The cable can import a surge
A PoE camera with protected AC power may still be damaged through Ethernet. Long outdoor runs intercept induced voltage and can bridge areas with different earth potential.
Common-mode and differential-mode events differ
A common-mode surge drives several conductors together relative to earth. A differential event appears between conductors. Protection must address the relevant modes without loading the data signal excessively.
PoE adds DC power to the signal problem
The protector must carry PoE voltage and current without excessive resistance or heating. Connector quality and trace width become increasingly important at higher power.
Component coordination protects both interface and signal
High-energy components handle larger current while low-capacitance devices limit residual stress at the Ethernet transceiver. The stages should be coordinated.
Grounding is not optional
A device that diverts current to earth requires a short, effective bond. Long grounding wires and loops add inductive voltage during fast events.
Placement determines exposure
Building-entry protection limits energy entering the structure; device-end protection reduces residual stress at the equipment. In some cases fibre isolation is more reliable than copper protection.
Validation must include network performance
Electrical surge tests should be accompanied by link tests, PoE load tests, insertion-loss review and temperature measurement.
Conclusion
RJ45 and PoE surge protection is a system problem involving power, data, grounding and cable routing. The best protector is the one whose electrical and signal characteristics fit the installation.
References and scope
- IEC 61643-21 — Surge protective devices connected to telecommunications and signalling networks. Source
This article is an engineering interpretation for product selection and discussion. It does not replace applicable standards, electrical codes or appliance-manufacturer instructions.