11/13/2018 1 MEA 2017 NEC Grounding and Bonding Part 4 2-hour class presented by Minnesota Electrical Association This seminar will satisfy the 2-hour electrical code training for electricians required by the State of Minnesota. Minnesota Electrical Association 1 Acknowledgements Some material and illustrations presented are with permission of Cengage Learning from: Electrical Grounding and Bonding 2014 by Phil Simmons The National Electrical Code (NEC) ® is: Document 70 from the National Fire Protection Association (NFPA)
Transcript
11/13/2018
1
MEA 2017 NECGrounding and Bonding
Part 4
2-hour class presented by
Minnesota Electrical Association
This seminar will satisfy the 2-hour electrical code training for electricians required by the State of Minnesota.
Minnesota Electrical Association 1
Acknowledgements
Some material and illustrations presented are with permission of Cengage Learning from: Electrical Grounding and Bonding 2014 by Phil Simmons
The National Electrical Code (NEC)® is: Document 70 from the National Fire Protection
Association (NFPA)
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Objectives:
Equipment required to be grounded that is fastened in place or connected by permanent wiring methods that is connected to an equipment grounding conductor
Types of acceptable equipment grounding conductors
Identification requirements for equipment grounding conductors
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Objectives:
Installation requirements for equipment grounding conductors
The minimum size of equipment grounding conductors
Rules for continuity of equipment grounding conductors
Means of identification of wiring device terminals
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Part VI: Equipment grounding and Grounding Conductors
250.110 Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
Exposed normally non–current-carrying metal parts of fixed equipment supplied by or enclosing conductors or components that are likely to become energized are required to be connected to the equipment grounding conductor under any of the following conditions:
(1) If within 8 ft (2.5 m) vertically or 5 ft (1.5 m) horizontally of ground or grounded metal objects and subject to contact by persons
(2) If located in a wet or damp location and not isolated ----Continued---
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250.110 Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
(3) If in electrical contact with metal(4) If in a hazardous (classified) location as covered
by Articles 500 through 517(5) If supplied by a wiring method that provides an
equipment grounding conductor, except as permitted by 250.86 Exception No. 2 for short sections of metal enclosures
(6) If equipment operates with any terminal at over 150 volts to ground
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250.110 Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
• Exception No. 1: If exempted by special permission, the metal frame of electrically heated appliances that have the frame permanently and effectively insulated from ground shall not be required to be grounded.
• Exception No. 2: Distribution apparatus, such as transformer and capacitor cases, mounted on wooden poles at a height exceeding 2.5 m (8 ft) above ground or grade level shall not be required to be grounded.
• Exception No. 3: Listed equipment protected by a system of double insulation, or its equivalent, shall not be required to be connected to the equipment grounding conductor. Where such a system is employed, the equipment shall be distinctively marked.
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250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
Except as permitted in 250.112(F) and (I) (as follows) , (following sections)) exposed, normally non–current-carrying metal parts of equipment described in 250.112(A) through (K) (as follows) , and normally non–current-carrying metal parts of equipment and enclosures described in 250.112(L) and (M) (as follows), shall be connected to an equipment grounding conductor, regardless of voltage.
(A) Switchgear and Switchboard Frames and Structures. Switchgear and Switchboard frames and structures supporting switching equipment, except frames of 2-wire dc switchgear or switchboards where effectively insulated from ground.
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250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
(B) Pipe Organs. Generator and motor frames in an electrically operated pipe organ, unless effectively insulated from ground and the motor driving it.
(C) Motor Frames. Motor frames, as provided by 430.242. (grounding of stationary motors )
Specific requirements for grounding motors and related equipment can be found in Article 430, Part XIII.
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250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
(D) Enclosures for Motor Controllers. Enclosures for motor controllers unless attached to ungrounded portable equipment.
(E) Elevators and Cranes. Electric equipment for elevators and cranes.
(F) Garages, Theaters, and Motion Picture Studios. Electric equipment in commercial garages, theaters, and motion picture studios, except pendant lampholders supplied by circuits not over 150 volts to ground.
(G) Electric Signs. Electric signs, outline lighting, and associated equipment as provided in Article 600.
