Have You Been Grounded Lately

Transcription

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2 Have You Been Grounded Lately Thurs, Oct. 26, :15-10:15 Phil Simmons Author, Electrical Grounding and Bonding

3 Author Cengage Learning Phil Simmons

4 Have You Been Grounded Lately 2017 NEC Changes Relative to Grounding and Bonding

5 250.24(C)(1) Sizing for Single Raceway or Cable (1 of 4) Grounded system conductor (often a neutral) is required to be not smaller than the conductor specified in Table (C)(1) Not required to be larger than the largest ungrounded service-entrance conductor Rule contemplates all service conductors are in a single conduit, wireway or cable

6 250.24(C)(1) Sizing for Single Raceway or Cable (2 of 4) Here s how: Obtain size of service-entrance conductors Use the size of these conductors in Table (C)(1) to determine the minimum size of the grounded system conductor Compare to the size of grounded conductor required from load calculation in Follow instructions from design engineer Install the largest of these conductors

7 250.24(C)(1) Sizing for Single Raceway or Cable (3 of 4) For parallel sets of conductors installed in compliance with (H): If in one raceway such as a wireway or cable, determine the area of the largest set of conductors in parallel and consider as one conductor Follow Table (C)(1) for the minimum size of neutral conductor If the area of an ungrounded set of conductors is larger than Table (C)(1), apply the 12.5% rule

8 250.24(C)(1) Sizing for Single Raceway or Cable (4 of 4) FIGURE 2-28 Routing and sizing of grounded conductor for individual service disconnects, (C)(1).

9 Here s How (Grounded Service Conductor) (1 of 3) 350 kcmil aluminum service lateral conductors in each conduit or cable Table (C)(1) = 2 AWG copper or 1/0 aluminum Compare to size required by load calculation Minimum 1/0 AWG for parallel installations Install largest required conductor

10 Here s How (Grounded Service Conductor) (2 of 3) 3/0 AWG copper conductors to 200 ampere service disconnect Table (C)(1) requires 4 AWG copper or 2 AWG aluminum grounded conductor Larger conductor may be required by load calculation

11 Here s How (Grounded Service Conductor) (3 of 3) 500 kcmil copper conductors to 400 ampere service disconnect Table (C)(1) requires 1/0 AWG copper or 3/0 AWG aluminum grounded conductor Larger conductor may be required if load calculation exceeds 380 amperes

12 250.30(A)(4) Grounding Electrode Grounding electrode system for building or structure required to be used for separately derived system Comply with (C) if the separately derived system is located outdoors FIGURE 2-52 Grounding electrodes for separately derived systems, (A)(4).

13 250.30(A)(4) Grounding Electrode Previously we were permitted to install an individual grounding electrode for a separately derived system. If that is done, the grounding electrodes at the same building or structure are required to be bonded together Building steel or qualified metal water pipe are permitted as the grounding electrode conductor.

14 250.30(A)(4) GEC, Single Separately Derived System Connect grounded conductor of separately derived system to grounding electrode or grounding electrode conductor Connect at same point where system bonding jumper is connected FIGURE 2-53 Grounding electrode conductor, single separately derived system, (A)(5).

15 Here s How (Single Separately Derived System) Assume 600-ampere panelboard Two 350 kcmil THWN conductors connected in parallel 310 amperes x 2 = 620 amperes 350 kcmil x 2 = 700 kcmil Table requires 2/0 AWG copper grounding electrode conductor

16 Common GEC Common grounding electrode and tap conductors permitted Connect taps at same point system bonding jumper is connected This subsection acts as an exception to (A)(5) FIGURE 2-55 Grounding electrode conductor (GEC), multiple separately derived systems, (A)(6).

