gh-ctvet-cert-ii-electrical cheat sheet

Lockout/tagout (LOTO) sequence: isolate the source, release stored energy (capacitors, springs, pneumatics), verify de-energisation with a proven tester, then apply personal locks and tags; only the person who applied a lock removes it.

Hierarchy of control, most to least effective: elimination, substitution, engineering controls, administrative controls, then PPE.

Electric shock severity depends on current path and duration; roughly 1 mA is perception threshold, 10-30 mA causes muscle tetanus (cannot let go), and 30 mA or more through the chest can cause ventricular fibrillation.

Body resistance falls sharply when skin is wet or broken, so touch voltage limits (commonly 50 V AC / 120 V DC for dry locations) are set well below dangerous levels.

Arc flash: use PPE rated to the incident energy category; working distance, available fault current and clearing time determine incident energy, so never assume a panel is low-risk without a label.

Temporary earthing/grounding clamps must be applied with a rated earth-and-test device and rated for the prospective fault current and duration.

A confined space entry requires atmosphere testing (oxygen, flammable gas, toxic gas), a rescue plan, an attendant, and continuous ventilation before entry.

First aid for electric shock: isolate supply before touching the casualty, call emergency services, start CPR if breathing/ pulse absent, and treat burns with sterile non-adherent dressing.

Waste segregation applies to lamps (mercury), batteries, cable sheathings and solvents; these are hazardous waste and must go to licensed disposal streams.

Ohm's law: V = I × R; power: P = V × I = I²R = V²/R.

Series circuit: same current through all elements; R_total = R1 + R2 + ...; voltage divides in proportion to resistance.

Parallel circuit: same voltage across all branches; 1/R_total = 1/R1 + 1/R2 + ...; current divides inversely with resistance.

Kirchhoff's laws: sum of currents at a node is zero (KCL); sum of voltages around a closed loop is zero (KVL).

AC impedance: Z = √(R² + (X_L − X_C)²); X_L = 2πfL, X_C = 1/(2πfC); resonance when X_L = X_C.

Power factor: PF = P/S = cos φ; true power P in watts, apparent power S in VA, reactive power Q in var; S = √(P² + Q²).

Three-phase: line voltage = √3 × phase voltage in star; line current = √3 × phase current in delta; total power P = √3 × V_L × I_L × PF.

Transformer and motor relationships: V1/V2 = N1/N2; synchronous speed N_s = 120f/P (rpm).

Cable voltage drop (single-phase) ≈ 2 × I × L × (R cos φ + X sin φ), with L in km and R, X in Ω/km.

Copper: conductivity ≈ 58 MS/m, low resistivity (~1.72 × 10⁻⁸ Ω·m at 20 °C); aluminium is ~61% as conductive by volume but ~30% lighter, so larger cross-sections are needed.

Conductor resistance rises with temperature: R_t = R_20 × [1 + α(t − 20)], with α ≈ 0.00393 /K for copper.

Insulation classes and maximum conductor temperatures: PVC 70 °C, XLPE 90 °C, EPR 90 °C, silicone rubber 180 °C, mineral (MI) up to 250 °C.

Cable designation decodes construction: e.g. PVC/SWA/PVC means PVC-insulated, steel wire armoured, PVC-sheathed; armouring provides mechanical protection and an earth path.

Cross-linked polyethylene (XLPE) offers higher current rating and better dielectric strength than PVC at the same size.

Ferromagnetic core materials (silicon steel laminations) reduce eddy-current and hysteresis losses in transformers and machines.

Contact materials use silver alloys for low contact resistance and resistance to arcing; silver-cadmium and silver-tin oxide resist welding under fault currents.

Cable insulation resistance falls with moisture ingress and thermal ageing, so IR tests are a key condition indicator.

Voltage tester (two-pole or proving unit) is the only acceptable device to prove dead; a multimeter alone is not a safe isolation verifier.

Insulation resistance tester applies 250/500/1000 V DC; minimum acceptable IR for a 230/400 V installation is typically 1 MΩ (commonly ≥ 1 MΩ per BS 7671, with 1 MΩ per circuit as a practical floor).

Continuity tester: low-resistance ohmmeter with a test current of at least 200 mA for protective conductor continuity verification.

Earth loop impedance tester measures Zs; RCD tester measures trip time at IΔn and 5×IΔn and verifies no trip at ½IΔn.

Clamp meter measures current without breaking the circuit; it must be used on a single conductor, or the reading will be zero on a two-wire cable.

Insulated tools must be rated 1000 V and inspected for damage before every use; damaged insulation is removed from service.

Torque wrench: terminal screws must be tightened to the manufacturer's specified torque; under-torque causes hot joints, over-torque damages strands.

Cable pulling: use a stockinette, cable roller and lubricant; never exceed the manufacturer's minimum bend radius (typically 8× cable diameter for armoured, 6× for flexible).

