Yes, the cable will get hot if too small for the high power tools. But what about if the cable size is more than enough to carry the amp? I think most of our house can carry more than 15amp. Will change to a bigger wire size will I save more?
Example: The vacuum is using 10amp while the 5mm size cable max can carry is 15amp. So the cable size is more than enough to carry the load. If I change to 100mm size cable which can carry max 30amp, will I save more? Will the vacuum using less amp/power if I change to thicker cable?
Change to a better lower resistance copper wire will reduce heat and can carry higher amp. But at here, where I can find this kind of cable? Can I use speaker cable or audio cable since it is the best conductive cable.

ahahhaha.... u guys really creative.  but the answer is NO.  using bigger cable will not cause the power consumption lower... and the losses in the cable are not significant as well if one take out the cable manufacturer catalogue and study the cable resistivity...  However, appropriate cable size selection shall required some calculation to determine it...

Thanks for your explanation am_eniey. I understand the wire current flow capacity between small wire and thick wire. What I still don't understand is will a thicker wire have benefit if ordinary wire is enough for the appliance power? If in imaginery way, the highway already have extra 20-30% capicity to accomodate the car, build another few lane will make the car reach the destination faster?

What I can imagine is, the appliance using 10A current and the wire suppose to carry 10A current. Because of the wire small and high resistance, some current lost to the heat a long the wire and actually is supplying maybe 1A or 2A extra in order the appliance can get 10A. Is this what you mean?

BTU = British Thermal Unit..

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Added on August 1, 2009, 1:29 pmTo futher support my previous statement... i've manage to get some technical information from Draka Cable. 

For 1.5mm sq cable, the conductor resistance is 12.1 ohm for every 1 kilometer / 1000mtr
For 2.5mm sq cable, the conductor resistance is 7.41 ohm for every 1 kilometer / 1000mtr
For 4.0mm sq cable, the conductor resistance is 4.6 ohm for every 1 kilometer / 1000mtr

so by upgrading say 2.5mm sq cable to 4.0mm sq cable, the resistance different is 2.81 ohm for every 1000 mtr or 0.00281 ohm per meter.
and for an average power point in house, the distance are or about 15meter, which work out to be 0.04215 ohm.

u think such small significant can play role in power consumption?  And, when u upgrading the cable, u will need to use a bigger cable conduit or casing... which is also cost.  However, no doubt each cable be it 1.5, 2.5 or 4.0mm have their own current capacity limitation... and as long the electrical engineer done his calculation + some safety factor, then it should be alright.

Just like ur house Syabas incoming pipe.... dont tell me if u pipe ur whole house to bigger pipe to all ur kitchen or toilet, then ur water bill is less?  does not make sense right?

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Added on August 1, 2009, 1:42 pmTo futher support my previous statement... i've manage to get some technical information from Draka Cable. 

For 1.5mm sq cable, the conductor resistance is 12.1 ohm for every 1 kilometer / 1000mtr
For 2.5mm sq cable, the conductor resistance is 7.41 ohm for every 1 kilometer / 1000mtr
For 4.0mm sq cable, the conductor resistance is 4.6 ohm for every 1 kilometer / 1000mtr

so by upgrading say 2.5mm sq cable to 4.0mm sq cable, the resistance different is 2.81 ohm for every 1000 mtr or 0.00281 ohm per meter.
and for an average power point in house, the distance are or about 15meter, which work out to be 0.04215 ohm.

u think such small significant can play role in power consumption?  And, when u upgrading the cable, u will need to use a bigger cable conduit or casing... which is also cost.  However, no doubt each cable be it 1.5, 2.5 or 4.0mm have their own current capacity limitation... and as long the electrical engineer done his calculation + some safety factor, then it should be alright.

Just like ur house Syabas incoming pipe.... dont tell me if u pipe ur whole house to bigger pipe to all ur kitchen or toilet, then ur water bill is less?  does not make sense right?

The aircon inverter not comeout just 4yrs. This technology is quite long time. It just arrive here few yrs ago but not others country. They already have inverter type long ago. We are not advance country. It depend on manufacturing when is the right time to market here.