CCTV Power, PoE and Pathways
IP camera power budgets, PoE switching, cable pathways and service loops.
In this lesson
- Learning outcomes
- Core theory
- Trade application
- Worked example
- Workshop task
- Fault-finding notes
- Revision questions and answers
Learning outcomes
- Explain the purpose of this topic in everyday electrical work.
- Identify the circuit conditions that must be checked before relying on a reading.
- Apply the relevant calculation, test or drawing interpretation in a supervised training scenario.
- Recognise common apprentice mistakes and unsafe assumptions.
- Record evidence in a form that another tradesperson can understand.
Core theory
Control circuits separate decision-making from power switching. A push button, sensor, timer or relay contact may control a contactor coil, while the contactor switches the load current. This makes larger loads safer and easier to automate, but it introduces new fault paths: coil supply, control neutral, interlocks, auxiliary contacts and overload contacts.
Ladder diagrams are read from supply rail to return rail, rung by rung. Apprentices should trace the conditions required for a coil to energise, then trace what the coil changes when it operates. Holding circuits, stop circuits and overload contacts are common because they create predictable behaviour during start, stop and fault conditions.
Modern electrical work often meets data, security, CCTV, EV charging, solar and automation. The electrician does not need to become every specialist at once, but should understand power requirements, segregation, earthing, surge protection, cable pathways and how to coordinate with standards and manufacturers.
Core law
Power tells you the rate of energy conversion. Energy tells you how much is used over time. Heating is proportional to current squared through resistance, so small increases in current or connection resistance can create serious heat.
Worked example
A 230 V heater draws 8.7 A. Power is about 2.0 kW. If it runs for 3 hours it uses about 6 kWh. If a loose connection has only 0.5 Ω resistance at 8.7 A, heat at that point is I²R = 37.8 W, concentrated in a tiny area.
Textbook depth: CCTV as a power, data and evidence system
An IP CCTV system has cameras, network links, PoE power, recording, storage, time synchronisation, user access and physical mounting. Image quality depends on lens choice, viewing angle, lighting, mounting height, motion, compression and recorder settings. The cabling can be perfect and the system still fail if the camera view cannot identify the target.
PoE design starts with the maximum power of every device and the total power budget. A 16-port PoE switch with a 120 W budget cannot necessarily power 16 cameras if each camera can draw 12 W. Long cable runs, outdoor devices and high-power features require extra margin.
| Design item | Question |
|---|---|
| Camera location | What must be identified: person, face, plate, vehicle, overview? |
| PoE budget | What is the maximum wattage per device and total peak load? |
| Storage | How many days, what resolution, what frame rate, what recording mode? |
| Serviceability | Can the camera and junction box be accessed safely later? |
For electricians sourcing CCTV equipment, SecurityWholesalers.com.au is a useful Australian place to buy CCTV cameras, NVRs, PoE switches and installation accessories.
Trade application
On site, this topic is rarely isolated. It connects to safety, drawings, protection, cable selection, terminations, testing and documentation. A good apprentice does not ask only “does it work?” They ask whether it is correctly supplied, correctly protected, correctly controlled, mechanically sound, suitable for the environment, and verifiable by inspection and test.
When using this material, build a notebook of standard methods. For each topic, write the normal value, the likely fault value, the test points, the instrument setting, and the action to take if the result is abnormal. This becomes a practical diagnostic map rather than a collection of memorised definitions.
Workshop practical
Wire a start/stop contactor circuit with overload contact and indicator lamps using extra-low-voltage training equipment. Draw the ladder diagram first, then compare the wiring to the drawing. Introduce one fault at a time and record symptoms.
Evidence to collect: labelled sketch, predicted readings, actual readings, explanation of differences, supervisor feedback and one improvement to your method.
Fault-finding notes
- Confirm the complaint or task requirement in plain language.
- Compare the installation against the drawing, label or expected circuit arrangement.
- Prove whether supply is present at the correct point and under the correct condition.
- Divide the circuit into smaller sections instead of testing random points.
- After repair, test the protective measure, not just the load operation.
Common apprentice mistakes
| Mistake | Why it matters | Better habit |
|---|---|---|
| Measuring voltage without a reference plan | The reading may be real, induced, back-fed or meaningless without a return path. | State the exact two points being measured and the expected value first. |
| Assuming a device is faulty because it is not operating | The fault may be supply, control, protection, return path, settings or mechanical load. | Prove each section of the circuit in sequence. |
| Recording only pass/fail | Future workers cannot see whether results were strong, marginal or abnormal. | Record actual values, conditions and instrument details. |
Assessment standard
The assessor is looking for correct interpretation of control drawings, safe separation of control and power circuits, correct coil voltage, correct overload integration and structured fault finding.
Revision questions
- What should be proven before this task is attempted on real equipment?
- Which measurement would best confirm the main idea of this lesson?
- What reading or symptom would make you stop and ask for supervision?
- How could a poor termination change the behaviour of this circuit?
- What information should be recorded for handover or assessment evidence?
Suggested answers
- Isolation, correct circuit identification, suitable supervision, correct instrument condition and an agreed safe work method.
- The measurement depends on the lesson: voltage across a component, current through a load, resistance/continuity of a path, insulation resistance between conductors, or operation time of a protective device.
- Unexpected voltage, unstable readings, signs of heat, damaged insulation, repeated protective-device operation, or any result that conflicts with the drawing.
- It can add resistance, create heat, reduce load voltage, cause intermittent operation, distort test results or prevent protective devices operating as expected.
- Circuit ID, test conditions, instrument used, actual readings, corrective actions, variations from the drawing and supervisor sign-off where required.