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250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
(I) Power-Limited Remote-Control, Signaling, and Fire Alarm Circuits. Equipment supplied by Class 1 circuits is required to be grounded unless operating at less than 50 volts. Equipment supplied by Class 1 power-limited circuits, Class 2, and Class 3 remote-control and signaling circuits, and by fire alarm circuits, are required to be grounded if the system is to be grounding by Part II or Part VIII of Article 250.
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250.112(J) Grounding Luminaires
Luminaires with exposed conductive parts are generally required to be grounded in accordance with Part V of Article 410
Luminaires: Exposed metal parts are required to be connected to an equipment grounding conductor or be insulated from the equipment grounding conductor and other conducting surfaces or be inaccessible to unqualified personnel.
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410.44 General
Luminaires and lighting equipment are required to be mechanically connected to an equipment grounding conductor as specified in 250.118 that is sized in accordance with 250.122 if of the wire type.
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410.44 Ex. No. 1 Made of Insulating Material
Luminaires directly wired or attached to outlets supplied by a wiring method that does not provide a ready means for grounding attachment to an equipment grounding conductor are required to be made of insulating materials and have no exposed conductive surfaces.
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410.44 Ex. No. 2 Replacement Luminaires
Replacement luminaires (fixtures) are permitted to be grounded in accordance with 250.130(C)
If no equipment grounding conductor exists at the outlet, replacement luminaires are permitted to be GFCI protected rather than being connected to an equipment grounding conductor
Listing requirements may mandate connecting to equipment grounding conductor. 110.3(B)
250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
(K) Skid Mounted Equipment. Permanently mounted electrical equipment and skids shall be grounded with an equipment bonding jumper sized as required by 250.122.
(L) Motor-Operated Water Pumps. Motor-operated water pumps, including the submersible type are required to be connected to the equipment grounding conductor.
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250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
(M) Metal Well Casings. If a submersible pump is used in a metal well casing, the well casing must be bonded to the pump circuit equipment grounding conductor.
Conditions as in items 1-4 the exposed non-current carrying parts of equipment will be connected to an equipment grounding conductor
1) Hazardous locations2) Operating over 150 Volts to ground - with
exceptions 3) In residential occupancies - see list4) Other than residential occupancies - see list
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250.116 Non-electrical equipment
The metal parts of equipment shall be connected to ground
1) Frames and tracks of electrically operated hoists and cranes
2) Frames of elevators that have electrical conductors to the cars (hydraulic elevators)
3) Hand operated metal ropes or cables of electric elevators
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250.118 Types of Equipment Grounding Conductors
• A copper, aluminum, or copper-clad aluminum conductor. This conductor is generally permitted to be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
• An insulated equipment grounding conductor is required by several NEC sections
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250.118 Types of Equipment Grounding Conductors
(2) Rigid metal conduit
(3) Intermediate metal conduit
(4) Electrical metallic tubing
◦ Good workmanship is essential in providing an effective fault-current path◦ The conduit or tubing carry fault current◦ Loose connections can interrupt the fault path
or cause arcing or sparking
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RMC, IMC and EMT
No maximum length to function as an equipment grounding conductor is given in the NEC
Maximum “effective” length can be calculated using GEMI™ software o Set up software using values for fault clearing
characteristics of overcurrent device
Table 6-1 (next slide) has effective lengths for circuit breaker and fuse OCP
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TABLE 6-1
If Overcurrent trips at: 5 X rated current for fault then use 5X, if 2 times rated current then 2X
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250.118(5) Listed FMC
Conduit is terminated in listed fittings
Circuit conductors have OCP max 20A
Combined length not more than 6 ft
The size of the conduit does not exceed 1-1/4” trade size
EGC required if installed for flexibility to minimize transmission of vibration
This construction of corrugated tube Type MC cable is suitable as an equipment grounding conductor, as a bare equipment grounding conductor if listed and identified.
392.60 Grounding and Bonding. Metallic cable trays are permitted to be used as equipment grounding conductors if continuous maintenance and supervision ensure that qualified persons service the installed cable tray system and the cable tray complies with provisions of this section.
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250.118(12) Cablebus
Cablebus framework as permitted in 370.60(1). “Cablebus framework, where bonded as required by Article 250, shall be permitted as the equipment grounding conductor for branch circuits and feeders.”
