What is PoE and which class should I use for IP cameras?

PoE (Power over Ethernet, IEEE 802.3af / at / bt) delivers DC power and data over the same Cat5e/Cat6 cable. Pick 802.3af (15.4 W) for fixed lens cameras drawing under 13 W at the PD, 802.3at / PoE+ (30 W) for dome/bullet cameras with strong IR or pan-tilt, 802.3bt Type 3 (60 W) for PTZ and heaters, and Type 4 (100 W) for multi-sensor 360° cameras with heated housings.

How big should my PoE switch's power budget be?

Sum the source-side wattage of every powered device (each camera's PoE class × count, plus any PoE NVR), then add at least 20 % headroom for startup spikes and future expansion. A 16-camera 802.3at install needs about 16 × 30 = 480 W of port capacity plus ~96 W headroom — roughly a 600 W switch budget. Always check the switch spec sheet for 'total PoE power budget', not just per-port maximum.

How much voltage drop is acceptable on a long PoE run?

IEEE allows about 6 V of drop across 100 m of Cat5e. Beyond that, the PD won't reliably negotiate. This calculator estimates drop using 12.5 Ω loop resistance per 100 m (Cat5e 24 AWG, 2-pair for af/at, 4-pair for bt). For runs over 100 m, use Cat6 (lower resistance), upgrade to 802.3bt 4-pair, or add a PoE extender / mid-span injector.

Can I use a PoE injector instead of a managed PoE switch?

Yes for one to three cameras — a single-port PoE+ injector is cheaper than a managed switch and works for small home installs. For 4+ cameras or any commercial install, a managed PoE switch is mandatory: it consolidates the power budget, supports VLANs (separate camera traffic from data), enables per-port PoE control for remote reboots, and exposes link/PoE-class monitoring via SNMP for ongoing maintenance.

What's the difference between PoE 'budget' and 'per-port maximum'?

Per-port maximum is the upper bound a single port can deliver (e.g. 30 W on a PoE+ port). The total budget is the sum the switch's power supply can deliver across ALL ports simultaneously. An 8-port PoE+ switch might advertise '30 W per port' but only 120 W total — so you can power 4 cameras at 30 W, not 8. Always check the 'PoE Power Budget' line in the spec sheet.

Do PoE cameras work with non-PoE Ethernet ports?

No. A PoE-only camera (no 12 V DC input) requires a PoE source — either a PoE switch or a PoE injector inline before a regular switch. Dual-input cameras (PoE + 12 V DC) can take either, useful in retrofit installs where the existing switch is non-PoE. Always confirm 'PoE or 12 V DC' on the camera datasheet before designing the run.

PoE Budget Calculator for IP Cameras

Size your PoE switch, pick the right 802.3 class, and check cable-run voltage drop in one screen. Free — no signup.

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Number of cameras: 16

Power per camera (W at PD): 8W

Typical: 5–8 W fixed dome, 8–12 W IR bullet, 12–25 W vandal IR or mini-PTZ, 25–50 W full PTZ, 50–70 W heated PTZ or multi-sensor.

Longest cable run (Cat5e): 50 m

IEEE PoE spec guarantees 100 m on Cat5e. Past that you need Cat6, an extender, or a mid-span injector.

Include PoE NVR / recorder load(40 W)

Recommended switch + class

Recommended PoE class per port

802.3af (PoE)

Up to 15.4 W source-side, guarantees 12.95 W at the camera over 100 m Cat5e.

Switch power budget (with 20% headroom)

348 W

17 ports needed. Devices draw 168 W at the PD; source side is 290 W before headroom.

Estimated voltage drop on longest run

2.01 V → 46.0 V at PD

Cable run is within IEEE spec for the recommended class.

IEEE 802.3 PoE class reference

Class	Source W	At PD	Typical use
802.3af (PoE)	15.4 W	12.95 W	Fixed-lens domes, simple bullets
802.3at (PoE+)	30 W	25.5 W	IR bullets, vandal domes, mini-PTZ
802.3bt T3 (PoE++)	60 W	51 W	Full PTZ, IR illuminators
802.3bt T4 (Hi-PoE)	100 W	71 W	Heated PTZ, multi-sensor 360°, ALPR

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Stop guessing your switch budget

Drop your camera selection into the CCTVplanner designer and get a full PoE budget, cable schedule, and BoM in one PDF.