Wire and Cable Buying Guide | Knoweasy Electrician Guide - knoweasy

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Wire and Cable Buying Guide | Knoweasy Electrician Guide

October 11, 2022


Nearly 2 miles of cable runs through the average home. Although you've never seen most house wiring, it powers everything and it's helpful to be able to identify its purpose.


The basics


I. Understanding the difference between wire and cable.


  • A wire is a conductor that carries current through a circuit.
  • A cable is a group of wires that are sleeved together.
  • Most conductors are copper, which is corrosion-resistant and better than aluminum. Aluminum is a cheaper, lighter-weight alternative.

The American Wire Gauge (AWG) system provides standard wire gauge sizes. The higher the gauge number, the smaller the size of the wire. For an example, see the AWG chart below. The National Electrical Code (NEC) specifies the wire and cable that can be used for electrical applications.


Key definitions


Amperage: the measured value of current

Voltage: The difference in potential between two points

Voltage drop: the difference between the measured values at each terminal of the device

Wattage: how much electrical energy is used


How to identify wire and cable


A 250-foot roll of Southwire jacketed wire.

Information is printed on each jacket to help you select the correct product for your job. The letter code provides the properties of the wire, as well as the material, gauge and voltage rating.


Naming and classification


The NEC offers a system with letters that provide the ability to quickly identify wires. Some common wire lettering includes THHN, XHHW, THW, TFNN, etc.

Thermoplastic Flexible Fixture Nylon (TFFN) wire is best suited for fixtures, appliances, control circuits and machine tool wiring (MTW). This is because it is a stranded conductor, making it highly flexible and easy to connect to other surfaces.TFFN wire can withstand temperatures of up to 90 degrees C in dry conditions and up to 60 degrees C in wet conditions. It is also oil resistant. This makes it suitable for both indoor and outdoor environments.

Thermoplastic high heat resistant nylon (THHN) wire is best suited to carry high load currents of up to 600 volts in commercial and industrial environments. Its high heat resistance makes it an excellent conductor as it can withstand temperatures of up to 90 degrees Celsius for extended periods. However, this type of wire is fragile as it has only one protective layer. You should place the THHN wire into the conduit before burying to prevent damage.

Thermoplastic heat and water resistant nylon (THWN) wire is also suitable for commercial and industrial environments. It can conduct voltages up to 600 volts, although it is not uncommon to find types that conduct voltages as low as 110 volts. It is extremely durable, water and oil resistant and THWN wire can be run in wet environments for long periods without loss of performance. THWN wire is one of the best choices for electricians because of its durability and versatility for both indoor and outdoor environments.


Here are the letters and attributes you will often see in residential wiring.

  • T: Thermoplastic insulation
  • FF: Flexible clamps
  • H: Heat resistant
  • HH: High heat resistance (up to 194 degrees Celsius)
  • W: suitable for wet locations
  • N: Nylon coated, resistant to oil or gas damage
  • X: Synthetic polymer, flame resistant



Both THHN and THWN wire types are suitable for use in industrial environments. They are waterproof, conduct voltages of up to 600 volts and can withstand temperatures of up to 90 degrees Celsius. The key difference, however, is their durability. THWN wire is much better at resisting moisture and does not deteriorate in performance if exposed to water for long periods. THHN wire is better at resisting high temperatures for long periods, but it is not suitable for maximising performance in humid climates. It is also thinner and more fragile, which means you should place it in the conduit before use. Consider using THHN wire when you need optimum performance in dry climates and have heavy electrical loads that generate a lot of heat.


Wire colour


The colour of the wire is important as an industry standard for identifying the purpose of the wire. This is helpful for the next electrician on site and the advanced DIYer who plans to do some electrical work of their own. Don't let the colour of the wire make you think the wire is not hot. All electrical cords can carry loads and may be connected differently than the industry standard.

