FAQs - Electrical Installations

Information on electrical installations with typical questions and answers.

Phase Power Factor (pF) is the ratio of Real Power (W) to Apparent Power (VA) at the fundamental frequency.

Icc stands for short-circuit current.

Point of Common Coupling (PCC) is the point where a building incomer is connected to the electricity distribution network.

Discrimination is the protection around a device within a Power Continuity Plan that will disconnect it, if a short-circuit or overload is applied, to prevent it from damaging other devices, and without interrupting their operation.

An Incomer is the cable carrying the mains power supply into a building from the nearest substation and Point of Common Coupling (PCC).

A Circuit-Breaker is a device inhibiting high surge currents over a set stated figure. Under such conditions the breaker will operate and the circuit is isolated.

Structured Cabling is building cabling infrastructure that consists of a number of standardised smaller elements called sub-systems.

Phase Balancing is where single phase equipment is supplied from a three phase supply, the phases need to be balanced to prevent three-phase equipment such as motors from operating incorrectly. A three-phase supply is provided to most commercial and industrial premises.

A single-phase supply consists of a single sinewave at the fundamental frequency. A three-phase supply consists of three waveforms each separated by 120º from each other. Phase is also used to refer to the difference between the voltage and current waveforms when used in relation to power factors.

Extra Low Voltage (ELV) is one of several means to prevent electric shock. The IEC defines three types of extra low voltage systems (Functional Extra Low Voltage – FELV, Protected Extra Low Voltage – PELV and Safety Extra Low Voltage (SELV) distinguished by their successively more restrictive safety properties.

Periodic inspection of a buildings electrical installation to BS 7671: Requirements for Electrical Installations (IET Wiring Regulations) is recommended:

for tenanted properties, every 5 years or at each change of occupancy – whichever is sooner
at least every 10 years for an owner-occupied home
at least every 5 years for a business
The Landlords and Tenant Act 1985 requires landlords of properties with short leases to keep the electrical wiring in repair and in proper working order.

< Return to all FAQs