Help Centre

Puzzled by something electrical? Devonia Electrical are building a library of help, advice & tips to make your life easier.


Read our brief guide to the Building Regulations to understand how they affect any work you or somebody else does on your electrical systems.


If you have a traditional fuse board, we strongly recommend you read our article explaining fuses, MCBs and RCDs.


Do you need an RCD to protect a new or modified circuit? Find out here.


If you want to know what all those test results mean, read on. This may arise because you're considering wiring your new-build yourself - is this the sort of thing you can do?


If you're carrying out electrical work yourself, read our tips and common pitfalls.


For those considering LED replacement bulbs, we have a comprehensive guide which will answer all your questions.


Bonding Conductor The main earth cable connecting your consumer unit or fuse board to your water & gas pipes.
Catenary Wire A structural wire supporting aerial cables, such as the cable between a house and shed.
CCU Consumer's Control Unit, or Consumer Unit. The distribution board containing your fuses, or in modern types, circuit breakers and RCD devices.
CPC Circuit Protecting Conductor. This is the correct BS7671 name for the earth wires in each circuit in your house, insulated in green and yellow.
Diversity Real-world current ratings, taking probable usage into account. For example, if you have 10 13-amp sockets on a ring main, it doesn't have to be rated at 130 amps - this would exceed the rating of the main fuse to your house!
Earth Leakage Fault The situation where a live cable discharges through the earthing circuit, for example if a cooker element cracks and comes into contact with the metal casing of the cooker.
Earthing Conductor The main earth cable connecting your consumer unit to your electricity supplier's earth (or to the earth spike, if you have a "TT" installation with a local earth).
Equipotential Zone The zone of metallic structures around your house which is all earthed together. This helps reduce the chances of a shock in the event of an Earth Leakage Fault.
Extra Low Voltage Up to 50V, such as low-voltage halogen light circuits. Three main types are used: FELV, PELV and SELV.
FELV Functional Extra Low Voltage. An extra-low voltage system that may not be electrically isolated from the low voltage system that supplies it, such as some types of computer power supply.
Fuse Metal wire designed to heat up and melt if the current exceeds a certain rating. Fuses will not actually trip at their rating - for example, a 20-amp fuse rated to BS88-3 will only trip at 32 amps, and even then will take over one hour to break the circuit. Except in plugs, fuses are generally now replaced by MCBs, which are designed to trip in under five seconds when rated correctly.
Low Voltage  Between 50V and 1000V, including the 230V UK mains voltage.
Line Conductor What used to be known as the Live wire - the one with brown insulation. Live now refers to both current-carrying wires, Line and Neutral.
Main Switch The primary isolation device for a domestic electricity supply, between the meter and the consumer unit. 
MCB Miniature Circuit Breaker. These detect when current exceeds a certain value and "trip", protecting cabling from excess current.
PEFC Prospective Earth Fault Current. The potential current which may flow during an Earth Leakage Fault. This must be greater than the trip value of fuses or circuit breakers in order for them to trip correctly, but not sufficiently high as to damage them before this happens.
PELV Protected Extra Low Voltage. An extra-low voltage system where the earth is shared with the low-voltage supply circuit, but the live and neutral are separated. PELV circuits may be electrically connected to other PELV circuits. 
PFC Prospective Fault Current. The greater of either the Prospective Earth Fault Current or the Prospective Short Circuit Current.
PSCC Prospective Short Circuit Current. The potential current which may flow during a short circuit, where the current flows from line to neutral cables, such as if a nail is driven through a cable. This must be greater than the trip value of fuses or circuit breakers in order for them to trip correctly.
RCBO Residual Current Circuit Breaker. Combines the functionality of an MCB and an RCD, protecting against both overcurrent and earth leakage.
RCD Residual Current Device. These detect Earth Leakage Currents and trip very quickly (typically in 40-300ms, or 0.04-0.3 seconds) if they detect a leak, such as a damaged cable or an electrocution, breaking the circuit almost instantly. RCDs are now required on many types of circuit.
SELV Separated Extra Low Voltage. An extra-low voltage system that is completely electrically isolated from the low voltage system that supplies it, such as a shaver socket in a bathroom.
Supplementary Bonding Additional local earth bonding, for example joining a bathroom radiator to the earth (CPC) of the bathroom circuits. Helps maintain the equipotential zone in high-risk areas, particularly when not protected by a RCD.

Any questions?

Devonia Electrical
13 Shute Park
Malborough, Devon TQ7 3SU


Tel: 01548 561561

Mobile: 07970 062008



Emergency contact number

In an emergency, please call 07970 062008


Elecsa registration EPP59665


Devonia Electrical is an approved electric vehicle chargepoint installer under the UK Government's Office for Low Emission Vehicles.

Devonia Electrical now offers PAT testing for domestic, commercial and industrial clients.

Devonia Electrical now accepts Bridges! If you are a member of the Kingsbridge Local Exchange Trading Scheme (LETS) you can pay part of your bill in Bridges.

New! Puzzled by something electrical? Read our comprehensive Glossary in the Help Centre section.

Check out our unique Electrical Healthcheck service for your safety and peace of mind.

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