Power over Ethernet (PoE) basics and beyond

Original Article ↗ Hacker News Discussion ↗

Power over Ethernet (PoE) is highlighted as a powerful way to deliver both data and up to ~90 W of DC power over standard Ethernet cabling, enabling clean installations for cameras, Wi‑Fi access points, phones, small switches, and even lighting. Commenters contrast standards‑based IEEE PoE (802.3af/at/bt), which negotiates power safely, with non‑standard “passive PoE,” which can damage equipment if misused, and emphasize design concerns like cable limits, efficiency losses, heat, isolation, and surge protection. They also explore real‑world use cases (home and enterprise CCTV, Wi‑Fi 6/7, PoE‑powered edge switches, PoE lighting), network segmentation for security, and why PoE remains underused in consumer gear despite its practical advantages.

10G PoE and When It’s Useful

  • 802.3bt (PoE++) formally supports up to 10GBASE‑T; earlier PoE+ only covered up to 1G.
  • 10G PoE switches exist from major vendors, but commenters say real demand is niche: broadcast video production, high‑end Wi‑Fi 6/7/8 APs, compact remote switches, and some NAS/fast storage workflows.
  • Many argue most APs are airtime‑, not uplink‑limited, so 10G+PoE is usually overkill.
  • PoE Type 4 can deliver ~90 W at the source, ~70 W at the device—enough for fairly powerful terminals or small computers.

Power Capacity, Cables, and Efficiency

  • Mains IEC/Edison cords carry far more power (10–15 A, ~1200–1800 W) versus PoE’s ~1.5 A/90 W.
  • Each PoE device needs its own cable and port, unlike a power strip.
  • PoE has extra conversion losses: AC→48 V at the switch, line losses in thin copper, then 48 V→device voltage; less efficient than local DC supplies, especially at higher power.
  • Compared to powerline networking, PoE over Cat5/6 is described as faster and more reliable; mains wiring has stricter code requirements.

Standards vs Passive PoE and Safety

  • Strong consensus: use IEEE 802.3af/at/bt gear; avoid “passive PoE.”
  • Standards-based PoE negotiates before enabling power and is widely reported to be safe even when every port is PoE‑enabled.
  • Passive PoE puts fixed voltage on pins and can burn non‑PoE ports, partly because some magnetics terminate common‑mode signals via 75 Ω resistors to ground.
  • Some label passive runs aggressively; most don’t label standards‑based PoE at all.

Home CCTV, Privacy, and Camera Choices

  • Many use PoE for DIY CCTV: one cable per camera, no batteries, no cloud vendor.
  • Popular approach: PoE IP cameras (often ONVIF/RTSP), local NVR software (e.g., Frigate, Synology Surveillance, Scrypted), cameras isolated on a VLAN with no internet access.
  • Mixed experiences with brands; sensor size and low‑light performance are emphasized over megapixels. Industrial/surplus cameras are valued for fewer cloud ties and better build.

Network Segmentation and Physical Access

  • Concern: an attacker unplugging an external camera and connecting a laptop.
  • Suggested mitigations: VLANs dedicated to CCTV, private VLAN/port isolation, firewall rules (only NVR→camera, no outbound from cameras), sometimes 802.1X/MACsec.
  • Some say if someone can reach the cable unnoticed, your physical security is already failing.

PoE in Consumer and “Enterprise” Gear

  • Many want PoE in more consumer devices (streamers, hubs, small switches, laptops via splitters) to cut wall‑warts and centralize backup power.
  • Debate over what “enterprise‑grade” means: some equate it with 48‑port chassis; others with features (VLANs, QoS, routing, centralized management) regardless of port count.
  • Passive PoE’s legacy in some ecosystems (notably WISP gear) is criticized as a long‑term safety and interoperability problem.

Design and Implementation Notes

  • Engineers stress: obey isolation requirements, handle chassis grounding carefully, and “don’t skimp on TVS” for surge protection.
  • Ideal‑diode full‑bridge rectifiers (MOSFET‑based) are praised for efficiency in PoE power entry.
  • Recommendation to follow vendor PoE reference designs (TI, Microchip, etc.) rather than improvising.
  • Midspan injectors are clarified: they completely break and re‑inject power, so there’s never more than one source on a cable; PoE negotiation does not pass through.

PoE Lighting and Creative Uses

  • PoE lighting discussed as attractive (low‑voltage install, fine‑grained control, no electrician) but with gotchas: dependence on network/server, voltage drop, and life‑safety coupling.
  • Some already run rooms or basements entirely from PoE++ with DC LED bulbs.
  • Commenters fantasize about a standard PoE lighting ecosystem and various “fun” PoE‑powered gadgets given the many unused PoE ports in home switches.