17 250.52(A)(2) Metal In-Ground Support Structure Methods of making an earth connection of the metal frame of the building or structure are described Requires direct contact with the earth, concrete encasement or by connection to concrete encased grounding electrode Once a recognized grounding electrode, it can be used to bond other electrodes

18 Metal Inground Support Structure FIGURE 3-3 Metal in-ground support structure grounding electrode, (A)(2).

19 FIGURE 3-1 Grounding electrode system,

20 250.52(B) Electrodes Not Permitted for Grounding Metal underground gas piping systems [Interior piping systems required to be bonded by (B)] Aluminum electrodes The structures and structural reinforcing steel described in (B)(1) and (2) FIGURE 3-9 Electrodes not permitted for grounding, (B).

21 680.26(B)(1) and (B)(2) (B)(1) Conductive Pool Shells Structural Reinforcing Steel Copper Conductor Grid (B)(2) Perimeter Surfaces Structural Reinforcing Steel Alternate Means Not permitted as grounding electrode These conductive elements are almost always connected to the electrical system by the equipment grounding conductor

22 250.64(B) Securing and Protection Against Physical Damage (1 of 2) If exposed, grounding electrode conductor or enclosure must be securely fastened Permitted to be installed on or through framing members 1) 6 AWG or larger not exposed to physical damage is permitted to be run along the surface of a building without metal covering or protection 2) 6 AWG or larger conductor that is exposed to physical damage must be protected by RMC, IMC, PVC, RTRC-XW, EMT or cable armor

23 250.64(B) Securing and Protection Against Physical Damage (2 of 2) 3) Grounding electrode conductors smaller than 6 AWG must be protected by: Rigid metal conduit (RMC) Intermediate metal conduit (IMC) Rigid nonmetallic conduit (PVC) RTRC-XW EMT Cable armor 4) Not required to comply with the burial depths of but must be protected if subject to damage

24 250.64(E) Raceways and Enclosures for Grounding Electrode Conductors General Ferrous metal enclosures for grounding electrode conductors are required to be electrically continuous from point of attachment to cabinets or equipment to the grounding electrode to create a parallel path and must be securely fastened to the ground clamp or fitting (2) Methods Bonding must be in compliance with (B) and ensured by one of the methods in (B)(2) through (B)(4)

25 250.64(E) Bonding Requirements (3) Size The bonding jumper for a grounding electrode conductor raceway or cable armor is required to be the same size as, or larger than, the enclosed grounding electrode conductor FIGURE 3-38 Bonding of ferrous enclosures for grounding electrode conductors, (E).

26 250.64(E) Bonding Requirements (2 of 2) (4) Wiring Methods If a raceway is used as protection for a grounding electrode conductor, the installation must comply with the requirements of the appropriate raceway article

27 250.66(A) Connections to Rod, Pipe, or Plate Electrode(s) A GEC that connects directly to a single or multiple rod, pipe, or plate electrode(s) in (A)(5) or (A)(7), and does not extend to a grounding electrode requiring a larger size conductor is not required to be larger than 6 AWG FIGURE 3-41 Connections to rod, pipe, or plate grounding electrodes, (A).

28 250.66(B) Connections to Concrete-Encased Electrodes A GEC that connects directly to a single or multiple concreteencased grounding electrode(s) in (A)(3), and does not extend to a grounding electrode requiring a larger size conductor is not required to be larger than a 4 AWG copper wire FIGURE 3-42 Grounding electrode conductor connections to concrete-encased electrodes, (B).

29 250.66(C) Connections to Ground Rings A GEC that connects directly to a ground ring grounding electrode described in (A)(4), and does not extend to a grounding electrode requiring a larger size conductor is not required to be larger than the ground ring conductor FIGURE 3-43 Grounding electrode conductor connections to ground ring electrodes, (C).

30 250.68(C)(1) Grounding Electrode Connections Interior metal water piping that is electrically continuous with a metal underground water pipe electrode and is located not more than 5 ft (1.52 m) from the point of entrance to the building shall be permitted to extend the connection to an electrode(s). Interior metal water piping located more than 5 ft (1.52 m) from the point of entrance to the building shall not be used as a conductor to interconnect electrodes of the grounding electrode system.

