Your choice of wire depends on a few considerations:
1. Voltage. I assume that these are low-voltage heaters (<110V), so you can use what's called "hook-up wire," which generally has thinner insulation than high-voltage wire
2. Current. This will set the gauge of the wire. More on that below
3. Temperature. If the wire is near hot areas, use Teflon-insulated wire. It costs more, but it will save you a lot of trouble
4. Mechanical. If the wires have to move, you must use stranded wire. Stranded is also easier to solder
How do you select the gauge of the wire? This depends on the current that the wire has to carry as well as its length. The reason is very simple: the wire is a not a perfect conductor but rather a resistor - just like your heater. The resistance of the wire
decreases with larger wire size (lower AWG) and
increases with the length of the wire. You want to make sure that the resistance of your wire is much smaller than the resistance of your heater.
Example calculation
Here is a made-up example. Let's say that you have:
- Power of heater: P = 60 Watts
- Voltage: V = 12 Volts
- Distance from power supply to heater: d = 5 feet (accounting for the routing of the wires)
First let's figure out the
resistance of your heater, R[SUB]H[/SUB], which is calculated as:
R[SUB]H[/SUB] = V[SUP]2[/SUP]/P
R[SUB]H[/SUB] = (12[SUP]2[/SUP])/60 Ohms = 2.4 Ohms
As for the
resistance of the wire, R[SUB]W[/SUB], I would keep it at 1% of the heater's resistance (don't go above 5% if you want to push things). This would mean:
R[SUB]W[/SUB] = 0.01 * R[SUB]H[/SUB]
R[SUB]W[/SUB] = 0.01 * 2.4 Ohms = 0.024 Ohms
The
resistivity of wire, r[SUB]W[/SUB], is given as Ohms/1000 feet for standard gauge wire. The
total wire length l is
l = 2 * d, because we need to count the wire from the power supply to the heater and back
l = 2 * 5 feet = 10 feet
This means that the
maximum resistivity of the wire r[SUB]W[/SUB] we can allow is
r[SUB]W,max[/SUB] = R[SUB]W[/SUB]/l
r[SUB]W,max[/SUB] = 0.024 Ohms/10 feet = 0.0024 Ohms/foot = 2.4 Ohms/1000 feet
Now look at the
American Wire Gauge Table (column 4) to find the right
wire gauge. The results is:
AWG 13 - because its resistivity of 2.003 Ohms/1000 feet is lower than our limit of 2.4 Ohms/1000 feet
AWG 14 might be just fine as well at 2.525 Ohms/1000 feet, but AWG 13 is the one that works in a formal sense (in this example). Obviously, you will have different values of P, V, and d, so your results will be different. But I hope that this can at least point you in the right direction.
Tom