PFC
Prospective Fault Current
The highest that could flow at a given point if a fault of negligible occurred there — whether between live conductors or from live to earth. Every protective device must be able to break the prospective fault current at its position without failing, which is why PFC is measured or calculated at the origin of every installation.
Where PFC fits in the learning path
The Testing & Inspection section covers these units:
- Initial Verification & Dead Testing
- Live Testing
- Inspection & Certification
Curriculum mapping: C&G 2365 Unit 304 / 2391.
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
- Inspection & TestingTesting & Inspection
- Ohm's LawElectrical Science
2. Try recalling, then explore practice
Use the memory prompt below to connect the vocabulary.
- Inspection & Testing — quiz previewPlus · Testing & Inspection
- Electrical Science — quiz previewFree · Electrical Science
3. Return to the meaning
After reading or practising, explain the idea in your own words. Revisit the PFC definition to 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 highest current that would flow in a short circuit between live conductors — line to neutral, or line to line on three-phase supplies. Together with the prospective earth fault current it makes up the prospective fault current, and the larger of the two is what switchgear breaking capacity is checked against.
Compare related terms
Open a meaning to compare its role with PFC, or follow its full entry.
PSCC — Prospective Short-Circuit Current
The highest current that would flow in a short circuit between live conductors — line to neutral, or line to line on three-phase supplies. Together with the prospective earth fault current it makes up the prospective fault current, and the larger of the two is what switchgear breaking capacity is checked against.
Read the PSCC entryMCB — Miniature Circuit Breaker
An automatic switch that turns a circuit off when too much current flows, whether a slow overload or a sudden short circuit. It has replaced the rewirable fuse in modern boards. Each one is chosen by its current rating, such as 6 A for lights or 32 A for sockets, and by its type: B for most home circuits, C or D where equipment draws a big surge as it starts.
Read the MCB entryZs — Earth Fault Loop Impedance
The total opposition to current around the loop a fault current would travel. That loop runs from the supply, along the line conductor to the fault, and back through the protective conductor and the earthing. It is the supply's own part (Ze) plus the circuit's R1 + R2, the resistance of its line and protective conductors. A low Zs lets a big fault current flow, which trips the protective device quickly, so electricians measure it and compare it with the maximum allowed for that device.
Read the Zs entryA definition is a start. Using it in a real question is where it sticks.