31 250.68(C)(1) Exception Exception: In industrial, commercial, and institutional buildings or structures, if conditions of maintenance and supervision ensure that only qualified persons service the installation, interior metal water piping located more than 5 ft. (1.52 m) from the point of entrance to the building shall be permitted as a bonding conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor, if the entire length, other than short sections passing perpendicularly through walls, floors, or ceilings, of the interior metal water pipe that is being used for the conductor is exposed.

32 FIGURE 3-46 Water pipe grounding electrode exception, (C)(1), Exception.

33 250.68(C)(2) Metal Structural Frame The metal structural frame of a building is permitted to be used as a conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor Hold-down bolts securing the structural steel column that are connected to a concrete-encased electrode that complies with (A)(3) and is located in the support footing or foundation shall be permitted to connect the metal structural frame of a building or structure to the concrete encased grounding electrode. The hold-down bolts shall be connected to the concreteencased electrode by welding, exothermic welding, the usual steel tie wires, or other approved means.

34 FIGURE 3-47 Metal frame of a building is permitted as a bonding means or a grounding electrode conductor if grounded properly but is not a grounding electrode.

35 Connection to Rebar-Type Grounding Electrodes (C)(3) (3) A rebar-type concrete-encased electrode installed in accordance with (A)(3) with an additional rebar section extended from its location within the concrete to an accessible location that is not subject to corrosion shall be permitted for connection of grounding electrode conductors and bonding jumpers. The rebar extension shall not be exposed to contact with the earth without corrosion protection.

36 250.68(C)(3)

37 Service Raceways and Enclosures, Exception Metal components in a run of PVC conduit that are isolated from contact by a minimum cover of 18 in. are not required to be connected to the grounded system conductor, supply side bonding jumper, or grounding electrode conductor FIGURE 4-2 Grounding or bonding not required for isolated metal components, Exception.

38 Bonding for Communication Systems Communication system bonding is required to be connected in accordance with (A) or (B).

39 250.94(A) The Intersystem Bonding Termination Device (1 of 4) An intersystem bonding termination (IBT) for connecting intersystem bonding conductors is required to be provided external to enclosures at the service equipment or metering equipment enclosure and at the disconnecting means for any additional buildings or structures. If an IBT is used, it is required to comply with the following (next slides):

40 250.94(A) The Intersystem Bonding Termination Device (2 of 4) 1. Be accessible for connection and inspection 2. Consist of a set of terminals with the capacity for connection of not less than three intersystem bonding conductors 3. Not interfere with opening the enclosure for a service, building or structure disconnecting means, or metering equipment

41 250.94(A) The Intersystem Bonding Termination Device (3 of 4) 4. At the service equipment, be securely mounted and electrically connected to an enclosure for the service equipment, to the meter enclosure, or to an exposed nonflexible metallic service raceway, or be mounted at one of these enclosures and be connected to the enclosure or to the grounding electrode conductor with a minimum 6 AWG copper conductor

42 250.94(A) The Intersystem Bonding Termination Device (4 of 4) 5. At the disconnecting means for a building or structure, be securely mounted and electrically connected to the metallic enclosure for the building or structure disconnecting means, or be mounted at the disconnecting means and be connected to the metallic enclosure or to the grounding electrode conductor with a minimum 6 AWG copper conductor 6. The terminals shall be listed as grounding and bonding equipment (UL-467)

43 FIGURE 5-12 Intersystem bonding for communication systems,

44 250.94(A) Exception: Bonding for Existing Buildings or Structures (1 of 2) Exception: In existing buildings or structures, an accessible means external to enclosures for connecting intersystem bonding and grounding electrode conductors shall be permitted at the service equipment and at the disconnecting means for any additional buildings or structures by at least one of the following means

45 250.94(A) Exception: Bonding for Existing Buildings or Structures (2 of 2) 1. Exposed nonflexible metallic raceways 2. An exposed grounding electrode conductor 3. Approved means for the external connection of a copper or other corrosion-resistant bonding or grounding electrode conductor to the grounded raceway or equipment

46 250.94(B) Other Means (B) Other Means. Connections to an aluminum or copper busbar not less than ¼ in. thick 2 in. wide (6 mm thick 50 mm wide) and of sufficient length to accommodate at least three terminations for communication systems in addition to other connections. The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector. If aluminum busbars are used, the installation shall also comply with (A). Exception to (A) and (B): Means for connecting intersystem bonding conductors are not required where communications systems are not likely to be used.

