Best wiring thickness

Other Hardware General Electronics
1

I need to run 12V+ and Gnd from my board (mega) controlled relay to an electric strike lock, about 15 to 20 meters away.

As far as I can tell, the lock pulls about 300mA.

What would be the best wiring thickness to use for this ?

I was thinking about twin-flex - 2 core multi-strand about 0,5mm diameter.

Is the correct thickness something you just know from experience, or is there some sort of formula that I can use again in the future ?

2

Something like this:

Will allow you to calculate it.

3

daveg360:
Something like this:
Low Voltage Lighting Cable Selector | TLC Electrical

Will allow you to calculate it.

Thanks. It seems to always give me a result of 1mm wiring.

Was looking at 6W 12V 20m. Can anyone confirm this result ?

It shows :
Required Cable Size 1mm
Voltage Drop 0.5 volts.
Percentage Drop 3.8%.
Load = 0.5 amps.

4

0.5mm diameter or do you mean 0.5mm² CSA (2.1mm diameter)? they are very different.

5

daveg360:
0.5mm diameter or do you mean 0.5mm² CSA (2.1mm diameter)? they are very different.

0,5mm diameter is the thickness of the multi-strand if I expose it, lightly twist it and measure it with a vernier.

Would I be correct to think that if I use a wire that is too thin, it risks burning out, and a wire too thick will have too much resistance for the lower voltage and therefore too much current drop over the distance ?

In our area, there is only a limited choice of supplies available, so finding an online calculator that tells me I need 1 strand 0.7mm wire or 12 strand 0.2mm wire is really not much help.

So as a re-phrase to the question, is there a good practice method to determine if some available wire is suitable. For example, apply 12V to a 1m or 5m length of wire and measure the voltage at the other end ? Of course, I am (again) assuming that a too thin wire will have too much voltage drop ? What would the effect be if the wire was too thick for the application ?

6

The bigger the wire the lower is the resistance..
It will only be way to expensive.
1mm seems like the right size, the electrical instalations in houses that carry thousands of watts use wires slighty bigger than 2mm.