Electrical Materials
What this domain tests
Electrical Materials tests selection of conductors, insulation, enclosures and consumables by electrical, thermal, mechanical and environmental suitability.
Core rules
- Copper has high conductivity and good mechanical strength; aluminium is lighter and cheaper but has lower conductivity and forms an oxide film, so it needs suitable terminals and jointing compound.
- PVC is the common insulation for domestic wires, typically rated 70 °C; heat-resistant PVC or XLPE is used near heaters and in hot locations.
- Porcelain and bakelite are rigid insulators: porcelain for fuse carriers and insulators, bakelite for switch covers and socket bodies.
- GI conduit resists rust; MS boxes and conduit need painting or enamelling. Plastic conduit is used in concealed wiring but must be rated for the environment.
- Solder for electrical joints is commonly 60/40 tin-lead with rosin flux; flux must not be left on terminals because it can corrode.
- Insulating tape must be PVC, applied in overlapping layers, and never used as the only insulation on a joint that needs a box.
Worked example
A 16 A socket circuit in a shop needs a conductor. A 2.5 mm² copper PVC-insulated wire is selected because it carries the load with acceptable voltage drop and is easy to terminate. Aluminium of the same size would carry less current and needs a bimetallic connector if joined to copper.
Traps that cost marks
Joining copper and aluminium directly without a suitable connector; using ordinary PVC tape near a hot appliance; selecting a material by price alone; and forgetting that metal conduit and boxes must be earthed.