Demystifying Jargon

Sometimes electricians sound like they are speaking another language! At Station Electrical we always strive to educate our customers and communicate clearly. Here is a list of some common industry terminology and what they mean, so you can be fully informed and confident when discussing your upcoming project with any electrician.

• DNO: This stands for distribution network operator; they are the company that own the cables and substations linking you to the power plant where your electricity comes from. It is important to know the difference between the DNO and your supplier. Your supplier is the company who sends you your bills (EDF, Octopus, or EON to name a few). The DNO in our area is SSEN; there are different ones in different parts of the country.
• BS7671 (or just 7671): This is the British standard for electrical installations, also called the wiring regulations. All electricians have to sit an exam on this and should know it well.
• Consumer unit (or CU): This just means “fuse box”. It is a box where the big cables from your electricity meter are split up into smaller ones that go all around your building. Here you will also find all the protective devices keeping you safe!
• Distribution board (or DB): This is very similar to a consumer unit. There are a few small technical differences, although the terms are frequently interchanged. (CUs feed final circuits and DBs feed sub-mains if you are curious).
• Final circuit: This is the cable connecting your consumer unit to the load, like a kettle, light bulb, or oven. This is often used as part of "Ring final", this is the new term for ring main.
• Sub-main: These are big cables that feed a second consumer unit. For example, the cable from the DB in your house to your garage is a sub-main feeding another smaller consumer unit, which then feeds the final circuits in the garage like the lights or sockets.
• MCB: This stands for “miniature circuit breaker”. It is a device that goes in the CU or DB and acts as an over-current protection device, which stops the cable from getting hot and catching fire in the event of a fault or overload.
• RCD: This stands for “residual current device”. It is another device that goes in the CU or DB. It measures current leakage and will disconnect the circuit if the leakage is too high, hopefully stopping someone from being electrocuted if they accidentally touch something live.
• RCBO: This stands for residual current breaker with over-current. It combines the functions of the MCB and RCD into one device. These are very common on new installations.
• AFDD: This stands for arc fault detection device. These are not very common yet and are quite expensive. They use a small computer to detect the waveform caused by an arc and will disconnect the circuit to prevent a fire. They usually combine the functions of an RCD and MCB into one unit. The IET advises they should be fitted, but in most cases, it is not yet required. Ask an electrician for more information and whether you need them.
• SPD: This stands for surge protection device. They are similar to surge-protected extension cords but are installed in the CU to protect the entire house from transient overvoltage events that could damage electronic devices.
• BS3036 fuse (or rewireable fuse): These are an old type of fuse used from the 1960s to the 1980s. They feature a ceramic carrier where you thread a fuse wire. They are still approved and work fine, but they do not provide the same protection as modern equivalents. It is usually recommended to replace a re-wireable fuse-based CU.
• Twin: Short for twin and earth. It is the cable used in the vast majority of domestic wiring.
• Tri: Short for tri and earth, used mostly for multi-way switching on lights.
• Conduit: A special pipe (usually plastic or metal, e.g., PVC or steel) used to pull cables through.
• NYY (or NYYJ): A type of cable, often used for outside lights. NYYJ is a code describing the cable's construction, not an acronym.
• SWA: Stands for steel wire armour. Used for buried cables, such as outside lights or feeds for garages. It contains a steel armour for protection.
• AWA: Aluminium wire armour. Not used in domestic wiring. Similar to SWA but usually larger and used in industrial applications.
• H07 (H07RN-F): This is like the cable you would normally wire a plug to, but it is more durable and can have much larger cores in it, so can be used to power large loads.
• MICC (or MIMS): This stands for mineral insulated copper clad (or mineral insulated metal sheath). It is very fire resistant, so used in fire alarms, but expensive and hard to install, so is less common now.
• FP200: The replacement for MICC. Cheaper and easier to work with, used in most new installations.
• MWC: Minor Works Certificate. A document certifying that minor works have been carried out according to standards.
• Installation certificate: Required for major work, with test results and certifying that the work is compliant to applicable standards.
• EICR: Electrical Installation Condition Report. A report on the condition of your home's electrical system.
• C1, C2, C3, FI: EICR codes indicating hazard levels. C1 = immediate danger, C2 = potential danger, C3 = recommended upgrade, FI = further investigation needed.
• EDN: Electrical Danger Notice. This document is rarely issued. It says that the electrical system poses a serious, immediate, threat to life or property. This notice would often be the result of a customer refusing to have remedial work done. It is a waiver of liability from the electrican who issues it and protects them from legal action. If you receive one you should take immediate steps to have the problem rectified.