MECKLENBURG COUNTY Land Use and Environmental Service Agency Code Enforcement 2/8/12 ELECTRICAL CONSISTENCY MEETING Code Consistency Questions 1. I am inspecting a building addition. They have a 480V to 120/208V 150 KVA step down transformer with two 225 amp panels being fed from it, but now have more circuits than these two panelboards can handle. Can they tap an additional 100 amp panel off of this transformer? The 100 ampere panel would be 15 feet away. If the primary side is protected at 125% of the transformer rating and the secondary panel satisfy grouping and tap rules, then this installation is code compliant If the primary side is protected at greater than 125%, then this installation does not comply with the NEC. 2. What is the maximum length of raceway I can use where the conductor ampacity is not required to be adjusted for conductor bundling? See Note 4 to Table 1 of Chapter 9 that states Where conduit or tubing nipples having a maximum length not to exceed 600 mm (24 in.) are installed between boxes, cabinets, and similar enclosures, the nipples shall be permitted to be filled to 60 percent of their total cross-sectional area, and 310.15(B)(2)(a) adjustment factors need not apply to this condition. See also 310.15(B)(2(a) Exception No. 3 that states Derating factors shall not apply to conductors in nipples having a length not exceeding 600 mm (24 in.). 3. We have a 400A, 3-phase feeder that we want to wire with two parallel sets of 3/0 AWG conductors in the same raceway. Is this acceptable?
Page 2 of 6 Yes, see 310.4 (A) and (C) as there is nothing wrong with this installation. However, derating will be required. See 310.15(B)(2) Adjustment Factors, (a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of currentcarrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). 4. Our utility requires a non-fused disconnect upstream of the meter and service disconnect for certain services. Is this legal? If this is the first disconnect, do we separate the grounded and grounding conductors at this point? See 230.82 (3) that states Meter disconnect switches nominally rated not in excess of 600 volts that have a short-circuit current rating equal to or greater than the available short-circuit current, provided all metal housings and service enclosures are grounded in accordance with Part VII and bonded in accordance with Part V of Article 250. A meter disconnect switch shall be capable of interrupting the load served. These are used because self-contained meters and internal meter bypass switches may not be able to safely disconnect 277/480 volt services under load. This is not the service disconnecting means, so for Article 250 purposes, pretend that this switch does not exist. 5. If structural steel is used as a grounding electrode for the electrical service, is it also necessary to supplement the steel electrode with an additional electrode such as a ground rod? If structural steel is high and dry can it be converted to a grounding electrode? Specific answer - No, once structural steel in established as an electrode, it does not have to be further supplemented by an additional electrode. Also an answer - No, if (10 ft) or more of a single structural metal member is in direct contact with the earth or encased in concrete that is in direct contact with the earth. For the 2008 NEC, connecting the metal frame of the building to an additional electrode such as a ground rod would make the metal frame of the building an
Page 3 of 6 electrode. This has been revised for the 2011 NEC. The Article 100 definition of a grounding electrode is a conducting object through which a direct connection to earth is established. For correct application of this definition, the structure metal members of a building or structure needs to be the conducting object with a direct connection to the earth. 250.52 Grounding Electrodes. (2008 NEC) (A) Electrodes Permitted for Grounding. (2) Metal Frame of the Building or Structure. The metal frame of the building or structure that is connected to the earth by any of the following methods: (1) 3.0 m (10 ft) or more of a single structural metal member in direct contact with the earth or encased in concrete that is in direct contact with the earth (2) Connecting the structural metal frame to the reinforcing bars of a concreteencased electrode as provided in 250.52(A)(3) or ground ring as provided in 250.52(A)(4) (3) Bonding the structural metal frame to one or more of the grounding electrodes as defined in 250.52(A)(5) or (A)(7) that comply with 250.56 (4) Other approved means of establishing a connection to earth 250.52 Grounding Electrodes. (2011 NEC) (A) Electrodes Permitted for Grounding (2) Metal Frame of the Building or Structure. The metal frame of the building or structure that is connected to the earth by one or more of the following methods: (1) At least one structural metal member that is in direct contact with the earth for 3.0 m (10 ft) or more, with or without concrete encasement. (2) The hold-down bolts securing the structural steel column are connected to a concrete encased electrode that complies with 250.52(A)(3) located in the support footing or foundation. The hold-down bolts shall be connected to the concreteencased electrode by welding, exothermic welding, the usual steel tie wires, or other approved means. 6. When a conduit leaves a Class I, Division 1 classified paint spray room and goes under the concrete floor into a cabinet in the motor control room that is non-classified, is one sealing fitting in the paint mix room sufficient, or is an additional sealing fitting required in the nonclassified area as well? 516.4 sends us to Article 501 or 505 for wiring methods. 501.15(A)(4) contains the sealing rules. If it can be located to minimize the communication of fumes in the
