HVACopediaWire & circuit data
Copper wire sizes, voltages, colours and voltage limits.
Copper wire sizes
| AWG | Diameter (in) | Ω per 1000 ft | Rough use |
|---|---|---|---|
| 18 | 0.040 | 8.08 | Thermostat and low-voltage control (smallest common size) |
| 16 | 0.051 | 5.08 | Low-voltage control, longer runs |
| 14 | 0.064 | 3.19 | – |
| 12 | 0.081 | 2.01 | 15 A and 20 A circuits |
| 10 | 0.102 | 1.26 | 30 A circuits |
| 8 | 0.128 | 0.786 | 40 A circuits (stranded) |
| 6 | 0.184 | 0.510 | – |
| 4 | 0.232 | 0.321 | About 85 A feeders |
| 3 | 0.260 | 0.254 | – |
| 2 | 0.292 | 0.201 | – |
| 1 | 0.332 | 0.160 | – |
| 1/0 | 0.372 | 0.127 | – |
| 2/0 | 0.418 | 0.101 | – |
| 3/0 | 0.470 | 0.0797 | – |
| 4/0 | 0.528 | 0.0626 | About 230 A building service |
Resistance is at 75 °C (167 °F). The uses are rough guides only. The electrical code and correction factors decide the real size.
Common supply voltages (60 Hz)
| Voltage | Phase | Where |
|---|---|---|
| 115 / 120 V | Single | Receptacles, small motors, controls |
| 208 V | Single | Commercial buildings (from a three-phase system) |
| 230 / 240 V | Single | Homes: A/C, electric heat, dryers |
| 230 / 240 V | Three | Commercial equipment |
| 480 V | Three | Larger commercial and industrial equipment |
Colours and basics
- Ground (equipment ground) is green and never carries current in normal operation.
- The grounded conductor (neutral) is white or grey. The ungrounded (hot) conductor is black or any colour except green, white or grey.
- A 120 V circuit peaks at about ±170 V. Voltage (rms) = peak × 0.707.
- Most HVACR equipment is built for the nameplate voltage ±10%. A motor should never see less than 90%. Measure at the panel AND at the unit, with the unit running.
- A GFCI trips at about 6 mA of leakage.
- Typical fuse ratings in HVACR: 5, 10, 15, 20 and 30 A.
- Wire strippers: too large a setting leaves insulation on, too small nicks the strands and lowers the current the wire can carry.
- A short circuit trips instantly. An overload follows the normal path but draws too much, so it may trip slowly or not at all.
- Meter checks: set AC or DC first, put the leads in the right jacks, and start on a range above the expected voltage. Clamp only one conductor. Never use an ohmmeter on a live circuit.
Take it with you
All of these tables, plus the calculators, are in the HVACopedia app, offline.
Calculation aids and reference figures for licensed technicians. Always follow the manufacturer’s data plate and manual for the exact model, and local codes. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Pressures are typical saturation values and change with load and airflow.