Unarmoured 6.6kV in Underground

Are there any codes in your area?

Do you have to comply with them?

Where are you?

Use GI conduit.

Only you know the situation, we don't. You have to do a risk assessment before you do anything.

Make the trench, lay the PVC pipe on a previous mortar base, say about 50 mm , then cover the pipe 50 mm over top of pipe.

It will avoid some rodents to byte the pipe and the cable .

GI conduit will not last on natural terrain

That is from my back ground at same case.

You seem using the underground motor 6.6 Kv for which cable needs tobe carried there.

See the codes of the area ... GI pipe with proper solid earthing will serve the purpose but GI may need to be replaced may be in 10 yrs due to corrossion. Better if HDPE is used but there is a threat of rodents hence PCC may be needed at least in firswt 2 meters. codes may not be restricting much as such. be sure of proper earthing. check what suits better in your area...

Whether you use PVC duct or GI conduit - end result is that you are derating your current carrying capacity of your cable as compared with directly buried.

Normally cross section area of 6.6kV and higher voltage cables has sufficient margin over required area to take nominal load current - reason being of two criteria, rated current and Fault level - X section has to be selected on basis of Fault level - which is higher.

In case above holds good - that even when in duct and buried in ground - x section is sufficient to take the current with all de-rating factors applied - would prefer to use GI Conduit. Reason being that it will take care of any electromagnetic interference with controls cables running in the vicinity and resulting nuisance - specially under starting condition of motor when the current is 6 to 7 times rated current.

Our solution it is as shown in the attached sketch. The embedded conduit bends has to be suitable to the cable diameter and permissible bending radius[usually 12 times the overall diameter].The conduit inner cross section area has to be about 4 times the cable overall cross section area.[nevertheless according to NEC only 2.5 times it is required].

It seems to me it is impossible to attach the sketch. Sorry!

The problem it was the browser!