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John Watson Electrical Services |
Electrical Terms and Glossary The electrical world is quite full of `TLA's
- Three letter abbreviations. Click on the following sub-titles to take
you down the list below... TLA Three Letter Abbreviations. Some in the computing world are even abbreviations of other abbreviations! BSc Batchelor of Science - University degree qualification (I have one in Electrical and Electronic Engineering), Others are BA - Batchelor of Arts, BEng - Batchelor of Engineering, or MSc etc. where the M is for Master. Electrical Trade Associations etc IEE
Institution of Electrical Engineers - Long
established trade association for professional electrical / electronic engineers.
Publishers of the IEE wiring regulations. MIEE
A person who is a Full Member of IEE - not a company but
individuals. CEng
A person who is a Chartered Engineer and member of the Engineering Council. I am. JIB
Joint Industry Board (Joint venture between ECA (Electrical Contractors Association) and
Amicus) NICEIC
National Inspection Council for Electrical Installation Contracting - Independent trade association for electrical contractors.
Larger
electrical contracting companies are often members. Membership applies to the
company not the individuals. ECA
Electrical Contractor's Association - Independent trade association for electrical contractors.
Larger
electrical contracting companies are often members. Membership applies to the
company not the individuals. BABT British Approvals Board for Telecommunications. Approval mark for telephones etc. for use in the UK. BASEC British Approvals Services for Cables. BEAB British Electro technical Approvals Board. Approval body for approving electrical appliances for use in the UK. Back to Top Electrical Units V
Volts - unit of
electrical voltage or potential difference to be precise. * A word of explanation - the present-day
"declared" mains voltage in UK is now 230V, as opposed to 240V. This
is due to European harmonisation. A (or Amperes to be precise). Unit of electrical current. That is how much electricity is being used by an appliance. Fuses are always rated by current as are cables. Typical current values for appliances in houses range from 0.1A to 45A. Electrical power is defined as Voltage x Current. For mains use the voltage is usually (more or less) constant. Also in widespread use in electronics is the term mA - milli Amps. There are 1000 mA in 1Amp. Ohms
Unit of electrical resistance. Every electric cable, wire and PCB track has resistance, which causes
heating effects when a current passes through it. So the larger the
current, the larger the cable size in order that the resistance is
lower, hence the heating effect is kept within acceptable limits. Cable length also
plays a part too.
Typical circuit resistance values are less than one ohm for domestic
electrical cables. This is why kettles have a thicker cable than
table lamps. kWh
Kilo-Watt Hour. Measure of energy used - electrical in this example.
Your home electricity meter measures in these units. One unit costs about 5
pence. W
or kW is a measure of electrical power. 1000W = 1 kW.
For example, a 100W light bulb will consume 1kWh of energy in 10 hours. Back to Top Electrical Terms AC Alternating current. The type of electricity normally used in houses. Called alternating because is has a cyclical current waveform that alternates as the generator in the power station rotates, at 50 times per second. NOTE: When we refer to 230V ac mains voltage in the UK, this is not the peak value. The peak voltage in the cycle is 340V - the 230V is the RMS - or Root Mean Square (now were getting too complicated for this guide). See below for further complications - single or three phase. DC Direct current. Does not alternate! Normally used in electronic circuits and computers etc and is often derived from ac-mains via a power supply. All batteries are DC. Cars, lorries etc. run on DC battery power, as do touring caravans and boats - some may also have ac power via a generator or external mains hook-up. A device called an inverter can be used to create ac at mains voltage from dc battery power. These are used in computer UPS units. Single-Phase
Or Three-Phase. I
am often asked the difference between three-phase and single phase. A lot of
people think they are very different, because one is called 230V, and the
other 400V. However they are almost the same thing - single phase is simply one
of the phases of three-phase, together with a neutral. Phase Rotation Related to three phase, above. This is very important and often overlooked. For example, if someone is wiring up a three phase socket, they could inadvertently swap over two of the phases and all would seem well - voltages etc. would all be OK. However, connect a three-phase motor, and it will run the wrong way if the phases are reversed. This could lead to some dangerous situations. What is important is the order the phases, or what is known as "phase rotation". There are instruments that can measure this. I have one which is part of my earth loop tester. RCD
Residual Current Device - affords extra protection
against electric shock, now mandatory in some installations MCB Miniature Circuit Breaker - Modern replacement for fuses in consumer units (fuse boxes). Has benefit of more precise tripping and can be reset. In my opinion all fuse boxes and consumer units that still have fuses should be converted to use these. RCBO Residual Current Breaker with Overload protection. Combined functions of MCB and RCD in one unit. Used to protect the particular circuit and preferable to separate RCD and MCBs. Recommended for commercial installations and especially on ring circuits where there are lots of computers in use (as opposed to a single RCD for the whole building). Back to Top FCU
