PoE Voltage Drop Calculator

How to Use This Tool

This calculator is for anyone running a PoE camera a long way from the switch — out to a detached garage, a barn, a shop, a gate, or the far end of a driveway — who wants to know the camera will actually power up before pulling the cable. You’ll need three things: the cable length of the run, the cable type (Cat5e is 24 AWG; Cat6 is thicker 23 AWG and drops slightly less voltage), and roughly how many watts the camera draws.

Enter the length, choose feet or meters, pick your cable type and camera power, and the tool shows the voltage arriving at the camera plus a status: good to go, cutting it close, or over the 100 m data limit. It assumes a 48 V PoE source on standard 2-pair power (802.3af/at). If a run comes back marginal, shorten it, step up to thicker or better cable, use a higher-power PoE source, or add a midspan injector or extender partway along.

When This Tool Is Most Useful

Voltage drop is worth checking when you’re:

• Running a camera out to a detached garage, barn, shed, or outbuilding
• Reaching a gate, driveway entrance, or far corner of a property on one long cable
• Powering a high-draw camera — an IR/spotlight or a PTZ — at the end of a long run
• Using existing or unknown cable and want to rule out under-powering before you troubleshoot
• Deciding between running more cable, adding an injector, or moving the switch closer

Example Calculation

Picture a homeowner adding a camera to a detached garage at the end of a long driveway. From the NVR in the house to the garage is about 230 ft (70 m), run in Cat5e, feeding an IR camera that draws about 13 W at night.

• Run: 230 ft (70 m), Cat5e, ~13 W camera
• Voltage at the camera: about 46.4 V — a small drop from the 48 V source
• Status: good to go, and comfortably within the 328 ft data limit

Now suppose they want to reach a barn 394 ft (120 m) past the garage on one cable. The voltage would still be fine — about 45.8 V at the camera — but the run is now over the 100 m / 328 ft data limit, so it fails anyway. This is the key point: being under 328 ft doesn’t guarantee power is fine, and having plenty of voltage doesn’t rescue a run that’s too long for the data signal. The two limits are separate. The barn needs a PoE extender, a mid-run switch, or fiber for the data leg.

Voltage becomes the binding limit when the camera is hungry. Swap that driveway camera for a 25.5 W PTZ at 320 ft on Cat5e and the voltage sags to about 43.6 V — still inside the data limit, but “cutting it close” on power. Moving to Cat6 recovers it to roughly 44.5 V; a PoE+ source or an injector gives more margin still.

Common Mistakes

• Assuming under 328 ft means you’re fine. The 100 m figure is a data ceiling. Power can fall short well before it with a high-draw camera or thin cable — and can look fine on voltage while still busting the data limit.
• Using CCA (copper-clad-aluminum) cable. It’s cheap but has far higher resistance than solid copper, so it drops much more voltage on long runs. Always use solid pure-copper Cat5e or Cat6 for outdoor PoE.
• Forgetting the camera’s startup and night draw. IR illuminators and PTZ motors pull their peak power at night or on movement — exactly when a marginal run browns out. Size for the peak, not the idle number.
• Ignoring connectors and splices. Cheap keystone jacks, punch-downs, and gel splices each add resistance. A run that calculates fine can still fail if it’s full of poor terminations.
• Not accounting for cold. Outdoor runs to barns and gates get colder, and cameras with heaters draw more in winter — the worst case is a long cable feeding a heated camera on a freezing night.

Accuracy & Assumptions

This calculator estimates DC voltage drop for a 48 V PoE source on standard 2-pair power (802.3af/at), using the resistance of solid-copper Cat5e (24 AWG) or Cat6 (23 AWG). Your real result can differ because of:

• Cable quality — CCA or thin off-spec cable has much higher resistance than solid copper
• Connectors and splices — each termination, coupler, and punch-down adds a little resistance
• Temperature — copper resistance rises as it heats, so hot attic and summer runs drop a touch more
• PoE mode — 4-pair power (802.3bt) splits current over more conductors and drops less than the 2-pair mode modeled here
• Source voltage — some switches output 44–57 V rather than exactly 48 V, shifting the starting point

Treat the result as a planning estimate with a margin, not a guarantee. If a run is close to the edge, give it real headroom — better cable, a shorter path, or a stronger source.

Next Steps

Distance is one half of a PoE run; power supply is the other. Confirm your switch can actually feed every camera with the PoE Budget Calculator. Choosing gear for a longer or higher-power run? Compare the PoE standards to see which delivers more watts and voltage. For the full picture on distance, how far you can run a PoE camera covers extenders, injectors, and fiber. And when you’re ready to buy, see the best PoE switches for security cameras.

Related Resources

Related calculators & charts

• PoE Budget Calculator — make sure your switch has the total wattage to power every camera
• PoE Standards Comparison — 802.3af vs 802.3at vs 802.3bt power, voltage, and reach
• NVR Storage Calculator — size the hard drive for the same camera system

Related guides

• How Far Can You Run a PoE Camera? — the 100 m limit and how to go beyond it
• Best PoE Switches for Security Cameras — the power and features to look for

Browse all free security camera & NVR tools.

Frequently Asked Questions

How much voltage drop is acceptable for PoE?

PoE standards allow the camera to receive a lower voltage than the switch sends, but you want a comfortable margin. As a rule of thumb, keep the camera received voltage well above its minimum spec, a few volts of headroom, rather than running right at the edge. The calculator above flags when a run gets marginal.

Does cable type affect PoE voltage drop?

Yes. Solid pure-copper Cat5e or Cat6 has lower resistance and less drop than thinner or copper-clad-aluminum cable. CCA cable is cheaper but resists current more, causing extra voltage loss and unreliable power on long runs, so always choose solid copper for PoE.

What causes a PoE camera to lose power on a long cable?

It is voltage drop. Over a long run the copper resistance bleeds off voltage until the camera receives less than it needs to run reliably, so it reboots or will not power on. The fix is shorter runs, better cable, a higher-power PoE source such as PoE+ or PoE++, or a midspan injector that re-boosts power partway along the run.

Does staying under 328 feet guarantee my camera gets enough power?

No. The 100 meter (328 foot) figure is the Ethernet data limit, not a power guarantee. A high-draw camera or thin cable can sag the voltage below what the camera needs well within that distance, and a run with plenty of voltage still fails if it is longer than 328 feet, because the data signal degrades. Check both limits.

How far can you run a PoE camera?

The Ethernet data limit is 100 meters, or about 328 feet, per cable run. Power may become marginal before that on a high-draw camera or poor cable. To go farther, add a PoE extender or a midspan switch every 100 meters, or run fiber with a media converter for the long leg.

Will Cat6 reduce voltage drop compared to Cat5e?

Slightly. Cat6 uses thicker 23 AWG conductors versus Cat5e 24 AWG, so it has a little less resistance and drops marginally less voltage over the same length. On a long, high-draw run it can be enough to move a result from cutting it close to comfortable, but the bigger wins are shorter runs and a higher-power source.

Can I use a PoE injector or extender on a long run?

Yes. A midspan PoE injector adds power partway along a run, and a PoE extender repeats both data and power to push past the 100 meter limit. Both are common fixes for reaching a barn, gate, or outbuilding, though each extender segment still follows the same 100 meter rule.

Last updated: July 2, 2026