Reference guides
Practical briefs on the information electrical design and testing need. Explore the principles and the information behind each topic.
Cable & installation
Cable sizing
Cable size is a circuit design decision. A current value and a cable length do not describe all the conditions a cable will operate in.
Ring final circuits
A ring final circuit has two paths from the protective device to its loads. Its design and verification depend on the continuity and arrangement of the actual circuit.
Cable tray and trunking
Containment needs to accommodate cables physically and support their installation conditions. Space, loading and thermal effects are separate checks.
Voltage drop
Voltage drop is the reduction in voltage along a loaded circuit. A useful calculation must represent the actual cable, supply and operating conditions.
Three-phase cable design
Three-phase cable selection needs the load on each conductor, the cable arrangement and the installation conditions.
Conduit capacity
Installing cables in conduit involves physical capacity, pulling conditions and thermal performance.
SWA cable selection
Steel wire armoured cable design depends on its construction, installation conditions and the intended earthing arrangement.
Electric shower circuits
A shower circuit must be designed for the particular shower and the complete route to it.
Cooker circuit design
Cooking equipment varies in power, controls and connection requirements. The circuit needs to match the actual equipment and use.
Lighting circuit design
Lighting circuits must account for the actual fittings, controls and electrical characteristics.
SWA cable glands
A suitable gland must match the specific cable construction and the environment of the termination.
Hot tub electrical supplies
A hot tub supply requires a design based on the equipment, its location and the existing installation.
Fire alarm cabling
Fire alarm cable selection depends on the system design and the performance required from its circuits.
Immersion heater circuits
An immersion heater circuit must match the appliance and installation conditions.
Planning cable quantities
Ordering cable starts with the designed routes and the specified cable types.
AWG and metric conductors
AWG and square millimetres describe conductor size using different systems. Similar nominal sizes are not automatic installation substitutes.
Testing & protection
Prospective fault current
Prospective fault current describes the current that could flow under a fault. It informs equipment selection, but a voltage divided by an assumed impedance is not a site verification.
Maximum Zs values
Zs is earth-fault loop impedance. The applicable limit depends on the protective device, the required disconnection conditions and the basis of the comparison.
R1 + R2 resistance
R1 + R2 combines the resistance of the circuit line conductor and its protective conductor. Predicted and measured values have different evidential roles.
Earthing and bonding
Earthing, protective conductors and protective bonding perform related but distinct functions. Their selection requires the actual supply and installation conditions.
Circuit breaker selection
A breaker’s current rating is one part of its specification. Selection must also account for fault interruption and the characteristics of the connected circuit.
Earth-fault loop impedance
The earth-fault loop includes the supply and the circuit fault-return path. Both the model and the measurement method matter.
RCD selection
Residual current device selection depends on the residual-current waveforms and the circuit’s intended protective function.
Protective-device coordination
Coordination concerns how protective devices operate together for the possible overload and fault conditions.
Interpreting electrical test results
Electrical test results need to be interpreted alongside the installation, inspection findings and the test method.
Design & planning
Diversity and demand
Diversity recognises that connected loads may not all operate at their full ratings simultaneously. Its application depends on the installation and expected use.
Electrical load assessment
Adding nameplate ratings gives a connected load. Determining the current and demand of an installation needs more information about the loads and how they operate.
Motor circuits
Motor input current, starting behaviour and protection depend on the motor and its method of control.
Maximum demand
Maximum demand is the anticipated coincident demand of an installation under its intended operating conditions.
Three-phase load balancing
Balancing a load schedule means considering individual phase demand as well as the total installation load.
EV charging circuit design
An EV charger adds a sustained and potentially managed load with installation-specific protection requirements.
Consumer unit planning
A consumer unit needs to accommodate the installation’s protection arrangement and circuit schedule.
Power factor correction
Power factor correction needs to account for the load profile, the supply and any harmonics.
Emergency lighting design
Emergency lighting design is concerned with illumination in the actual space during a supply failure.
Generator sizing
Generator selection must account for transient behaviour and the way loads are connected.
UPS selection and runtime
A UPS must satisfy output-power requirements and deliver the required runtime under the actual load.
Transformers and busbars
Transformer and busbar selection brings together load capacity, fault withstand and installation conditions.
Solar installation planning
Solar output depends on the site and system, while electrical design depends on the selected equipment and connections.
Heat pump electrical planning
A heat pump’s heat output is different from its electrical input, and both vary with operating conditions.
Smart home electrical loads
Connected controls can change when equipment runs, but their presence does not automatically reduce design demand.
Network connection applications
The applicable network connection process depends on the installation and the distribution network operator.
Electrical installation estimates
An installation quote needs a defined scope and current prices for the actual work.