Final answer:
Cables can be a fire and smoke hazard when an excessive electric current causes overheating. If the cables are not properly insulated, the excess heat can ignite nearby materials and start a fire, creating smoke.
Step-by-step explanation:
Cables can be a fire and smoke hazard due to the thermal effects of an excessive electric current. When an electric current passes through cables, it can cause overheating. If the cables are not properly insulated, this excess heat can ignite nearby materials and start a fire. The fire can then produce smoke, which can rapidly spread throughout a building, posing a danger to people inside.