When you’re choosing the wires and cables that will bring electricity into your home, there are a few factors that you should consider.
All cables and wires will have labels on them indicating what they are best used for. Never buy a cable or wire that does not have this labelling, as they may turn out to be unsafe for your purposes.
Wires will always have THHN or THWN printed on their coverings. These letter combinations indicate the following information: T stands for thermoplastic insulation, H stands for heat resistance, a second H stands for high heat resistance, W stands for wet conditions resistance, and N means that the wire won’t be damaged by oil or gas.
You will find that most wires say CU on the sheath as well – this means that the wires are made from copper, which the most common conductor used in residential electrical work.
The maximum voltage will also be listed, usually in the 600 region. This is the largest amount of electricity the wires can conduct. The gauge is the size of the wire, usually 10, 12 or 14.
The most common type of cable used for indoor residential electrical work is an NM-B cable. These are ‘non-metallic’ cables – the sheathing is usually made from a flexible PVC material rather than some metal.
The B stands for the cable’s heat rating. A B rating means the cable can handle up to 194 degrees Fahrenheit before it starts to overheat. It’s very rare that a B cable would ever overheat to this point, which is why it’s the preferred residential choice – you want to avoid, at all costs, melting the insulation, which can lead to fire and serious safety hazards.
There are also armored cables, UF cables, metal-clad cables, coaxial cables and category 5-E cables, but as mentioned in Part 1 of this series, it’s best to leave the electrical work to the experts. Make sure you hire an electrician with a proven track record, then have him let you know which cables need to be purchased, or if he will organise them himself.