Reference method
A described way of installing a cable, such as clipped direct or in conduit on a wall, that the ratings are built on. How easily heat escapes changes what a cable can carry, so the cable's construction picks the table and the method picks the column. If the method changes along the route, size for the stretch that sheds heat worst.
Using Reference method in context
Reviewed
A distinction worth remembering
A useful revision comparison is a short cable in open air against the same load supplied over a long route through insulation. Installation conditions, voltage drop and fault protection can change the selection. Learn the meaning of each input before treating a calculation as a design decision.
Questions to take further
- How can I revise Reference method beyond the definition?
- Explain what Reference method describes, compare it with a related term and use it in a topic question. State any assumptions and what evidence you would need before applying the idea to real work.
Sources
- Open University: relationships between electrical quantities — The relationship between voltage, current and resistance and the limits of an ohmic model.
- IET: current BS 7671 edition and updates — BS 7671:2018+A4:2026 and the main subject areas updated by Amendment 4.
- IET: earthing and bonding FAQs — Protective bonding, earthing arrangements and loop impedance.
Where Reference method fits in the learning path
The Design Calculations section covers these units:
- Sizing a Cable, Every Factor
- Volt Drop and Zs in Depth
- Fault Current, the Adiabatic Check and Device Choice
- Submains, Three-Phase Boards and Demand
Curriculum mapping: C&G 2365 Unit 305.
See this section in the full curriculum
This section is on the Plus path. Lesson availability depends on content review and your learning path.
Read, practise, return
1. Read it in context
- Cable SizingInstallation
2. Try recalling, then explore practice
Use the memory prompt below to connect the vocabulary.
- Cable Selection — quiz previewPlus · Installation
3. Return to the meaning
After reading or practising, explain the idea in your own words, then check what you remembered.
Recall a related term
Which term fits this definition? Say it to yourself, then reveal it. This is a memory prompt, with no score or saved result.
The current a conductor can carry continuously under stated installation conditions without exceeding its specified temperature limit. Cable tables give values for defined reference conditions, with adjustments where the actual conditions differ. Meeting the thermal-capacity check does not replace the other design checks, including protective-device coordination, voltage drop and fault protection.
Current-carrying capacity
Read the Current-carrying capacity entryCompare related terms
Open a meaning to compare its role with Reference method, or follow its full entry.
Current-carrying capacity — Iz
The current a conductor can carry continuously under stated installation conditions without exceeding its specified temperature limit. Cable tables give values for defined reference conditions, with adjustments where the actual conditions differ. Meeting the thermal-capacity check does not replace the other design checks, including protective-device coordination, voltage drop and fault protection.
Read the Current-carrying capacity entryTabulated current — It
The current a cable can carry under the reference conditions in BS 7671's Appendix 4 tables, before any adjustment. To choose a cable, divide the device's rating by the correction factors that apply, then find a cable whose tabulated figure is at least that. Multiply the chosen cable's It by installation factors such as Ca, Cg and Ci, and you've got its capacity as installed, Iz.
Read the Tabulated current entryThermal insulation factor — Ci
A correction factor for a cable that meets thermal insulation, which holds its heat in. A cable surrounded by insulation for more than 0.5 m is taken at half its clipped-direct rating, and a shorter stretch gets a smaller cut. If the reference method already describes the insulation, don't apply Ci on top.
Read the Thermal insulation factor entryContainment
The system that carries or encloses wiring along its route, such as conduit, trunking, tray or basket. It helps support and protect cables and keeps runs organised for installation and maintenance. The material and fixing method must suit the location and the cables; containment alone does not prove a circuit safe.
Read the Containment entryA definition is a start. Using it in a real question is where it sticks.