I am going to get a new meter soon (15/45) and I want to bury the line from the meter to my house; probably about 20 meters distance. They have suggested 25mm aluminum.

How should I proceed?

Check with your supply authority that they will allow Al cable underground! Our PEA office does not.

25mm² Al would be the correct size if permitted.

Ensure the cable you get is rated for underground use (that would be type NYY if in copper http://www.bangkokcable.com/catalog/BCC_CATALOG/NYY2EN.HTML )

Lay a conduit even if you get a direct-burial rated cable, means you can replace it if it fails or gets damaged.

Bury it at least 300-500mm down (deeper if under cultivated soil) with some form of protection, cable tapes will be ignored so a lean mix concrete on top of the conduit would be a better option.

What type and size of cable would be equivalent to Aluminum 25mm and acceptable for underground?

What type and size of cable would be equivalent to Aluminum 25mm and acceptable for underground?

16mm² copper NYY on this page http://www.bangkokcable.com/catalog/BCC_CATALOG/NYY2EN.HTML would certainly be acceptable to PEA on a 15/45 meter, but do check with your local office if they will allow buried Al cable as it would be significantly cheaper.

What type and size of cable would be equivalent to Aluminum 25mm and acceptable for underground?

16mm² copper NYY on this page http://www.bangkokcable.com/catalog/BCC_CATALOG/NYY2EN.HTML would certainly be acceptable to PEA on a 15/45 meter, but do check with your local office if they will allow buried Al cable as it would be significantly cheaper.

Also, check if they will allow 16mm2 copper on a 15/45 meter - some PEA's will only accept 25mm2, whether it's aluminium or copper...

Ok, time for me to ask them more questions.

Thanks guys

Some safety tips. First of all follow all electrical guidelines and do everything Crossy advises. I would go 60cm deep minimum, deeper if there is sloping to keep it as far away from landscaping and heavy machinery as you can. Put an inch of sand all around the cable to allow for movement. For warning tape, which they don't sell here anyway, another option is to use an empty 1/2" pvc pipe. Thai's won't stop digging when they hit a tape as they will think it is just some buried junk as they aren't familiar with this practice, but they might stop and ask questions if they go through a pipe.