Fused Connection Unit - commonly used in kitchens to
connect fixed appliances to the ring main. Also SFCU which is an FCU with a
switch - usually double pole so isolates both live and neutral to the appliance
- but NOT the earth. Also commonly referred to as fused Spurs EMC Electro Magnetic Compatibility - A complex subject that is usually referred to in the context of ensuring equipment is not adversely affected by electrical noise eg. from welding equipment, and that equipment does not give out excessive electrical noise/ interference, in-order to prevent audible hiss or crackle through radios etc.. CE marking covers EMC compliance, amongst other requirements. CE
Commonly referred to as CE marking on products. Stands for Conformity
Europene - a PAT
Portable Appliance Testing. Periodic inspection and testing of portable appliances for electrical safety and
maintenance. Required for commercial premises under Electricity at Work Act and
recommended for domestic ones too. We also recommend ALL electrical equipment should
be checked periodically, not just portable equipment. PC
Personal Computer. Can also refer (in industrial electrics) to Programmable Controller or PLC - Programmable Logic Controller. Earthing
Method of connecting most exposed metal work in a building and metal appliances
to electrical Earth - nominally 0V. Windows and shelves are normally excluded
but most metal pipes etc. are included. This means that in the event of a fault
- eg. Live wire touching a metal case, then the earth will facilitate automatic disconnection of the mains supply (known as
EEBADS *
in the trade). This should
cause the circuit protective device - fuse to blow, or MCB to trip. Country
properties often have an Earthing rod to provide some protection - usually with
an RCD as well. PME
Protective Multiple Earthing - commonly used in this area for new buildings.
Only the Live and Neutral (or to be precise the PEN conductor) conductors enter
the building, and the
Neutral and Earth are joined just after they enter the building. Inside the building
they are separate. This gives faster blowing of fuses etc. in event of a
fault - but is not entirely without its drawbacks. Back to Top Ceiling Rose No, not a plant, but an innocent looking round thing on the ceiling above conventional lights. Complex inside as they usually act as a junction box for 11 or more conductors (wires). Can be daunting to replace - even for skilled people, especially if other electrical cables have been added in as well. Watch out for the switched live, is my tip on this one. Architrave Switch Small thin light switch that is often fitted onto Architrave - which is?... The curvy frame or moulding found around a door frame, that traditionally covers the joint between the wall-plaster and the door frame itself. CCTV Closed Circuit Television - commonly refers to security cameras, that record on to a tape and/or monitored by a control centre. BS British Standard C&G City and Guilds - body that set exams for electrical trainees and many other trades. CIS
Construction Industry Scheme. Inland Revenue scheme that applies to
self-employed persons (like me) who do work in the construction industry. Identifies
who the person is, by means of a photo card, and allows tax deduction at source
for construction projects where the person is working for a main contractor. HiFi
- Stands for "High Fidelity". A term used to describe good quality
sound systems. Although rather distorted (a pun!) from what it meant some years
ago, it now often applies to any type of music system - some that are distinctly
Low-Fi to my ears. Back to Top Electrical Inspection and Test Terms Ze - Earth fault loop impedance, as measured at the origin of the installation - usually at the meter or consumer unit for domestic properties. Measured in Ohms. Explanation of Earth fault loop impedance is beyond the scope of these notes. Generally, the lower the reading the better. Zs - Earth fault loop impedance, at a particular point in an installation. Measured in Ohms. PFC - Prospective Fault Current. The maximum current for a fault between phases, between live and neutral or between phase and earth that the supply can provide. Usually measured by a special instrument at the supply origin - usually at the meter or consumer unit for domestic properties. Measured in kA (kilo Amps or Amps x 1000). PSCC - Prospective Short Circuit Current. The maximum current between phase and neutral, or between phases that the supply can provide. Usually measured by a special instrument at the supply origin - usually at the meter or consumer unit for domestic properties. Measured in kA (kilo Amps or Amps x 1000).
microCHP
small Combined Heat and Power (plant). In my opinion, this is the future of heating and electricity
generation. PIR - Passive Infra Red. The name of the technology commonly used for movement sensors in intruder alarms and for outdoor security lights. Works by detecting the movement of heated object in its field of "vision". DAB - Digital Audio Broadcasting, as in DAB digital radio. HD - High Definition, as used to describe new style TV system which uses a lot more lines/dots that the present system "PAL" system.
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