Understanding Voltage Drop in Low-Voltage Systems
When powering equipment over long cable runs, voltage drop is a critical factor. As current flows through a cable, resistance causes the voltage at the far end to be lower than at the source. If the drop is too high, equipment may not operate correctly, may reset intermittently, or may fail to start at all. For most low-voltage AC and DC applications, the maximum acceptable voltage drop is 10% of the supply voltage.
Use the interactive calculator below for any combination of voltage, current, and cable gauge. The reference tables beneath it cover the most common installation scenarios for quick lookup.
Page Index
- Voltage Drop Calculator
- 12V DC Power Drop Chart
- 24V AC Power Drop Chart
- 5V DC Power Drop Chart
- 48V DC Power Drop Chart (PoE)
- Notes on Voltage Drop
Voltage Drop Calculator
Select your system voltage, current draw, cable gauge, and run distance. The calculator shows the voltage drop, percentage drop, voltage at the device, and maximum safe run length for the selected gauge at the 10% limit.
12V DC Power Drop / Max Cable Distance Chart
The left column lists the current draw of your device in milliamps (mA). Find your device's current draw, then read across to find the maximum cable distance for your chosen wire gauge at the 10% voltage drop limit. For example, a 12V DC camera drawing 300mA can be powered over a maximum distance of 88 metres using 18 AWG cable.
| Current Draw | 24 AWG | 22 AWG | 20 AWG | 18 AWG | 16 AWG | 14 AWG | 12 AWG |
|---|---|---|---|---|---|---|---|
| 100mA | 66 m | 104 m | 181 m | 264 m | 420 m | 670 m | 1069 m |
| 200mA | 33 m | 52 m | 91 m | 132 m | 210 m | 335 m | 535 m |
| 300mA | 22 m | 34 m | 60 m | 88 m | 140 m | 223 m | 356 m |
| 400mA | 16 m | 26 m | 45 m | 66 m | 105 m | 167 m | 267 m |
| 500mA | 13 m | 21 m | 36 m | 53 m | 84 m | 134 m | 214 m |
| 750mA | 9 m | 14 m | 24 m | 35 m | 56 m | 89 m | 142 m |
| 1000mA (1A) | 6 m | 10 m | 18 m | 26 m | 42 m | 67 m | 107 m |
24V AC Power Drop / Max Cable Distance Chart
For AC devices, power is often measured in Volt-Amps (VA). The chart below lists the power requirement in VA with the equivalent current draw in milliamps (mA). For example, a 24V AC device drawing up to 10VA (417mA) can be run up to 137 metres on 18 AWG cable.
| Power Draw | 24 AWG | 22 AWG | 20 AWG | 18 AWG | 16 AWG | 14 AWG | 12 AWG |
|---|---|---|---|---|---|---|---|
| 10 VA (417mA) | 31 m | 86 m | 87 m | 137 m | 218 m | 348 m | 552 m |
| 20 VA (833mA) | 16 m | 43 m | 43 m | 69 m | 109 m | 174 m | 276 m |
| 40 VA (1667mA) | 8 m | 21 m | 22 m | 34 m | 55 m | 87 m | 138 m |
| 50 VA (2083mA) | 6 m | 17 m | 17 m | 27 m | 44 m | 69 m | 110 m |
5V DC Power Drop / Max Cable Distance Chart
5V DC is used for USB-powered devices, Raspberry Pi and similar single-board computers, some access control readers, and small consumer electronics. Because the supply voltage is low, even small amounts of resistance cause a proportionally large percentage drop. Runs over 5V DC should be kept as short as practical, with the heaviest gauge cable the application allows.
| Current Draw | 24 AWG | 22 AWG | 20 AWG | 18 AWG | 16 AWG | 14 AWG | 12 AWG |
|---|---|---|---|---|---|---|---|
| 100mA | 28 m | 43 m | 75 m | 110 m | 175 m | 279 m | 445 m |
| 200mA | 14 m | 22 m | 38 m | 55 m | 88 m | 140 m | 223 m |
| 300mA | 9 m | 14 m | 25 m | 37 m | 58 m | 93 m | 148 m |
| 500mA | 6 m | 9 m | 15 m | 22 m | 35 m | 56 m | 89 m |
| 1000mA (1A) | 3 m | 4 m | 7 m | 11 m | 18 m | 28 m | 44 m |
48V DC Power Drop / Max Cable Distance Chart (PoE)
Power over Ethernet (PoE) systems supply 48V DC to devices such as IP cameras, wireless access points, VoIP phones, and access control readers over structured cabling. The distance figures below apply to dedicated DC power cable runs using the listed AWG gauges. For PoE over Cat cable, the relevant standard is IEEE 802.3, which defines its own maximum cable length of 100 metres for PoE installations regardless of voltage drop. These charts are intended for dedicated power cable runs to 48V DC equipment powered outside of standard PoE infrastructure.
| Current Draw | 24 AWG | 22 AWG | 20 AWG | 18 AWG | 16 AWG | 14 AWG | 12 AWG |
|---|---|---|---|---|---|---|---|
| 100mA | 266 m | 422 m | 732 m | 1066 m | 1695 m | 2700 m | 4309 m |
| 200mA | 133 m | 211 m | 366 m | 533 m | 848 m | 1350 m | 2155 m |
| 300mA | 89 m | 141 m | 244 m | 355 m | 565 m | 900 m | 1436 m |
| 500mA | 53 m | 84 m | 146 m | 213 m | 339 m | 540 m | 862 m |
| 1000mA (1A) | 27 m | 42 m | 73 m | 107 m | 170 m | 270 m | 431 m |
| 2000mA (2A) | 13 m | 21 m | 37 m | 53 m | 85 m | 135 m | 215 m |
Notes on Voltage Drop
The 10% rule: All charts above are calculated to the 10% maximum voltage drop limit. This is the widely accepted industry standard for low-voltage DC and AC power distribution. For sensitive equipment such as access control readers, some IP cameras, or precision instrumentation, a tighter limit of 5% is sometimes specified. Use the calculator above to check specific combinations against a 5% limit if required.
Cable run distance: The distance figures in all charts represent the one-way cable run from the power supply to the device. The voltage drop calculation accounts for the full circuit (current travels to the device and returns via the negative conductor), so you do not need to double the distance before looking it up.
Temperature derating: Cable resistance increases with temperature. In high ambient temperature environments (roof spaces, outdoor conduit in direct sun), derate the maximum distances above by approximately 10-15% as a conservative allowance.
Multiple devices on one run: The charts assume a single device at the end of the run. If multiple devices are powered from a single cable run with taps along its length, the voltage drop calculation is more complex. Use the calculator above for individual device runs, or contact our team for advice on multi-drop installations.
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