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Cable Tray
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250.118(13) Other Raceways
Other listed electrically continuous metal raceways and listed auxiliary gutters
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250.118(14) Surface Metal Raceways
Surface metal raceways is listed for grounding ---As per UL when installed per specifications
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250.119 Identification of Equipment Grounding Conductors
Permitted to be bare, covered or insulated
Covered or insulated conductors to have continuous finish that is either green or green with a yellow stripe
Not permitted to be used as grounded or ungrounded conductor
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250.119 Exception # 1
Power limited Class 2 or Class 3 cables, power-limited fire alarm cables, or communications cables containing only circuits operating at less than 50 volts are permitted to use a conductor with green insulation for other than equipment grounding purposes
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250.119 Exception # 2
Flexible cords having an integral insulation and jacket without an equipment grounding conductor shall be permitted to have a continuous outer finish that is green. (Christmas Tree wire, extension cords)
Informational Note: An example of a flexible cord with Integral-type insulation is Type SPT-2, 2 conductor.
When looking at the two numbers for the zip cord, SPT-1 wire has an insulation thickness of 0.030″ and 18/2, SPT-2 has insulation that is 0.045″ thick.
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250.119 Exception #3
Conductors with green insulation shall be permitted to be used as ungrounded signal conductors where installed between the output terminations of traffıc signal control and traffıc signal indicating heads.
Signaling circuits installed in accordance with this exception shall include an equipment grounding conductor in accordance with 250.118.
Wire-type equipment grounding conductors shall be bare or have insulation or covering that is green with one or more yellow stripes.
250.120(B) Aluminum and Copper-Clad Aluminum Conductors
Bare or insulated are permitted
Bare conductors are not permitted in direct contact with masonry or the earth or where subject to corrosive conditions
Aluminum or copper-clad aluminum conductors are not permitted to be terminated within 18 in. of the earth
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250.120(C) EGCs Smaller Than #6 AWG
Protect from physical damage by a raceway or cable armor except where run in hollow spaces of walls or partitions where not subject to physical damage or protected from physical damage
An equipment grounding conductor (EGC) shall not be used as a grounding electrode conductor (GEC).
Except: See next slide
Sizing and installation requirements differ significantly.
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250.121 Use of Equipment Grounding Conductor
Exception: A wire-type equipment grounding conductor installed in compliance with 250.6 A (no objectionable currents) and the applicable requirements for both the equipment grounding conductor and the grounding electrode conductor in Parts II, III, and VI of this article shall be permitted to serve as both an equipment grounding Conductor and a grounding electrode conductor.
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250.122 Size of Equipment Grounding Conductors
Size in accordance with Table 250.122
Not required to be larger than the circuit conductors
If cable tray, raceway or cable armor or sheath is used as the equipment grounding conductor, it must be installed to provide an effective ground-fault return path as provided in 250.4(A)(4) or (B)(5)
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Table 250.122 Minimum Size of Equipment Grounding Conductor for Grounding Raceway and Equipment
Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, Conduit,
Increasing Size of EGC for Available Short-Circuit Current
The size of the equipment grounding conductor in Table 250.122 is shown to be the “Minimum Size.”
It may need to be increased in size using data such as Table P-32-382 from the Insulated Cable Engineers Association
Do not exceed thermal damage curve for equipment grounding conductor
The equipment grounding conductor must be large enough so it can carry the fault current delivered by the system until the overcurrent device opens
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Insulated Cable Engineers Association (ICEA) P-32-382
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250.122(B) Increased in Size
If ungrounded conductors are increased in size, wire type equipment grounding conductors, where used, must be increased proportionately by circular mil area
The phase conductors are typically increased in size for:◦ Excessive voltage drop◦ High ambient temperatures◦ More than 3 current-carrying conductors in a
raceway or cable
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Example
200-ampere feeder installation◦ Normal size – 3/0 AWG copper◦ Installed size 300 kcmil for losses
300,000 ÷ 167,800 = 1.788 × bigger ◦ (167,800 = cm area of 3/0 conductor)
Required EGC Table 250.122 = 6 AWG Cm area of 6 AWG in Table 8, Chapter 9 = 26,240 26,240 × 1.788 = 46,917 cm Next standard size in Table 8 of Chapter 9 = 3 AWG
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250.122(C) Multiple Circuits
