Section E3605 of the IRC Part E (Electrical) establishes requirements for wiring methods in residential buildings. Nonmetallic sheathed cable (Romex) is the most common wiring method in residential construction. Romex consists of copper conductors insulated with rubber or plastic, contained within a plastic sheathing. Cable is typically 14/2 (two 14-gauge conductors plus ground) or 12/2 for 20-amp circuits. Romex must be secured to framing with staples spaced no more than 4.5 feet apart and within 12 inches of boxes. Romex must not be installed in attics except along framing members. Cable must be protected where it passes through walls, typically with PVC sleeves in wood frame construction. Electrical metallic tubing (EMT or conduit) is required in certain locations including wet locations and where physical protection is needed. Conduit must be sized based on the number and size of wires it contains. Flexible metallic conduit may be used for final connections to equipment. Knob-and-tube wiring, an older method with individual conductors, is prohibited in new construction. Aluminum conductors are prohibited in new residential wiring. Circuit breakers must be sized to match the wire gauge, with 15-amp breakers for 14-gauge wire and 20-amp breakers for 12-gauge wire. Grounding is required for all circuits, with a ground conductor running from the circuit breaker through the wiring to every outlet and back to the service entrance.