Key Takeaways (Executive Summary)
- The Inverse Rule: AWG works backwards. A smaller number means a thicker wire (e.g., 10 AWG is thick, 30 AWG is thin).
- Ampacity: The gauge determines how much current (Amps) the wire can carry before it melts. Undersizing wire creates a fire hazard.
- Stranded is Standard: Custom wire harnesses almost always use stranded wire (flexible) rather than solid core (rigid), which affects how the gauge is calculated.
- Distance Matters: For long runs, you may need to "upsize" the wire gauge to prevent Voltage Drop.
Why Size Matters: It’s About Safety
When designing a custom cable assembly, picking the connector is the easy part. Picking the right wire gauge is where the math happens.
AWG (American Wire Gauge) is the standardized system used in North America to define the diameter of electrically conducting wire.
If you choose a wire that is too thin (too high of a gauge) for the electrical load, the wire acts like a resistor. It heats up. At best, you get "Voltage Drop" (your 12V sensor only gets 10V). At worst, the insulation melts and starts a fire.
The Rule of Thumb: Higher Number = Thinner Wire
It is counter-intuitive, but the system is based on the manufacturing process. The "Gauge" number originally represented how many times the raw copper had to be pulled (drawn) through a die to get it to that size.
- 0 AWG (1/0): Drawn zero times. Very thick.
- 24 AWG: Drawn 24 times. Very thin.
AWG Current Carrying Capacity Chart (Ampacity)
Use this table as a baseline guideline for single core, jacketed wire in air (based on standard UL 1007 style wire at 30°C ambient).
|
AWG Size |
Diameter (mm) |
Max Amps (Chassis Wiring) |
Max Amps (Power Transmission) |
Typical Application |
|---|---|---|---|---|
|
8 AWG |
3.26 mm |
73 A |
24 A |
Battery Cables, High Power |
|
10 AWG |
2.59 mm |
55 A |
15 A |
Large Motors, Inverters |
|
12 AWG |
2.05 mm |
41 A |
9.3 A |
Household Mains, Power Tools |
|
14 AWG |
1.63 mm |
32 A |
5.9 A |
Lighting, Solenoids |
|
16 AWG |
1.29 mm |
22 A |
3.7 A |
Automotive Controls, Sensors |
|
18 AWG |
1.02 mm |
16 A |
2.3 A |
General Purpose Low Voltage |
|
20 AWG |
0.81 mm |
11 A |
1.5 A |
LED Lighting, Signals |
|
22 AWG |
0.64 mm |
7 A |
0.9 A |
Data Signals, USB Power |
|
24 AWG |
0.51 mm |
3.5 A |
0.6 A |
Ethernet, Telephone, Micro-Electronics |
> Note: "Chassis Wiring" assumes short runs in free air. "Power Transmission" is a conservative rating for bundled wires. Always check the specific UL Style sheet for your wire insulation temperature rating (e.g., 80°C vs 105°C).
Stranded vs. Solid Core: Why We Use Stranded
If you look at the wiring in the walls of your house (Romex), it is Solid Core—one single, thick piece of copper. If you look at the wiring in your car or a robot, it is Stranded—dozens of tiny hair-thin copper strands twisted together to make one wire.
Why the difference?
- Solid Core is cheap and conductive but rigid. If you vibrate it, it snaps (work hardens).
- Stranded Wire is flexible. It can survive millions of cycles of bending and vibration.
How Stranded AWG is Measured: A "24 AWG Stranded" wire is not one 24-gauge strand. It is usually 7 strands of 32 AWG twisted together. The combined cross-sectional area of copper equals that of a solid 24 AWG wire.
The Silent Killer: Voltage Drop
Just because a 24 AWG wire can handle 3.5 Amps doesn't mean it should be used for a 50-foot run.
All wire has internal resistance. The longer the wire, the higher the resistance.
- Scenario: You send 12V down a 100-foot cable to a camera using thin 24 AWG wire.
- Result: Due to resistance, only 10.5V arrives at the camera. The camera shuts off.
The Fix: For long runs, you must upsize the gauge (e.g., use 18 AWG instead of 24 AWG) to reduce resistance, even if the amperage is low.
Frequently Asked Questions (FAQ)
Q: What is the most common wire gauge for custom harnesses? A: 18 AWG to 22 AWG is the "sweet spot" for most industrial controls and sensors. It balances flexibility, current capacity, and physical strength.
Q: How do I convert Metric (mm²) to AWG? A: Europe uses square millimeters (mm²).
- 0.50 mm² ≈ 20 AWG
- 0.75 mm² ≈ 18 AWG
- 1.50 mm² ≈ 16 AWG
Q: Does insulation affect the gauge? A: No. AWG measures the conductor (copper) only. A 20 AWG wire with thick silicone insulation will look much fatter than a 20 AWG wire with thin Teflon insulation, but they carry the same current.