Wire lettering. Types of wires

Wire lettering

The letters THHN, THWN, THW and XHHN represent the main in- sulation types of individual wires. These letters depict the following NEC (National Electric Code) requirements:

· T – Thermoplastic insulation

· H – Heat resistance

· HH – High heat resistance (up to 194°F)

· W – Suitable for wet locations

· N – Nylon coating, resistant to damage by oil or gas

· X – Synthetic polymer that is flame-resistant

Types of wires

There are mainly 5 types of wire:

·

Triplex wires: Triplex wires are usually used in single-phase service drop conductors, between the power pole and weatherheads. They are composed of two insulated aluminum wires wrapped with a third bare wire which is used as a common neutral. The neutral is usually of a smaller

gauge and grounded at both the electric meter and the transformer.

· Main feeder wires: Main power feeder wires are the wires that connect the service weatherhead to the house. They’re made with stranded or solid THHN wire and the cable installed is 25% more than the load required.

· Panel feed wires: Panel feed cables are gener-

ally black insulated THHN wire. These are used to power the main junc-

tion box and the circuit breaker panels. Just like main power feeder wires, the cables should be rated for 25% more than the actual load.

·

Non-metallic sheathed wires: Non-metallic sheath wire, or Romex, is used in most homes and has 2-3 conductors, each with plastic insula- tion, and a bare ground wire. The in- dividual wires are covered with an- other layer of non-metallic sheathing. Since it’s relatively cheaper and avail- able in ratings for 15, 20 and 20 amps, this type is preferred for in-house wir- ing.

· Single strand wires: Single strand wire also uses THHN wire, though there are other variants. Each wire is separate and multiple wires can be drawn together through a pipe easily. Single strand wires are the most popular choice for layouts that use pipes to contain wires.