47 250.94(B) Other Means

48 (F) Conductors in Parallel For circuits of parallel conductors as permitted in (H), equipment grounding conductors are required to be installed in accordance with (1) or (2)

49 (F)(1)(a) Conductors in Parallel in Single Raceway or Cable Tray (a) Single Raceway or Cable Tray. If conductors are installed in parallel in the same raceway or cable tray, a single wire-type conductor shall be permitted as the equipment grounding conductor. The wire-type equipment grounding conductor shall be sized in accordance with , based on the overcurrent protective device for the feeder or branch circuit. Wire-type equipment grounding conductors installed in cable trays shall meet the minimum requirements of (B)(1)(c). Metal raceways or auxiliary gutters in accordance with or cable trays complying with (B) shall be permitted as the equipment grounding conductor.

50 (F)(1)(a) Conductors in Parallel (in single raceway) FIGURE 6-27 Sizing equipment grounding conductor for a circuit with parallel conductors in a single raceway, (F)(1)(a).

51 (F)(1)(b) Conductors in Parallel in Multiple Raceways (b) Multiple Raceways. If conductors are installed in parallel in multiple raceways, wiretype equipment grounding conductors, where used, shall be installed in parallel in each raceway. The equipment grounding conductor installed in each raceway shall be sized in compliance with based on the overcurrent protective device for the feeder or branch circuit. Metal raceways or auxiliary gutters in accordance with or cable trays complying with (B) shall be permitted as the equipment grounding conductor.

52 (F)(1)(b) Conductors in Parallel in Multiple Raceways FIGURE 6-28 Sizing equipment grounding conductor for a circuit with parallel conductors in multiple raceways, (F)(1)(b).

53 (F)(2)(a) Conductors in Parallel, Multiconductor Cables (a) If multiconductor cables are installed in parallel, the equipment grounding conductor(s) in each cable shall be connected in parallel. FIGURE 6-29 General requirement for connecting equipment grounding conductors for multiconductor cables that have circuit conductors that are connected in parallel (F)(2)(a).

54 (F)(2)(b) Conductors in Parallel, Multiconductor Cables (b) If multiconductor cables are installed in parallel in the same raceway, auxiliary gutter, or cable tray, a single equipment grounding conductor that is sized in accordance with shall be permitted in combination with the equipment grounding conductors provided within the multiconductor cables and shall all be connected together.

55 (F)(2)(b) Conductors in Parallel, Multiconductor Cables FIGURE 6-30 Provision for external equipment grounding conductor that supplements standard size equipment grounding conductor in multiconductor cables that are connected in parallel and installed in a raceway, auxiliary gutter, or cable tray (F)(2)(b).

56 (F)(2)(b) Conductors in Parallel, Multiconductor Cables Fault-current will be shared by all equipment grounding conductor paths in inverse proportion to the impedance of the individual path. FIGURE 6-31 Sizing equipment grounding conductor for four 200-ampere cables that have conductors connected in parallel (F)(2)(b).

57 (F)(2)(d) Equipment Grounding Conductor in Multiconductor Cables Except as provided in (F)(2)(b) for raceway or cable tray installations, the equipment grounding conductor in each multiconductor cable shall be sized in accordance with based on the overcurrent protective device for the feeder or branch circuit.

58 Cengage October 2017

59 Wiring Residential Series Written by Phil Simmons & Ray C. Mullin Includes Residential Construction Code Simulations Date

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61 Date

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