Types of Cables

Three Wiring Systems Three systems of wiring used in most installations: 1.) Non-metallic sheathed cable 2.) Armored cable 3.) Conduit

Non-Metallic Sheathed Cable Copper or aluminum wires covered with paper and vinyl for insulation and protection Some non-metallic sheathed cable are waterproof and suitable for burial in soil

Armored Cable Consists of a flexible metal sheath with individual wires inside The wires are insulated with vinyl and wrapped in paper for protection Armored cable provides good protection against mechanical damage It is fairly easy to install in narrow and irregular building sections Does have a tendency to rust and develop short circuits which makes it unsuitable for use in damp areas

Conduit Tubing that contains individual insulated wires 1/2”, ¾”, 1” or larger in diameter May be rigid or bendable Available in metal or plastic

Electrical Metallic Tube (EMT) Special benders permit shaping EMT in bends of up to 90 degrees Couplings and connectors are used to assemble conduit and attach Waterproof plastic fittings provide waterproof seals where needed for metal conduit Conduit systems are used to provide the most common protection for wiring and are required for most commercial jobs

Wire Type and Size Individual wires within cable or conduit may be aluminum or copper Smaller sizes include No.14 wire for 15amp circuits, No 12 for 20amp circuits, and No. 10 for 30amp 120 volt circuits Ampere ratings apply to copper wire For aluminum, it is necessary to use one wire size larger than is specified for copper wire Wire size is designated by gauge or AWG (American Wire Gauge) The lower the gauge number, the larger the wire size

Strands Strands are placed together to form bundles for wire sizes No.8 and larger in order to improve flexibility and conductivity Electricity is carried on the outer surfaces of wire Stranded wire has more total surface area than solid wire of equal diameter and carries more current Either solid wire or stranded wire may be placed in cables or conduits

Voltage Drop Refers to a loss of voltage as it travels along a wire Causes lights to dim, heaters to put out less heat, and motors to put out less power and to overheat The larger the wire, the less problem there is with voltage drop for a given amount of current Longer wire = greater problems

Wire Identification Outer covering Individual wire covering Cable construction Number of wires All of these items determine where a cable can be used

Wire Identification Cont’d Wire type is stamped on the outer surface of the wire or cable or cable covering *Common types of wire & cable: Type T – for use in dry locations Type TW – for use in dry or wet locations Type THHN – for use in dry locations with high temperature Type THW and THWN – for use in wet locations with high temperature Type XHHW – for high moisture and heat resistance Type UF – for direct burial in soil but not concrete

Wire Identification Cont’d Individual wires are color coded to help identify their function in the circuit Black wires, red wires, and blue wires are positive (hot) wires Carries current to appliances White wires = neutral wires Carries current from appliance back to the source Green wires and bare wires are used to ground all metal boxes and appliances in the circuit

Nonmetallic Sheathed Cables 12-2: two strands of No.12 wire, one black and one white 12-2w/g: two strands of No. 12 wire plus a ground wire (w/g means “with ground”), one black, one white, and one green or bare 12-3: three strands of No.12 wire, probably, one black, one red or blue, and one white 12-3w/g: same as 12-3 cable with the addition of a green or bare wire for grounding the circuit