Pancyprian Electrical Engineering III (Practical) flashcards
Pancyprian Electrical Engineering III (Practical) · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Let-go threshold
- The current at which a person can still release a gripped conductor, roughly 10 mA at 50 Hz; higher currents cause muscle contraction and prevent release.
- Hierarchy of control
- Order of risk reduction: eliminate the hazard, substitute, use engineering controls such as isolation, then administrative controls, with PPE as the last resort.
- Safe isolation procedure
- Identify the circuit, isolate, lock off and tag, prove the tester on a known source, prove dead at the point of work, then re-prove the tester.
- GS38 voltage indicator
- An approved voltage tester with fused or current-limited probes, finger guards and exposed tips no longer than 4 mm, proved before and after use.
- Ohm's law
- The relationship V = I × R, where voltage in volts equals current in amperes multiplied by resistance in ohms, valid for resistive circuits at constant temperature.
- Power factor
- The ratio of true power in watts to apparent power in volt-amperes, equal to cos φ, where φ is the phase angle between voltage and current.
- Parallel resistance
- The reciprocal of the total resistance equals the sum of the reciprocals of the branch resistances, so the total is always less than the smallest branch.
- Design current Ib
- The current the circuit is intended to carry in normal use, calculated from the load, and used to select the protective device rating In.
- Voltage drop formula
- For a single-phase circuit, Vd = (mV/A/m × Ib × L) / 1000, where mV/A/m is the tabulated value, Ib the design current and L the length in metres.
- Adiabatic equation
- The minimum protective conductor size S = √(I²t) / k, where I²t is the fault energy let-through and k depends on conductor material and insulation.
- BS 7671
- The IET Wiring Regulations, the technical standard for the design, installation and verification of electrical installations, currently the 18th Edition with Amendment 2.
- Minor Electrical Installation Works Certificate
- A certificate used for small alterations or additions to an existing installation that do not extend the existing certification, recording the work and test results.
- Competent person
- A person with sufficient technical knowledge, experience and skill to prevent danger and injury from the electrical work they undertake.
- Safe zone
- A permitted concealed cable route within 150 mm of a ceiling or corner, or aligned vertically or horizontally with an accessory, where cables are unlikely to be penetrated.
- Cable grouping factor
- A correction factor Cg applied when cables are bunched or enclosed, reducing the current-carrying capacity because heat cannot dissipate as freely.
- MCB Type B
- A miniature circuit breaker that trips between 3 and 5 times its rated current, suitable for resistive loads with low inrush current.
- RCD additional protection
- A 30 mA residual current device that provides additional protection against electric shock but does not replace basic or fault protection.
- Breaking capacity Icn
- The maximum prospective short-circuit current a protective device can safely interrupt without damage, which must not be less than the fault level at its position.
- TN-C-S system
- An earthing arrangement where the neutral and protective earth are combined in the supply and separated at the origin, also known as protective multiple earthing.
- Main protective bonding
- The connection of extraneous conductive parts such as gas and water pipes to the main earthing terminal, using a conductor of at least 10 mm².
- Earth fault loop impedance
- The total impedance of the path taken by fault current from the origin through the live conductor, the fault and back via the protective conductor and earth.
- Insulation resistance test
- A dead test at 500 V DC between live conductors and earth, with a minimum acceptable value of 1 MΩ for a 230 V circuit.
- Ring final circuit test
- End-to-end resistance measurements of line, neutral and CPC, where the CPC reading is about 1.67 times the line reading for 2.5/1.5 mm² cable.
- RCD trip time
- At rated residual current the device must trip within 300 ms; at five times rated current within 40 ms for a 30 mA device.
- Earth fault loop impedance test
- A live test measuring Zs at the furthest point of a circuit, which must not exceed the maximum value for the protective device to disconnect within the required time.
- N-E fault
- A connection between neutral and earth, often caused by moisture or damage, which causes an RCD to trip because current bypasses the sensing coil.
- Thermal imaging
- A diagnostic technique using an infrared camera to detect hot terminals, overloaded conductors and loose connections before they fail or cause fire.
- Split-load consumer unit
- A board with circuits divided so that socket outlets are protected by a 30 mA RCD while lighting and other circuits remain on a separate section.
- Main switch
- The device at the origin of an installation that isolates both line and neutral, allowing the consumer unit to be made dead for maintenance.
- Overload relay
- A protective device in a motor circuit that detects sustained overcurrent and trips the contactor, protecting the motor from overheating.
- Terminal torque
- The tightening force specified by the manufacturer for a terminal screw, which ensures a low-resistance connection and prevents loosening under thermal cycling.
- Cable gland
- A fitting that secures a cable at its entry to an enclosure, provides strain relief and maintains the ingress protection rating of the enclosure.