22 AWG copper wire resistance is approximately 16.14 ohms per 1,000 ft at 20°C, or about 0.01614 ohms per foot for one conductor. That resistance may be acceptable for a short, low-current control circuit, but it becomes a meaningful source of voltage drop when conductor length, load current, or both increase.
The first number to calculate is the resistance of one conductor over the installed one-way length:
\(\displaystyle R_{\text{one conductor}} = R_{\text{per foot}} \times L\)
For 22 AWG copper:
\(\displaystyle R_{\text{one conductor}} = 0.01614 \times L\)
Where:
- (R) = conductor resistance in ohms
- (L) = one-way conductor length in feet
- 0.01614 = approximate resistance of 22 AWG copper in ohms per foot
For a two-wire DC or single-phase circuit, current travels out on one conductor and returns on the other. The circuit resistance is therefore based on the complete loop:
\(\displaystyle R_{\text{loop}} = 2 \times R_{\text{one conductor}}\)
The AWG Wire Resistance Calculator provides the conductor-resistance value needed for that first step. Use its result as an input to a voltage-drop calculation, not as a conductor ampacity determination.
Resistance by Length
The following values show approximate resistance for one 22 AWG copper conductor at common one-way lengths.
| One-Way Length | 22 AWG One-Conductor Resistance | 22 AWG Circuit Loop Resistance |
|---|---|---|
| 10 ft | 0.161 ohms | 0.323 ohms |
| 25 ft | 0.404 ohms | 0.807 ohms |
| 50 ft | 0.807 ohms | 1.614 ohms |
| 100 ft | 1.614 ohms | 3.228 ohms |
| 200 ft | 3.228 ohms | 6.456 ohms |
A 100 ft cable run is not a 100 ft electrical path for a standard two-conductor control circuit. It is normally a 200 ft round-trip path for voltage-drop purposes.
Resistance also rises as conductor temperature rises. The values above are reference values; installed conductor resistance can be higher when the wiring operates in a warm enclosure, raceway, equipment cabinet, or high-ambient environment.
22 AWG Voltage Drop Calculation
Voltage drop follows Ohm’s law:
\(\displaystyle V_{\text{drop}} = I \times R_{\text{loop}}\)
Where:
- \(V_{\text{drop}}\) = voltage lost in the conductors
- (I) = circuit current in amperes
- \(R_{\text{loop}}\) = total outgoing-and-returning conductor resistance in ohms
For a 24 VDC control circuit using 22 AWG copper, assume:
- One-way cable length: 100 ft
- Load current: 0.10 A
- 22 AWG loop resistance: 3.228 ohms
\(\displaystyle V_{\text{drop}} = 0.10 \times 3.228 = 0.323\text{ V}\)
The approximate voltage delivered to the load is:
\(\displaystyle V_{\text{load}} = 24 - 0.323 = 23.677\text{ V}\)
The voltage-drop percentage is:
\(\displaystyle \text{Voltage Drop \%} = \frac{0.323}{24} \times 100 = 1.35\%\)
A 0.323 V drop may be acceptable for one control device, but the correct field question is whether 23.68 VDC at the actual load terminals remains within the device’s operating-voltage range. A relay coil, valve actuator, sensor, controller, or electronic input may have a minimum operating voltage that is more restrictive than a general voltage-drop target.
Use the Voltage Drop Calculator when the circuit voltage, current, one-way length, and conductor size are known. For a nominal 24 VDC control circuit, the 24 VDC Control Voltage Drop Calculator keeps the calculation focused on the low-voltage control application.
22 AWG vs. 20 AWG
Moving from 22 AWG to 20 AWG lowers conductor resistance without changing the circuit layout. Approximate copper resistance for 20 AWG is 10.15 ohms per 1,000 ft, compared with approximately 16.14 ohms per 1,000 ft for 22 AWG.
Using the same 24 VDC, 100 ft one-way, 0.10 A control load:
| Conductor Size | Approx. Loop Resistance | Voltage Drop | Load Voltage | Voltage Drop |
|---|---|---|---|---|
| 22 AWG | 3.228 ohms | 0.323 V | 23.677 V | 1.35% |
| 20 AWG | 2.030 ohms | 0.203 V | 23.797 V | 0.85% |
The difference is only about 0.12 V at 0.10 A, but the benefit scales directly with load current and cable length. At 0.50 A over the same 100 ft one-way run, 22 AWG would drop about 1.61 V, while 20 AWG would drop about 1.02 V.
The wire-size choice should therefore be based on the load-voltage margin at the far end of the circuit, including normal supply variation, conductor temperature, terminal losses, splices, connectors, and any inrush or pickup current.
Control Circuit Boundaries
Resistance and voltage-drop arithmetic do not select a cable or establish conductor ampacity. The final wiring decision can also depend on insulation type, conductor material, environmental exposure, terminal rating, equipment listing, overcurrent protection, mechanical protection, raceway fill, installation method, and AHJ requirements.
A 22 AWG conductor can be physically suitable for compact control wiring, but a long run may require 20 AWG, 18 AWG, or a different circuit arrangement to maintain adequate load voltage. Circuit current must also be reviewed separately from voltage drop; a conductor with acceptable voltage drop is not automatically acceptable for the connected load or protective-device arrangement.