PoE Switch Power Budget for 8 Cameras: Calculation and Selection Guide

TL;DR

A PoE switch for 8 cameras needs a total power budget that exceeds the sum of all camera power draws plus a 20–25% margin. For typical fixed IP cameras at 10–12W each, that means a minimum 120W PoE budget — and 150W+ recommended. PoE standard (af, at, bt), cable quality, and VLAN capability also matter. This guide walks through the calculation step by step and helps you select the right switch tier.

PoE Standards: af, at, bt

Three IEEE PoE standards define maximum per-port power delivery:

• IEEE 802.3af (PoE): Up to 15.4W delivered by the switch port, 12.95W guaranteed at the powered device (PD). The difference accounts for cable resistance losses. Supports most fixed dome and bullet cameras without PTZ or heaters.
• IEEE 802.3at (PoE+): Up to 30W delivered, 25.5W at the PD. Required for PTZ cameras, cameras with integrated IR illuminators drawing more than 13W, and cameras with built-in defog heaters for cold climates.
• IEEE 802.3bt (PoE++): Type 3 up to 60W, Type 4 up to 90W at the port. Used for advanced PTZ cameras, video door stations, and powered APs. Rare for standard fixed IP cameras.

Always check the power class of each specific camera model in its datasheet — not the camera product category. A "PoE camera" could draw anywhere from 4W to 25W depending on features enabled.

Power Budget Calculation Workflow

Follow this process to size the PoE switch power budget:

1. List each camera's maximum power draw from its datasheet (not typical — use maximum). Example: 8 cameras at 12W each.
2. Sum the camera load: 8 × 12W = 96W
3. Add cable resistance loss factor: PoE power budget is measured at the switch port. The camera receives slightly less due to cable resistance. At 12.5W camera draw, the port delivers approximately 13.5–14W accounting for a 50m Cat6 run. For budgeting at the switch level, use the port delivery figure (what the switch must supply), not what the camera receives.
   Adjusted load: 8 × 13.5W = 108W
4. Add 20% headroom: 108W × 1.2 = 130W minimum PoE budget
5. Select a switch with rated PoE budget ≥ 130W — typically a 150W or 185W rated switch for this configuration.

The headroom accounts for: camera startup surge current (briefly higher than steady-state), potential future camera upgrades, and variation between individual camera units. Headroom is not optional — a switch running at 98% of its PoE budget will have unstable power delivery under transient load.

Cable Loss and Distance

Copper Ethernet cable has resistance that causes a voltage drop proportional to cable length and current. The 802.3af/at specifications account for this by defining minimum power at the PD (camera), not at the PSE (switch port). The switch must deliver more power than the camera receives.

Approximate cable power loss for PoE at maximum current:

• Cat5e, 25m run: ~0.5–0.8W loss
• Cat5e, 50m run: ~1–1.5W loss
• Cat5e, 100m run: ~2–3W loss
• Cat6, 100m run: ~1.5–2W loss (lower resistance than Cat5e)

For long runs (75–100m) with high-draw cameras (PoE+ at 25W), cable loss can reach 3–4W per port. This is why per-port and total budget calculations use port delivery watts, not camera-rated watts.

Maximum cable length for PoE is 100m (328 ft) per the 802.3 specification. Beyond 100m, use a PoE extender, a PoE injector at an intermediate location, or run fiber with a media converter and local PoE injector at the camera.

Why Headroom Matters

PoE switch power budgets are enforced by the switch firmware. When total connected PD power exceeds the switch's configured budget, the switch begins refusing power negotiation on new ports — cameras plugged in last may receive no power at all, or the switch may shut down the lowest-priority ports to protect the budget.

Operating at near-budget leaves no room for:

• Camera firmware upgrades that temporarily increase power draw during boot
• Camera startup inrush current (brief surge above steady-state draw)
• Adding a 9th camera or replacing a camera with a higher-draw model
• Temperature effects: switch PoE circuitry efficiency decreases at elevated temperatures

A 20–25% headroom margin eliminates all of these concerns at minimal cost — the price difference between a 120W and 150W PoE switch is typically under $30–50.

Switch Feature Requirements

Beyond power budget, evaluate these features for an edge AI camera deployment:

• VLAN support (802.1Q): Required to isolate camera traffic from management traffic. Only managed or smart managed switches support VLANs. Unmanaged PoE switches cannot implement VLANs.
• Port count: 8 PoE ports for cameras plus 2–3 non-PoE or uplink ports for the compute node, router, and a spare. A 10- or 12-port switch is standard for 8-camera deployments.
• Gigabit on all ports: Camera bandwidth does not require Gigabit but PoE+ power negotiation is cleaner on Gigabit ports. 100 Mbps ports are technically sufficient but are increasingly uncommon in managed switches.
• SNMP or web-based monitoring: Port-level power consumption monitoring helps identify cameras drawing near-maximum power, which may indicate hardware issues or incorrect configuration.
• PoE port scheduling (optional): Some managed switches support scheduled PoE power cycling per port — useful for rebooting cameras without physical access.

