KV cables in PVC conduits. Make sure the bending radius is long enough so that you don't damage your cable when pulling it in to the equipment.

It is better to install in separate conduits so that in the vent of a fault and cable burst the other cable is not damaged.In earlier days when cables were laid in In underground trenches even then 11KV and large size cables separated by suitable means though they were in the same trench.

For Clarity, what type of cable we are talking about?? 11kv- 1core or 3 core cables

Its 11kV, 3-Core, 90mm cable.

there's no restrictionwhether to lay it adjacent to other circuit. the only restriction is the derating factors which should be considered during sizing of conductors.

let me share some of my experience with all, while i working in middle east project, that country code strictly prohabitate more than one cable in single duct, cable size is 11 kv, 240 sq mm, 3c but when i worked for new british embassy in doha, qatar, it is allowed to lay more than one cable in single duct but there is a restriction of duct length, in INDIA, it is not recomonded, even multiple layer allowed under special case.

Hi, Syed Ziauddin!

It's not my area of expertise, but it seems to me that if the cables are trefoiled, there might be no adverse effects from bundling them.

In addition, if money is not an issue, you might also shield the cables with a mu metal foil and surround either the outer insulation or the conduit with grounded wire mesh to eliminate possible emf and rf propagation into the human environment near the underground tunnels.

But when is money ever not an issue?

Mark