Power over Ethernet (PoE)
18th Edition Exam Prep · C&G 2382-26 · Premium section
Power over Ethernet delivers both power and data down the same twisted pairs, which is why a camera or an access point needs one cable instead of two. It is extra-low voltage, so the shock risk is low, and that is exactly why it gets installed by people who do not think of it as electrical work at all.
The problem is heat. Current flowing in a pair produces heat in the conductors, and a conductor in the middle of a large bundle has nowhere to lose it. Bundle size, cable category, conductor cross-section, installation method and ambient temperature all feed into the same question — how warm does the middle of that bundle get. A cable with a larger conductor runs cooler for the same delivered power, which is why cable choice is a design decision rather than a purchasing one.
There is a second, quieter issue: connectors. Unplugging a live PoE connection can draw a small arc across the contacts, and repeated hot disconnection erodes them. Add the ordinary requirements — separation from mains cabling, sensible containment, and documentation so the next person knows the cable is energised — and PoE stops looking like just data.
Common questions
- Is there a free Power over Ethernet (PoE) quiz?
- Power over Ethernet (PoE) sits in the 18th Edition Exam Prep section, which is part of TradeTraining Premium — but the app is free to start, sample questions are open to everyone, and the free sections cover the fundamentals first.
- Where does Power over Ethernet (PoE) sit in the City & Guilds scheme?
- Power over Ethernet (PoE) maps to C&G 2382-26. On TradeTraining it lives in the 18th Edition Exam Prep section as bite-size lessons with practice questions.
- Do I need Power over Ethernet (PoE) for the 18th Edition exam?
- Yes — the C&G 2382-26 exam is set against the current BS 7671, and this topic is part of that ground. The exam is open book, so practising fast navigation to the right regulation matters as much as recall.
- Why does bundling PoE cables matter?
- Because every energised pair generates heat and the cables in the middle of a bundle cannot shed it. Large bundles raise the temperature of the innermost cables, which is why bundle size and cable choice are part of the design rather than an afterthought.
- Is PoE cabling extra-low voltage?
- Yes — the voltages involved sit in the extra-low voltage range, so the shock risk is small. The thermal behaviour of bundles and the erosion of connectors disconnected under load are the reasons it still needs designing and documenting.