I need to feed a box in a small room. In that room will be a 20,000 BTU A/C, a few lights (flourescent), I want to be able to run some power tools and a 1 1/2 hp air compressor. Of course not all will run 24 hours, except the A/C at a high temp (26).

The problem I have is I need to run the wire about 45 meters and am only familiar with AWG. The Thai measurements I do not know and so far google has not helped. Maybe I am just slow.

I need to know what size wire to run in a conduit for this application. 3 wire I do know. Something unheard of here.

http://www.rapidtables.com/calc/wire/awg-to-mm.htm

http://www.rapidtables.com/calc/wire/awg-to-mm.htm

Found that but there are no real answers on a 45 meter run at 40 amps, 220 volts. Wiki answers have a bunch of questions from complete idiots. Ex. How many volts will 10 guage wire handle? Obviously there is more to the question and then most questions are for split 110 like in the USA.

My question is about voltage drop on 45 meters and what wire would I use for that run. When I have that answer I can use your conversion chart.

Southwire has a good calculator: http://www.southwire.com/support/voltage-drop-calculator.htm It wiil give you the usUS wire size and the you can use the conversion chart. You don't want more than a 6% drop. Hers what it says abou 220vac at 150 feet(45 meters) ;

1 conductors per phase utilizing a #8 Copper conductor will limit the voltage drop to 3.77% or less when supplying 40.0 amps for 150 feet on a 220 volt system.

You should be Okay with 4mm square.

Here's some basic rules of thumb I've derived from watching our electricians over the years:

10A circuit = 1.5mm2

16A circuit = 2.5mm2

20A circuit = 4mm2

32A circuit = 6mm2

5/15 meter = 10mm2

15/45 meter = 25mm2

30/100 meter = 35mm2

For your case, I'd say 10mm2 (7.x AWG)

@Crossy: I think you've read the conversion table wrong - 4mm2 = ~11AWG

For your 45M run @ 40A gives 10mm² with <5% voltage drop.

Calculate other solutions here http://www.doncastercables.com/technical-help/

If you're running 2 x 10mm² singles in conduit you can use a 4mm² ground conductor, or if naked use 10mm² VAF-GRD http://www.bangkokcable.com/catalog/BCC_CATALOG/VAFG2EN.HTML

Protect the run with a 50A breaker at the supply end.

Use an RCD in your sub-board to protect yourself when using power tools (we've all cut the cable).

If you're using an RCD in the sub board you could possibly save a little cash by not running the ground from your main board and using a local ground rod, in which case you could use 10mm² VAF http://www.bangkokcable.com/catalog/BCC_CATALOG/VAF2EN.HTML which may prove easier to get than the VAF-GRD.

I hesitate to wind up yet another A/C sizing debate... But, you may want to re-think putting a 20K BTU unit in a "small room", esp. since you only need 26C. Depending on how small is "small", you could probably get comfortable with 9K BTU.

"You should be Okay with 4mm square" OOPS! The calculation comes out to 8.36mm square, I don't know where I came up with 4mm other than early stages of diminished capacity or lack of caffine at 4:30 in the morning. Agree with Crossy 10 mm square is correct. But, Southwire, is a good site for quick reference.

Edited March 29, 201412 yr by wayned

I hesitate to wind up yet another A/C sizing debate... But, you may want to re-think putting a 20K BTU unit in a "small room", esp. since you only need 26C. Depending on how small is "small", you could probably get comfortable with 9K BTU.

I appreciate your concern. Here is my reasoning. The 26 degress is to keep my $1.5 million baht bike from corroding. The room is collecting heavy moisture now, in the dry season. When I work in the shop I do like to be comfortable.

The room is 4 X 6 x 3 meters. Not really small and the room is made from 3 1/2 inch SIP which probably does not have the highest total R value. The door is a big heat leaker, 6 inch wide hollow band all the way around. Eventually I will fill it with foam.

I chose 20,000 but because that ti what I was told I need for my bedroom of the same appoximate size. 5 X 5.5 X 3 meters. Other suggestions?

Ok. I now am armed with enough info to be semi dangerous. Thanks to all repliers

Just seen this

Xy bang on as usual.

Using Adiabatic you can actually use 2.5mm earth. IMHO I would use 4mm though.

45.pdf

45.pdf