Cable current-carrying capacity (Iz) must satisfy Iz ≥ In ≥ Ib, where Ib is design current and In is the protective device rating.

Correction factors: Iz = It × Ca × Cg × Ci, where Ca is ambient temperature, Cg is grouping, Ci is thermal insulation; all apply simultaneously.

Protective conductor sizing: for phase conductors ≤ 16 mm², the PE is the same size; for 16-35 mm², PE is 16 mm²; above 35 mm², PE is half the phase cross-section.

Bend radius and support: cables must be supported at intervals (typically 300-400 mm horizontal for sheathed cable) and protected against abrasion.

Segregation: power and data/telecom cables must be separated (typically ≥ 50 mm or by a barrier) to limit electromagnetic interference.

Socket outlet circuits in domestic installations are commonly 2.5 mm² on a 16 A or 20 A breaker; lighting 1.5 mm² on 10 A.

Cable derating in thermal insulation requires reference to the installation method (clipped direct, in conduit, in wall) and the appropriate table in the standard.

Fire-rated cable (e.g. mineral-insulated or enhanced) is required for life-safety circuits such as fire alarms, emergency lighting and smoke extraction.

DC machines: shunt (separately excited) is used for constant-speed drives; series has high starting torque but must never run unloaded; compound combines both.

Induction motor slip: s = (N_s − N_r)/N_s; at no load slip is near zero, at full load typically 2-5%.

Starting methods for induction motors: direct-on-line (DOL) for small motors, star-delta (reduces starting current to 1/3), soft starter, and variable-frequency drive (VFD).

VFD: changes frequency and voltage to control speed; below base speed constant V/f maintains flux; above base speed field weakening reduces torque.

Transformer losses: copper (I²R) losses vary with load squared; iron (core) losses are essentially constant at rated voltage and frequency.

Transformer efficiency is maximum when copper loss equals iron loss; transformers are rated in kVA because heating depends on voltage and current, not load power factor.

Motor protection: thermal overload relay protects against sustained overload; it does not protect against short circuit, so a short-circuit protective device is also required.

Single-phase motors: capacitor-start for high starting torque, permanent-split capacitor for quieter running, shaded-pole for small fans.

Earthing system types: TN-S (separate PE), TN-C-S (combined PEN split at origin), TN-C (combined throughout), TT (local earth electrode), IT (isolated or high-impedance earth).

TN systems rely on the metallic return path for fault current; TT systems require an RCD because the earth loop impedance is too high to operate an overcurrent device quickly.

Disconnection times: 0.4 s for final circuits ≤ 32 A in TN, 5 s for distribution circuits; TT requires RCD ≤ 1 s at 230 V.

RCD types: AC (sinusoidal residual current only), A (also pulsating DC), B (also smooth DC), and selective (S) for time delay.

Earth electrode resistance: Ra × IΔn ≤ 50 V for TT systems, so a 30 mA RCD needs Ra ≤ 1667 Ω (commonly designed to ≤ 200 Ω for stability).

Fault finding sequence: verify supply, isolate, test insulation resistance, then continuity, then polarity, then loop impedance, then RCD function.

A high Zs reading indicates a poor earth path - check the main earthing terminal, bonding, and the protective conductor connections before assuming a cable fault.

Short-circuit vs overload: short circuit is a low-impedance fault with very high current; overload is a sustained current above design current but within the circuit's capability.

Drawing types: block diagram (function), schematic/circuit diagram (electrical function, no physical layout), wiring diagram (physical connections), and layout/installation drawing (positions on site).

Standard symbols: IEC 60617 for graphical symbols; BS EN 61082 for documentation; IEC 81346 for reference designation.

Single-line diagram (SLD) shows the distribution hierarchy from origin to final circuits, with device ratings and cable sizes.

Cable schedule lists circuit reference, cable type/size, length, origin and destination - essential for installation and testing.

As-built drawings must reflect the installed system; any deviation from the design must be recorded and signed off.

Test certificates and schedules of results (e.g. insulation resistance, continuity, Zs, RCD times) form part of the handover documentation.

Polarity and phase rotation must be verified against the drawing; a reversed phase can destroy three-phase motors.

Revision control: drawings carry a revision number/letter and date; superseded drawings must be withdrawn from site to prevent rework.

Regulatory framework: electrical work must comply with the national wiring standard (e.g. BS 7671 / IEC 60364) and local building regulations; notifiable work requires certification by a competent person.

Competence is defined by qualification, experience and continuing professional development (CPD); records of CPD support registration and licensing.

Contract essentials: scope, price, payment terms, programme, variations procedure, and dispute resolution must be agreed in writing before work starts.

Estimating: labour cost = hours × hourly rate; add materials with wastage (typically 5-10%), overheads, profit margin and contingency.

Cash flow management: invoice on milestones, track retention, and maintain a contingency for variations and defects liability.

