SOLAS Electrical Apprenticeship flashcards
SOLAS Electrical Apprenticeship · Build recall with a focused review session.
33 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Ohm's law
- For a resistive circuit, voltage equals current multiplied by resistance (V = I × R). This relationship allows any one quantity to be calculated when the other two are known.
- Power formula
- Electrical power equals voltage multiplied by current (P = V × I), and can also be written as I²R or V²/R. Power is measured in watts.
- Three-phase power
- For a balanced three-phase load, power equals √3 times line voltage times line current times power factor. The √3 factor arises from the 120-degree phase displacement.
- Star connection
- In a star-connected three-phase system, line voltage is √3 times phase voltage and line current equals phase current. A 400 V line supply gives 230 V per phase.
- Capacitive reactance
- Capacitive reactance equals 1 divided by (2π times frequency times capacitance). It falls as frequency rises, so a capacitor opposes low-frequency signals more than high-frequency ones.
- Transformer ratio
- The voltage ratio equals the turns ratio, and current ratio is the inverse. An ideal transformer conserves apparent power, so a voltage step-down produces a current step-up.
- Insulation resistance test
- Apply 500 V DC to a de-energised circuit with loads disconnected. A 230 V final circuit must read at least 1 MΩ to confirm the insulation is sound.
- Earth loop impedance
- Zs is the total resistance of the earth fault path, measured live. It must be low enough for the protective device to disconnect within the required time.
- RCD trip test
- A 30 mA RCD must trip within 300 ms at rated residual current and must not trip at 15 mA. The test button is a mechanical check only.
- Ring continuity test
- End-to-end resistance readings r1, rn and r2 are taken, then cross-connected. The highest socket readings should be about (r1+rn)/4 and (r1+r2)/4.
- Lock-off procedure
- Isolate the supply, prove dead with a voltage indicator checked on a known live source, apply a lock and warning notice, and keep the key with the worker.
- Periodic inspection
- An electrical installation condition report records the extent of sampling and the interval to the next inspection, which depends on the installation type and use.
- Design current Ib
- Ib is the current the circuit is expected to carry in normal use. The protective device rating In must be at least Ib, and cable capacity Iz at least In.
- Voltage drop limits
- Voltage drop must not exceed 3% of nominal voltage for lighting and 5% for other circuits on a public low-voltage supply. Calculate mV/A/m × Ib × length ÷ 1000.
- Correction factors
- Cable current-carrying capacity is adjusted by factors for ambient temperature (Ca), grouping (Cg), thermal insulation (Ci) and BS 3036 fuses (Cf).
- Ring final circuit
- A 32 A protected ring uses 2.5 mm² line and neutral conductors with a 1.5 mm² circuit protective conductor. The ring shares load between two paths.
- TN-C-S earthing
- In a TN-C-S (PME) system, the neutral and earth are combined in the supply and separated at the origin. The earth path relies on the supply neutral.
- TT earthing system
- A TT system uses a local earth electrode rather than a supply earth. Earth fault loop impedance is high, so a 30 mA RCD is normally required.
- Segregation of circuits
- Band I (SELV), band II (low voltage) and band III (telecoms) circuits are kept apart by separate compartments, barriers or spacing to prevent contact and interference.
- BS 7671 status
- The IET Wiring Regulations is the UK national standard for electrical installations. It is not a statute, but compliance is used as evidence of reasonable care.
- Disconnection times
- For a 230 V final circuit not exceeding 32 A, automatic disconnection must occur within 0.4 s. Distribution circuits are permitted 5 s.
- Basic protection
- Basic protection prevents contact with live parts in normal conditions, using insulation, barriers or enclosures. Fault protection deals with contact under fault conditions.
- Bathroom zones
- Zones 0, 1 and 2 define proximity to a bath or shower and restrict the equipment permitted in each. Supplementary bonding and 30 mA RCD protection are typically required.
- Minor works certificate
- A minor works certificate covers additions or alterations that do not include a new circuit. New circuits or consumer unit replacements need an electrical installation certificate.
- Silicon diode drop
- A forward-biased silicon diode conducts above about 0.7 V and blocks in reverse. The reverse breakdown voltage of the device must not be exceeded.
- Bridge rectifier
- A full-wave bridge rectifier produces two output pulses per input cycle, so ripple frequency is twice the supply frequency. A half-wave rectifier produces one.
- Zener diode
- A Zener diode operates in reverse breakdown to give a stable reference voltage. A series resistor limits the current through the Zener.
- Thyristor latching
- A thyristor turns on when a gate pulse arrives with the anode positive. It turns off only when anode current falls below the holding current.
- PLC scan cycle
- A PLC reads inputs, executes the program and updates outputs in a repeating scan. The scan time sets the response of the control system.
- PV cell voltage
- A photovoltaic cell produces about 0.5 to 0.6 V in open circuit. Cells in series raise voltage; cells in parallel raise current. Arrays are rated in kWp.
- Anti-islanding
- A grid-tied inverter must disconnect automatically when the grid supply is lost. This prevents the inverter from energising the network while workers expect it dead.
- MPPT
- Maximum power point tracking adjusts the array operating voltage to extract maximum power as irradiance and temperature change throughout the day.
- Wind power cube law
- Wind turbine power is proportional to the cube of wind speed and to the swept area. A small rise in wind speed produces a large rise in power.