  • Black: hot wire for switches or sockets
  • Red: hot wire for switch legs and connection to hard-wired smoke detectors
  • Blue and yellow: hot wire through conduit; blue is commonly used for 3-way or 4-way switching applications and yellow for switch legs controlling fans, lights, etc.
  • White: neutral (may be hot if marked with black or red to indicate it is no longer neutral)
  • Green and bare copper: for grounding purposes only


Colour coded jackets for NM-B


Another industry standard that has been accepted over the years is colour coded jackets for non-metallic or NM-B wire (often also referred to as Romex, building wire or NM). Similar to the way specific wires are colour coded, colour coded jackets make it easy to identify the gauge of the wire inside.

  • White: 14 gauge wire, mainly used for lighting circuits
  • Yellow: 12 gauge wire, often used in the home to provide general power to sockets and most appliances
  • Orange: 10 gauge wire, typically used for air conditioning and water heaters
  • Black: 8 gauge and below, used to supply power to sub-panels, stoves, ovens etc.


Cable types


Armored Clad (AC) Cable: AC cable consisting of THHN insulated conductors with 16 gauge aluminium bonding wire placed inside the armour and used as a grounding conductor.

Automotive cable: This is a general purpose thermoplastic (GPT) wire, also known as a primary wire. Normal applications are in motor vehicles with limited exposure to liquids, physical wear and abuse.

Bayonet Neill-Concelman (BNC) cable: BNC cables are small quick connect/disconnect RF connectors for coaxial cables.

Category cables: Used in telephone systems and data network systems. cat 5e is the most common type of cable used for computer networks in internet service installations. Conductor pairs are twisted together to prevent crosstalk and interference from other pairs of conductors in the cable, as well as external interference. The higher the megahertz (MHz) capability, the more twist per foot.

Coaxial cable: This is a metal cable that carries television and video signals. It connects to video equipment and has a central conductor with a dielectric insulator, metal shield and plastic sheath.

Doorbell cable: Doorbell cable is used to connect wired doorbells or video doorbells to the home electrical system.18 Gauge cable is the most commonly used variety.

Double armoured cable: This is a durable cable that protects without the use of wire conduit, elbows, offsets (which can be expensive) or conduit connectors. For areas where the cable may be exposed to wet environments, the metal armouring protects against corrosion. 

Cord: Typically used for industrial machinery, washing machines and large appliances, portable tools, equipment and extension cords or power cords, cord/power cords have their naming convention based on letter codes, a common option is SJEOOW.

  • S: Service cord (when not followed by J, V or P; also indicates a voltage rating of 600 volts)
  • J: Primary service line, 300 volts
  • T: thermoplastic
  • E: Elastomer, thermoplastic with the look and feel of rubber
  • O: oil-resistant outer sheath
  • OO: oil-resistant outer sheath and oil-resistant insulation
  • P: Parallel wire (light, flat)
  • V: Vacuum cleaner cord (light, round)
  • W: sunlight and moisture resistant

Lamp cord: for lamps, small appliances, radios and other similar products up to 300 volts, lamp cord is available in sizes 18 to 12 and a wide range of colours. 

Landscape Lighting Low Voltage (LV) Cable: This underground cable is suitable for outdoor accent lighting, landscape lighting and security lighting. Applications should not exceed 150 volts. It is intended for direct burial and is suitable for sunlight exposure and is available in sizes 16 and 8.

Metal Clad (MC) cable: MC cable is used extensively in commercial electrical work, for running through concrete or other commercial environments. A separate THHN conductor is run through the aluminium interlocking armour. It includes an earth wire.

Mobile Home Feeder: Connects mobile homes to electrical supplies where permanent wiring is required, suitable for direct burial and underground service entrance cables. It consists of four RHH or RHW-2 conductors, with a white stripe for the neutral and a green earth conductor. It is sunlight resistant.

Network and data cable: This comes in three types - fibre optic, twisted pair and coaxial cable - for connecting multiple network devices or computers in a network.

NM-B: This is a non-metallic sheathed cable used as residential building wire for branch circuits for outlets, lighting and other residential applications. NM-B is available between 14 AWG and 6 AWG with two or three conductors.

