|
Q1. What conductor types does the NEC permit to be used in dry and damp locations?
A1. Insulated conductors typically used in dry and damp locations include Types THHN, THHW, THWN, or THWN 2. Other conductor insulations that can be used are Types FEB, FEPB, MTH, PFA, RHH, RHW, RHW-2, and SA. [310.10(B)].
Author's Comment:
• Refer to Table 310.104 for a complete list of conductors that may be installed in dry or damp locations. See Table 400.4 for the use of flexible cords and flexible cable permitted in dry or damp locations.
Q2. What conductor types does the NEC permit to be used in wet locations?
A2. Insulated conductors typically used in wet locations include:
Types THHW, THWN, THWN 2, XHHW, or XHHW 2. Other conductor insulations used in wet locations are MTW, RHW, RHW-2 and SA [310.10(C)].
Author's Comment:
• Refer to Table 310.104 for a complete list of conductors that may be installed in wet locations. See Table 400.4 for the use of flexible cords and flexible cable permitted in wet locations.
• The letter W found on the insulation types listed here indicate that installation is suitable for wet locations.
Q3. What does the NEC require of conductors in order to use them in locations exposed to direct sunlight?
A3. Insulated conductors and cables exposed to the direct rays of the sun must be [310.10(D)]:
(1) Listed as sunlight resistant or marked as being sunlight resistant.
Author's Comment:
• SE cable and the conductors contained in the cable are listed as sunlight resistant. However, according to the UL listing standard, the conductors contained in SE cable aren't required to be marked as sunlight resistant.
• Types TW, THW, THW-2, THHW, THWN, and THWN-2 are some of the insulation types the may me marked Sunlight Resistant UL White Book].
(2) Covered with insulating material, such as tape or sleeving materials that are listed as being sunlight resistant or marked as being sunlight resistant.
Q4. What does the NEC require of conductors in order to use them in corrosive locations?
A4. Conductor insulation must be suitable for any substance to which it may be exposed that may have a detrimental effect on the conductor's insulation, such as oil, grease, vapor, gases, fumes, liquids, or other substances. See 110.11. [310.10(G)]
Q5. What is the Code requirement in regard to installing single conductors outside of a raceway or cable?
A5. Single conductors must be installed within a Chapter 3 wiring method, such as a raceway, cable, or enclosure [300.3(A)]. They can also be installed in a cable tray when 1/0 AWG or larger [392.20(A)].
Overhead conductors can be installed in accordance with 225.6 [300.3(A) Ex].
Q6. What is the NEC requirement on grouping circuit conductors together?
A6. Conductors of the same circuit and, where used, the neutral and equipment grounding and bonding conductors must be installed in the same raceway, cable, trench, cord, or cable tray, except as permitted by 300.3(B)(1) through (4).
(1) Paralleled Installations. Conductors installed in parallel in accordance with 310.10(H) must have all circuit conductors within the same raceway, cable tray, trench, or cable.
Author's Comment:
• To minimize induction heating of ferrous metal raceways and ferrous metal enclosures for alternating-current circuits, and to maintain an effective ground-fault current path, all conductors of a circuit must be installed in the same raceway, cable, trench, cord, or cable tray. See 250.102(E), 300.3(B), 300.5(I), 300.20(A), and 392.8(D).
Exception Parallel phase and neutral conductors can be installed in individual underground nonmetallic raceways (Phase A in raceway 1, Phase B in raceway 2, and so forth) as permitted by 300.5(I) Ex 2, if the installation complies with 300.20(B).
(2) Outside a Raceway or an Enclosure. Equipment grounding jumpers can be located outside of a flexible raceway if the bonding jumper is installed in accordance with 250.102(E)(2).
For dc circuits, the equipment grounding conductor can be run separately from the circuit conductors in accordance with 250.134(B) Ex 2.
(3) Nonferrous Wiring Methods. Circuit conductors can be installed in different raceways (Phase A in raceway 1, Phase B in raceway 2, and so on) if, in order to reduce or eliminate inductive heating, the raceway is nonmetallic or nonmagnetic and the installation complies with 300.20(B). See 300.3(B)(1) and 300.5(I) Ex 2.
(C) Conductors of Different Systems.
(1) Mixing. Power conductors of alternating current and direct
current systems rated 1,000V or less can occupy the same raceway, cable, or enclosure if all conductors have an insulation voltage rating not less than the maximum circuit voltage. Figure 01 Š
Informational Note 1: See 725.136(A) for Class 2 and Class 3 circuit conductors.
Author's Comment:
- Control, signal, and communications wiring must be separated from power and lighting circuits so the higher voltage conductors don't accidentally energize the control, signal, or communications wiring:
▫ Class 1 control circuits, 725.48
▫ Class 2 and Class 3 Control Circuits, 725.136(A)
▫ Communications Circuits, 800.133(A)(1)(c)
▫ Coaxial Cable, 820.133(A)
▫ Fire Alarm Circuits, 760.136(A)
▫ Sound Circuits, 640.9(C)
- Class 1 circuit conductors can be installed with associated power conductors [725.48(B)(1)] if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].
- A Class 2 circuit that's been reclassified as a Class 1 circuit [725.130(A) Ex 2] can be installed with associated power conductors [725.48(B)(1)] if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].
|