Health and safety duties: risk assessment before work, method statements for high-risk tasks, and incident reporting to the regulator.

Client communication: document changes and instructions in writing; verbal agreements should be confirmed by email to avoid disputes.

Business sustainability: maintain insurance (public liability, professional indemnity), warranties, and a documented quality management process.

Business structures: sole trader (unlimited liability), partnership, and limited company (separate legal entity, limited liability).

Pricing strategy: cost-plus (cost + markup), competitive (market rate), and value-based (price reflects client benefit).

Marketing for electrical contractors: local reputation, referrals, online presence, and accreditation logos build trust.

Employment law: contracts must state pay, hours, holiday, notice, and grievance procedures; discrimination and harassment are prohibited.

Apprenticeship and training: structured on-the-job training plus off-the-job learning leads to recognised qualifications.

Record keeping: keep invoices, receipts, test certificates, and timesheets for the statutory retention period (commonly 6 years).

Risk management: identify, assess, control and review risks; maintain a risk register for projects.

Customer service: clear quotes, punctuality, tidy work, and a documented complaints procedure improve retention and referrals.

Schematic vs wiring diagram: a schematic shows function and logical connections; a wiring diagram shows terminal numbers and physical routing.

Reference designations (IEC 81346): = for function, - for location, + for product; e.g. -Q1 is a circuit breaker.

Cable core identification: brown (L1), black (L2), grey (L3), blue (N), green/yellow (PE) in harmonised European cables.

Terminal numbering on contactors and relays follows IEC 60947: A1/A2 coil, 13/14 normally open, 21/22 normally closed.

Motor starter drawings show main circuit (L1-L2-L3 to motor) and control circuit (coil, auxiliary contacts, overload).

Documentation package: drawings, cable schedules, test certificates, operation and maintenance manuals, and as-built records.

Version control: each drawing has a unique number, revision, date, and approval signature; changes are logged in a revision table.

Digital documentation: BIM and CAD files must match the as-built installation and be handed over in the agreed format.

Professional ethics: honesty in testing and certification, no falsified results, and disclosure of conflicts of interest.

Continuing professional development: at least 30 hours per year is a common benchmark for maintaining registration.

Insurance: public liability (typically ≥ £2 million), employer's liability (legally required), and professional indemnity for design work.

Contracts: use standard forms (e.g. JCT or NEC) for larger projects; for small works, a written quotation with terms and conditions is sufficient.

Payment: agree payment terms (e.g. 30 days), issue invoices promptly, and follow up overdue accounts with a formal reminder.

Dispute resolution: negotiation, mediation, adjudication, arbitration, litigation - in increasing cost and formality.

Business planning: market analysis, target customers, pricing, cash flow forecast, and break-even analysis.

Employability: a CV should highlight qualifications, practical experience, and safety record; a portfolio of completed work supports job applications.

Break-even point = fixed costs / (selling price per unit − variable cost per unit).

Gross profit = revenue − cost of goods sold; net profit = gross profit − overheads.

Markup vs margin: markup is on cost, margin is on selling price; 25% markup ≈ 20% margin.

Quotation vs estimate: a quotation is a fixed offer; an estimate is an approximation and is not legally binding in the same way.

Retention: commonly 5% withheld until practical completion, with half released at completion and half after the defects liability period.

Variations must be priced and agreed before execution; unsigned variations are a common source of disputes.

Health and safety policy: written policy required for employers with five or more employees.

Environmental responsibility: waste segregation, energy-efficient lighting design, and compliance with WEEE and RoHS.

Time management: use a work breakdown structure to estimate durations; critical path identifies the longest sequence of dependent tasks.

Quality assurance: inspection and test plans (ITP) define hold points and witness points for verification.

Supply chain: vet subcontractors for competence, insurance and safety record before appointment.

Customer complaints: acknowledge within 24 hours, investigate, respond in writing, and record corrective action.

Digital tools: estimating software, project management apps, and cloud storage for certificates improve efficiency and traceability.

Networking: trade associations, professional institutions, and local business groups generate referrals and keep skills current.

Financial records: separate business and personal accounts; use accounting software for VAT and tax returns.

Succession planning: document processes and train successors to maintain business continuity.

Regulatory compliance: keep up to date with amendments to the wiring standard and building regulations; ignorance is not a defence.

Competence: only undertake work within your competence; seek specialist advice for unfamiliar systems.

Documentation: every job should have a quote, a risk assessment, a test certificate, and an invoice.

Insurance claims: notify the insurer promptly, preserve evidence, and cooperate with the loss adjuster.

Business growth: reinvest profit, diversify services (e.g. EV charging, solar PV), and build a skilled team.

Customer retention: follow up after completion, offer maintenance contracts, and request reviews.

Ethical marketing: do not claim accreditation you do not hold; verify logos and registration numbers.

Personal development: set SMART goals, seek feedback, and review progress quarterly.