Pre-assembled Whips: These are pre-cut lengths of armoured cable designed to increase jobsite productivity. Assemblies come with pre-stripped THHN conductors and pre-installed zinc die-cast, snap-in fittings.

Residential Earthing Wire: This is a bare copper wire available in 4, 6 and 8 gauge solid and stranded construction. It is used to ground the residential electrical system, usually at the meter before entering the home. It is also used to ground the perimeter surface around the pool.

Service Entry Cable: This consists of a single conductor rated XHHW-2 or THHN/THWN and supplies power from the main breaker to the sub-panel. It can be exposed to direct sunlight or used in wet or dry locations.

  • SE-R: SE-R is twisted with bare ground and is used to bring service from the panel to other panels in multi-unit dwellings and SE-U applications.
  • SE-U: Bare conductor stranded wire spirally wound on two parallel insulated conductors. It is used in single-family dwellings to carry electricity from the service splitter to the meter base and from the meter base to the distribution panel.

Speaker wire: Made of copper and designed to carry low voltage currents, speaker wire has a variety of wiring uses including doorbells, thermostats, home security sensors, landscape lighting and other low current systems. 

Sprinkler wire: Multi-conductor sprinkler wire is suitable for direct burial in applications up to 30 volts. It is used in central control systems for underground sprinkler systems and is available in 18 gauge construction with up to 25 conductors.

Submersible pump cable: This consists of THWN copper conductors that are heat-, moisture-, oil- and petrol-resistant. It is suitable for use with two or three conductors at temperatures below 75 degrees Celsius. It is used for the power supply and circuit of submersible pump systems.

Thermostat wire: Used in heating and air conditioning systems, as well as bell and alarm systems, thermostat wire is available in 20 or 18 gauge sizes with up to 10 conductors.

Underground (UF-B) wire: copper wire for underground use, including direct burial, which is grey sheathed and can be used for deck lighting, outdoor water features, landscape lighting and air conditioning compressors.

Underground Residential Distribution (URD) cable: for secondary distribution and underground service applications of 600 volts or less, suitable for direct burial or placement in conduit. It is acceptable in wet locations on the third or fourth floor. Conductors are stranded compressed aluminium. The neutral conductor has a yellow triple extruded stripe.


Tools and accessories


Use wire strippers to remove the sheathing from the cable.

When completing electrical projects, it is important to have the correct tools and safety equipment to get the job done. Check out some of the most commonly used tools in an electrician's toolbox.


  1. Boxes and Covers: These are used to hold sockets and adapters for operating lights, ceiling fans, kitchen appliances, etc.
  2. Circuit breakers and fuses: These are two types of devices used to prevent damage to electrical currents caused by overloads or short circuits. Circuit breakers and fuses interrupt the current during an overload or short circuit and are installed in a circuit breaker box or fuse box. houses built after the 1960s usually use circuit breakers rather than fuses.
  3. Electrical tape: Used to repair or insulate electrical wiring, electrical tape is usually black. It can be used to identify wires and should be stretched for better adhesion when applied.
  4. Electrical tester: Checking a circuit to make sure it is not electrically charged can be a life-saving decision. An electrical tester will quickly inform you if a live cable is being used.
  5. Sockets and adapters: When a cord is connected to a socket or adapter, it allows current to power whatever is plugged into it, such as kitchen appliances.
  6. Plugs and connectors: These are usually connected by a device or power cord and plugged into a wall socket. They allow the device to receive power from the socket.
  7. Wire connectors: these connect two wires with a connector: the bare end of each wire is inserted into the connector and twisted for connection. Watch our DIY basics video: How do you connect two wires?
  8. Wire/Cable cutter: this tool is used to cut wires and cables directly. There are various cutters for different jobs, so check that you are using the right one, whether you are cutting copper or network cables.
  9. Wire stripper: This device removes the plastic casing to expose the bare wire underneath. Most wire strippers offer multiple slots for various wire sizes, while some have an adjustment dial to set the correct size. Simply insert the wire into the correct size slot, twist and pull out.


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