Cable Losses

Just get the Amperes to handle, and calc it as ever and forever is done.

A 5% drop voltage is admited.

As far as I know , leds have to be connected to a DC system.

You will get some voltage drop but like a strand of Christmas lights the last will be as bright as the first, if you use a parallel circuit. Series will drop the last to almost no voltage,hence no illumination.So the resistance is figured differently in a series than a parallel. You can also have a series-parallel circuit. Best get an Electrician to hook it up for a few $ now will be well spent.

You did not say how many lights of 10 watts each is in the whole circuit.

Do not exceed the total wattage of the transformer supplying the whole circuit.

Why make it difficult. Use the maximum current and the maximum lenght. That will give you worst case end of line voltage. Allowing a 5% drop will tell you what gauge is required.

FWIW all the garden lights I have seen use 14 Ga wiring and they limit the number of lights to 10 with a 100 watt transformer LED typically draw so little you can safely double the number even if they are supposed to be 4 watts each.

If you really want to be finicky break each section betwen each light into a seperate circuit. But this is almost over doing it.

a: Use kirchhoff's theorems and Ohm's law to calculate the losses in the circuit, for both voltage and power. This is basic electrotechnics for highschool. For the ease in calculus you can consider a current density of about 0,8 to 1 A/mm2. In this way the maximum current for tha cable should be arround Imax=Pmax/U where: Imax =the maximum current Pmax = the maximum power consumed by the load U = the voltage (12V in your case) Knowing the max current and the current density for the cable you can choose the section of the cable. b:right. You should also add the cable losses. Also consider a power factor for the transformer, say 0,9 or 0,85 for the load is resistive. The rated power of the transformer would be the next standard value superior to the value obtained with the following formula: S=P/pf where: S= the calculated power for the transformer (VA) P= the active power consumed by the lamps (Watts) pf= power factor

Halogen is old and a heavy power user. CFLs and LEDs have good brightness and take far less current as well as having longer lives, far longer.....

Get them to be modern and also eventually save on electricity costs.....

For the voltage drops on cable size/lengths there are good calculators on the web....

Always use a thicker cable than needed, use double the maximum total current to get the cable size. Make sure it is armoured for garden usage and put in proper safety equipment.

Andy G. is right run a standard voltage drop calculation for AC circuits. Run your lighting in parallel.