Power over Ethernet (PoE) basics and beyond

Original Article ↗ Hacker News Discussion ↗

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.