PoE Switch Tier Comparison

Example Switch Configurations

Build A: Standard indoor 8-camera deployment

• 8 fixed dome cameras at 10W each
• Camera load: 80W. With headroom: ~96W required budget minimum
• Switch: 10-port smart managed, 120W PoE budget, 802.1Q VLAN
• Uplink: Gigabit to compute node and Gigabit to router
• Cost estimate: $120–180

Build B: Outdoor 8-camera deployment with PTZ cameras

• 4 PTZ cameras at 25W each (PoE+), 4 fixed cameras at 12W each
• Camera load: 100 + 48 = 148W. With 20% headroom: 178W required
• Switch: 12-port managed PoE+ (all ports must support 802.3at), 250W PoE budget
• Requires PoE+ rated switch — not just PoE
• Cost estimate: $250–400

Build C: Industrial deployment with redundancy

• 8 cameras at 12W each in an outdoor industrial enclosure
• Camera load: 96W. With 25% headroom: 120W required
• Switch: DIN-rail industrial managed PoE, −40°C to 75°C rated, 150W PoE budget
• Cost estimate: $500–900

Common Pitfalls

• Reading per-port wattage instead of total budget: A switch with "30W per port" and 8 ports does not have a 240W PoE budget. The total PoE budget is a separate, often lower figure. Always check total PoE watts in the spec sheet.
• Mixing PoE and PoE+ cameras on a PoE-only switch: PoE-only switches (802.3af) cannot negotiate PoE+ power. A PoE+ camera will operate at reduced function or not at all — often without a clear error message at the camera or switch level.
• Assuming all switch ports share the full PoE budget equally: Some switches throttle PoE per port based on the total budget. If ports 1–4 are already delivering near-maximum power, ports 5–8 may be budget-limited even if each individual port rating is sufficient. Check whether the switch has per-port or total budget constraints.
• Using long Cat5e runs with high-draw PoE+ cameras: At 25W camera draw on 100m Cat5e cable, voltage at the camera can drop below the PoE+ minimum voltage threshold, causing the camera to reboot or operate in reduced-power mode. Use Cat6 for runs over 60m with PoE+ cameras.
• Not verifying PoE compatibility with camera brand: Some IP camera brands have reported interoperability issues with specific switch brands' PoE implementations. Test camera+switch combinations on the bench before deploying 8 units.
• No PoE port monitoring: Unmanaged switches have no visibility into per-port power draw. A camera drawing 20W on a port rated for 15.4W is invisible without managed switch monitoring — and the camera may function intermittently.

FAQ

Can I use a PoE injector instead of a PoE switch for 8 cameras?

Individual PoE injectors work for 1–2 cameras in retrofit scenarios but become cumbersome and unmanageable at 8 cameras. A PoE switch is always the correct solution for 4+ cameras — it is cheaper per port, requires one power supply, and supports centralized management.

Does it matter which PoE ports I plug cameras into on a managed switch?

On most managed switches, all PoE ports are functionally equivalent from a power perspective. Some switches prioritize lower-numbered ports when the total budget is strained. Check the switch documentation; if port priority matters, place higher-draw cameras on lower-numbered ports.

What is PoE power priority and when should I configure it?

PoE port priority (high, medium, low) determines which ports lose power first when the total PoE budget is exceeded. Set critical infrastructure (compute node management interface, primary cameras) to high priority. Secondary or redundant cameras can be low priority.

Can the PoE switch itself be powered by a UPS to protect the cameras?

Yes — and this is the correct approach. The PoE switch draws its PoE output power from the AC input. Connecting the switch to a UPS protects both the switch and all PoE-powered cameras simultaneously. Size the UPS to include full PoE switch load (switch consumption + total PoE output).

How do I discover how much power each camera is actually drawing?

On a managed switch, the web UI or SNMP MIB provides per-port PoE power consumption in real time. This is one of the most valuable features of a managed switch for edge deployments — it enables early detection of cameras drawing more power than expected due to hardware issues.

Is fiber between the switch and compute node ever necessary?

For runs under 100m, copper Gigabit is standard and sufficient. Fiber becomes relevant when the compute node is more than 100m from the switch, when electrical isolation between buildings is required (ground loop prevention), or when the run crosses areas with high electromagnetic interference.

Recommended Reading

• 8-Camera Edge AI Reference Architecture: Full PoE and Compute Design
• Networking for Edge AI: VLANs, Bandwidth Math, and Switch Selection
• Power and UPS Sizing: Including PoE Switch Load
• Storage Layout for Camera-Based Edge AI Nodes
• Jetson Deployment Checklist: Network Layer Setup