Tabulated current
It
The 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 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.
Using Tabulated current 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 Tabulated current beyond the definition?
- Explain what Tabulated current 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 Tabulated current 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 Tabulated current, 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 entryCorrection factors
Factors used with cable-rating data to account for conditions such as temperature, grouping and thermal insulation. The appropriate table, installation method and calculation must be used together; not every factor is necessarily a reduction. Cable selection also needs coordination with the protective device and checks such as voltage drop and fault protection, rather than a comparison with load current alone.
Read the Correction factors entryReference method
A described way of installing a cable, such as clipped direct or in conduit on a wall, that the current 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.
Read the Reference method entryDesign current — Ib
The current a circuit is expected to carry in normal use. For a heater or shower it's just the power divided by the voltage, but a motor's input has to be worked back from its efficiency and power factor first. It's where cable sizing starts: the device's rated current must be at least Ib, and the cable's capacity at least the device's rating.
Read the Design current entryA definition is a start. Using it in a real question is where it sticks.