How do you know the proper identification, construction application, and ampacity for phase conductors? Follow this article for NEC guidelines.
An ungrounded conductor is a circuit conductor that carries current to the load. We usually call ungrounded conductors in a service, feeder, or branch-circuit phase conductors. When working with these, you must be familiar with the National Electrical Code (NEC) regarding proper identification, construction, application, and ampacity.
Conductor identification. Properly identifying conductors in electrical wiring systems protects you and others. It's essential for you to recognize (by color or other means of identification) the ungrounded phase conductor, grounded neutral conductor, and equipment-grounding conductor (EGC) in an electrical circuit. You must also connect these same conductors to color-coded or marked terminals of electrical equipment.
Prior to 1975, the Code recommended a color-code scheme for ungrounded phase conductors. Subsequent editions of the Code only require color coding for a grounded phase conductor or neutral conductor and the EGC. However, you must designate the high-leg of a delta system with orange, or mark it properly for easy identification.
Where more than one nominal voltage system exists in a building's wiring system, Sec. 210-4(d) requires you to identify the ungrounded phase conductors of multiwire circuits. You can mark the conductors with tape, tag them, use spray paint (where permitted), or other effective means accepted by the authority having jurisdiction (AHJ) to properly identify them. You must also identify the conductor by phase and system voltage. Note: This is not a color-code requirement, it's a means of identification so you can easily determine and identify each system's voltage.
The Code requires you to permanently post the means of identification at each branch-circuit panelboard. However, the requirement to color-code or identify these circuits does not apply unless you run them in the same raceway junction box, etc.
Conductor construction and application. The Code requires you to insulate ungrounded phase conductors used for general wiring; however, it doesn't require the use of insulation in some types of installations. The insulation must be approved for the voltage, operating temperature, and location of use.
Table 310-13 of the NEC lists the different types of insulated conductors used for general wiring. You may use the conductors listed for any voltage up to and including 600V.
Some conductor types are suitable for dry, damp, or wet locations only. Still others are suitable for combinations of such. You may not use conductors listed as suitable for dry locations in wet places. You can use the conductors listed in Table 310-13 in any of the wiring methods recognized in Chapter 3.
Insulation resistance can vary a great deal when exposed to different temperatures. The resistance is higher at lower temperatures and steadily decreases as the temperature rises. So if you measure the insulation resistance of a conductor exposed to high temperatures, you'll get a much lower reading than if you test it while the conductor is cool.
Thermoplastic insulation may stiffen at temperatures colder than 110DegrC (+14DegrF). This is important to remember if you're installing this type of conductor on a cold winter day. Keep in mind, thermoplastic insulation may also deform at points of support; even in normal temperatures.
The NEC also gives rules for the installation of conductors in wet locations. What exactly is a wet location? A wet location is where condensation or accumulation of moisture within the raceway is likely to occur, and where you place a conductor underground, in concrete slabs or masonry that is in direct contact with the earth (or subject to moisture).
If placing a cable in one of these locations, you must select one designated for use in wet locations, or you could install a cable equipped with a lead sheath.
The NEC considers the following types of insulation to be moisture-resistant: RHW and RWH-2; MTH; THHW; TW; THW and THW-2; THWN, THWN-2; Z and ZW; XHHW; lead covered or other; and other types specifically listed for use in wet locations.
Ampacity of conductors. Table 310-16 lists the allowable ampacities of insulated conductors rated 0V to 2000V with a temperature rating of 60DegrC through 90DegrC (140DegrF through 194DegrF). This table also states you shall have no more than three current-carrying insulated conductors enclosed in a raceway, cable, or buried side by side in the earth. The ratings are based on an ambient temperature of 30DegrC (86DegrF).
If the ambient temperature is above 86DegrF, you must adjust the ampacity of the conductor by applying a correction factor. In general, if the ambient temperature is below 86DegrF, you'll gain ampacity. If the ambient temperature is above 86DegrF, conductor ampacity decreases.
If you are going to install more than three current-carrying conductors in a raceway or cable, you must adjust (decrease) the ampacity of each conductor. The correction factors are shown in Table 310-15(b)(2)(a).