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Service Maintenance Company, Inc. Electrical Contractors |
| NEC Questions | 11/14/2003 |
| By Mike Holt, for EC&M Magazine Q1. I can't recall anything in the NEC about the orientation of a panel. Is there a specific way that it has to be mounted? I have come across some customers who prefer that the panel be mounted horizontally instead of vertically? A1. 240.33 Vertical Position Enclosures containing overcurrent protection devices shall be mounted in a vertical position unless this is impracticable. Circuit breaker enclosures can be installed horizontally, if the circuit breakers are installed in accordance with 240.81. Figure 240-28 Section 240.81 specifies that where circuit breaker handles are operated vertically, the "up" position of the handle shall be in the "on" position. So in effect, an enclosure that contains one circuit breaker can be mounted horizontally, but an enclosure containing a panelboard with multiple circuit breakers would have to be mounted vertically. Q2. Is GFCI protection required for a 20A, single-phase 208V pool pump motor that is hard wired? A2. No, but the1999 NEC text in 680.22(A)(1) gave the impression that GFCI protection was required for hard-wired pool pump motors. Q3. How is the working space width requirement of 110.26(A)(2) measured? A4. The working space shall be a minimum of 30 in. wide, but in no case less than the width of the equipment. The width of the working space is measured from left to right, from right to left, or simply from the centerline of the equipment. In all cases, the working space shall be of sufficient width, depth, and height to permit at least a 90° opening of all equipment doors. Q3. What is the maximum grounding electrode resistance required by the NEC? I have heard values ranging from 25 ohms to as little as 1 ohm. A3. There is no maximum grounding electrode resistance; however, when the resistance of a single ground rod is over 25 ohms, one additional electrode shall be installed at least 6 ft away to augment the single ground rod electrode [250.56]. The NEC does not require more than two ground rods to be installed, even if the total resistance of the two parallel ground rods exceeds 25 ohms. The grounding electrode conductor to the first ground rod, and between the two ground rods is not required to be larger than 6 AWG [250.66(A)]. Q4. Can a 24V Class 2 cable containing conductors for control or signaling be run in the same raceway with 120V power conductors? A4. The general requirement is that Class 2 circuit conductors shall not be placed in the same raceway with conductors of power or Class 1 conductors [725.55(A)(1)]. However, a Class 2 circuit can be installed with power or Class 1 circuits, if the Class 2 circuit is reclassified as Class 1 and installed in accordance with the requirements for Class 1 Circuit (Article 725, Part II). In addition, the Class 2 marking on the equipment must be removed, and overcurrent protection is provided in accordance with 725.23 [725.52(A)(1) Ex No. 2]. One final comment, Class 1 circuits are only permitted to be in the same cable, enclosure or raceway with power-supply circuits where the equipment powered is functionally associated with the Class 1 circuit [725.26(B)(1)]. Q5. I have wired many pools over the years and I always used Type UF cable underground for the pool pump motor. A new inspector is telling me that the NEC does not permit this. What the deal? A5. Type UF is not permitted outdoors for pool, spa or hot tub wiring [680.21(A)], except as a supply for a double insulated motor [680.21(B)]. Q6. Can communications cable be installed within supply and return air ducts? A6. Yes. Communications cables can be installed in ducts, plenums, and other spaces used for environmental air, but the cable must be Type CMP [800.53(A)]. Q7. What is the reason we are required to ground separately derived systems to an acceptable electrode (earth)? A7. I don't think there is any technical reason to ground a separately derived system to an electrode. Because a separately derived system is required to be bonded to the metal parts of the electrical installation [250.30(A)(1)] this establishes a zero system reference, stabilizes the system, and provides the low impedance path necessary to clear a ground fault. Oh yeah, system bonding [250.30(A)(1)] automatically grounds the system to the building grounding electrode system, via the effective ground-fault path. Mike C, we need a graphic for this point. Q9. I learned today that the state electrical inspector does not require electrical equipment to be listed or labeled. As a result unlisted equipment is typically installed in our industrial facility. Does the inspector have the right to wave this significant NEC requirement? A9. The NEC does not require all electrical equipment to be listed, it specifies that the authority having jurisdiction (AHJ) has the responsibility for deciding on the approval of equipment and materials [90.4 and 110.2]. The key to understanding this concept is that electrical equipment is required to be "approved" by the AHJ, not "listed or labeled." Approved, means "acceptable to the authority having jurisdiction" [Article 100]. However, listing and labeling is often the basis for approval [90.7], and Section 110.3 provides guidance for the evaluation of equipment by the AHJ. Q10. I am going to run three rigid nonmetallic conduits, each containing 500 kcmil conductors, to supply a 1200A panel. According to Table 250.122, I am required to supply a 3/0 AWG ground wire. Do I have to pull a ground wire in each of the conduits? A10. Well let's first get the feeder conductor properly sized. A 1200A feeder requires 600 kcmil conductors, not 500 kcmil. This is because the ampacity of 500 kcmil is only rated 1140A (380A x 3) at 75C [110.14(C) and 240.4(C)]. Now to your question. The equipment grounding (bonding) conductor is required to be a minimum of 3/0 AWG, and it is required to be installed in each of the raceways. Q11. What is the minimum wire size permitted for an extension cord that is plugged in a 20A circuit? A11. Section 240.5(B)(3) permits listed extension cord sets of 16 AWG or larger to be protected by 20A or less branch-circuit overcurrent devices. Q12. In our industrial facility, we use cords for motor connections in a Class I hazardous location. I have been told that the cord is required to be explosionproof. Is there such a thing as an explosionproof cord? A12. There is no such thing as an explosionproof cord. This is because the NEC only requires that the cord be of a type listed for extra-hard usage in accordance with Table 400.4. View html version here: Copyright © 2003 Mike Holt Enterprises,Inc. |
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