Page 4 of 6 conduit one will suffice. 7. A service equipment panel-board has a 400 amp main which feeds a bus that has double barrel lugs at the bottom, and then feeds two 200 ampere disconnects. Is it permissible to tap directly from the double barrel lugs of a service equipment panel-board? Yes, see 240.21 and 110.14(C). The tap rules are covered in 240.21 and the termination requirements in 110.14(C). As long as the conductors are being terminated in accordance with the permitted markings for the lugs and the appropriate tap rule is being followed with a 400A breaker protecting the feeder, there is no violation to supply tap conductors from a sub-feed lug on the panelboard. It would appear that either the 10ft or 25 ft tap would be permitted in this installation. 8. We have motors that are interlocked, preventing them from being on at the same time. Do we still have to add them all up for service and feeder calculations? No. See 430.24, Exception No. 3 that states Where the circuitry is interlocked so as to prevent operation of selected motors or other loads at the same time, the conductor ampacity shall be permitted to be based on the summation of the currents of the motors and other loads to be operated at the same time that results in the highest total current. For service ampacity, 230.42 Minimum Size and Rating (A) General, references Part III of Article 220. Section 220.50 Motors refers to 430.24 as shown above. Also see 220.60 that states Where it is unlikely that two or more noncoincident loads will be in use simultaneously, it shall be permissible to use only the largest load(s) that will be used at one time for calculating the total load of a feeder or service. 9. I was doing a swimming pool job that included a motor, wet niche fixture, and metal forming shell. When installing the equipotential bonding grid, I split bolted a #8 copper jumper from the forming shell to the light niche and one from the forming shell to the motor. The inspector turned me down saying the grid could not be a component in bonding the niche to the other metal parts. Is she correct? 680.26 Equipotential Bonding.
Page 5 of 6 (A) Performance. The equipotential bonding required by this section shall be installed to reduce voltage gradients in the pool area. (B) Bonded Parts. The parts specified in 680.26(B)(1) through (B)(7) shall be bonded together using solid copper conductors, insulated covered, or bare, not smaller than 8 AWG or with rigid metal conduit of brass or other identified corrosion-resistant metal. Connections to bonded parts shall be made in accordance with 250.8. An 8 AWG or larger solid copper bonding conductor provided to reduce voltage gradients in the pool area shall not be required to be extended or attached to remote panelboards, service equipment, or electrodes. 10. I understand the Code allows me to use Type AC cable with an equipment grounding (bonding) conductor for branch circuits serving patient care areas. Can I use Type MC Cable with an equipment grounding (bonding) conductor for luminaires located above 7.5 feet in a patient care area? Yes, see 517.13, Grounding of Receptacles and Fixed Electrical Equipment in Patient Care Areas, that states Wiring in patient care areas shall comply with 517.13(A) and (B). Section (A) Wiring Methods states All branch circuits serving patient care areas shall be provided with an effective ground-fault current path by installation in a metal raceway system, or a cable having a metallic armor or sheath assembly. The metal raceway system, or metallic cable armor, or sheath assembly shall itself qualify as an equipment grounding conductor in accordance with 250.118. 11. What is the maximum number of bathroom receptacles that can be placed on the 20A, 120V bathroom receptacle circuit in a single-family dwelling? Could you elaborate on other options for bathroom receptacles requirements. Question 1 There is no maximum. See 210.11(C)(3) that states In addition to the number of branch circuits required by other parts of this section, at least one 20-ampere branch circuit shall be provided to supply bathroom receptacle outlet(s). Such circuits shall have no other outlets. The see 220.14(J) and (J)(1) that states one-family, two-family, and multifamily dwellings the outlets specified in (J)(1), (J)(2), and (J)(3) are included in the general lighting load calculations of 220.12. No additional load calculations shall be required for such outlets. 220.14(J)(1) states All general-use receptacle outlets of 20-ampere rating or less, including receptacles connected to the circuits in 210.11(C)(3).
Page 6 of 6 12. What sections of the NEC would apply to piers and docks at single family dwellings? Would Article 682 apply? All of the normal sections that apply to single family dwellings would apply to piers and docks at single family dwellings. Article 682 could apply since it is not specifically excluded. 210.8 Ground-Fault Circuit-Interrupter Protection for Personnel. FPN: See 215.9 for ground-fault circuit-interrupter protection for personnel on feeders. (A) Dwelling Units. All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in (1) through (8) shall have ground-fault circuit-interrupter protection for personnel. (3) Outdoors (C) Boat Hoists. GFCI protection shall be provided for outlets not exceeding 240 volts that supply boat hoists installed in dwelling unit locations.