Size single equipment grounding conductor for multiple circuits based on the largest overcurrent device for contained conductors
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250.122(D) Motor Circuits
Equipment grounding conductors must be installed in accordance with (D)(1) or (D)(2)
(D)(1) The equipment grounding conductor is required to be not smaller than the size determined from Table 250.122 based on the rating of the branch circuit, short circuit and ground fault protection
BUT : The equipment grounding conductor is not required to be larger than the circuit conductors
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Motor Circuits
Size per Table 250.122 for the rating of branch-circuit, short-circuit, and ground-fault protective device
16.7 A × 1.25 = 20.9 amperes (minimum conductor size)
Table 310.15(B)(16) = 12 AWG (25 amperes)
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Example: Motor Circuits
Circuit breaker used as BC, SC and GF protection permitted to be 250% of FLA or 16.7 x 2.5 = 41.8 A
Next standard OC device is 45 A
Table 250.122, EGC required to be 10 AWG- BUT:
EGC permitted to be same as circuit conductors or 12 AWG
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250.122(D)(2) Motor Circuits
If the overcurrent device consists of an instantaneous trip circuit breaker or a motor short-circuit protector, the equipment grounding conductor is required to be sized not smaller than given by 250.122(A) using the maximum permitted rating of a dual-element time-delay fuse selected for branch-circuit short-circuit and ground-fault protection in accordance with 430.52(C)(1) Exception No. 1. (Next higher size)
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Here’s How50 HP, 460-Volt, 3-Phase Motor
FLA from Table 430.250 = 65 A
Conductor minimum 125 % = 65 × 1.25 = 81 A
Select 4 AWG (85 A) Table 310.15(B)(16)
FLA × 175 % for BC, SC & GF = 65 × 1.75 = 113.8 A
Round up to 125 A overcurrent device
Select 6 AWG EGC from Table 250.122
70# 6 EGC with #4 ungrounded conductors 70
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250.112(F) Conductors in Parallel
If conductors are installed in parallel in multiple raceways as permitted in 310.10(H), equipment grounding conductors where used, are required to be installed as per 1-2 below.
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250.122 (F) NEW (1) Parallel Conductors in Raceways….
If EGC conductors are installed in parallel in raceway or cable tray, a single wire type EGC may be installed based on 250.122. (raceways and cable trays may serve as the EGC as per 250.118 or 392.60(B)
If EGC conductors are installed in parallel in multiple raceways, the conductors are based on 250.122 and the full size is installed in each raceway. Raceways and cable trays may be used for the EGC.
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250.122 (F) NEW (2) Multiconductor Cables
(a) If multi-conductor cables are installed in parallel, the EGC conductors are also installed in parallel
(b) If multi-conductor cables are installed in a common raceway, a single EGC per .122 is permitted and connected in parallel with the cable EGC.
(c) EGC conductors in cable trays meet 392.(d) Where multi-conductor cables installed in
parallel, the EGC in each cable shall be based on .122 for the OCP of the total circuit
FPN: One example of a symbol used to identify the termination point for an equipment grounding conductor
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Art 250 Part VII Methods of Equipment
Grounding
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Objectives:
Equipment grounding conductor connections
Methods permitted for non-grounding receptacle replacement and branch circuit extensions
Rules for equipment fastened in place or connected by permanent wiring methods
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Objectives:
Grounding frames of ranges, dryers and associated equipment
Use of grounded circuit conductor for grounding equipment
Connecting receptacle grounding terminals Bonding of general-use snap switches Continuity and attachment of equipment
grounding conductors to boxes
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250.130 Equipment Grounding Conductor Connections
Equipment grounding conductor connections at separately derived systems made per 250.30(A)(1)
Equipment grounding conductor connections at service equipment made per 250.130(A) or (B)
Replacement of receptacles and branch-circuit extensions that do not have equipment grounding conductors permitted as in250.130(C) (this article)
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250.130(A) For Grounded Systems
Bond the equipment grounding conductor to the grounded service conductor and the grounding electrode conductor
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250.130(B) For Ungrounded Systems
Bond the equipment grounding conductor to the grounding electrode conductor
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250.130(C) Non-grounding Receptacle Replacement or Branch-Circuit Extensions
The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension is permitted to be connected to any of the following:
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For ungrounded systems, the grounding terminal bar at the service
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250.130(C) Non-grounding Receptacle Replacement or Branch-Circuit Extensions
The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension is permitted to be connected to any of the following:
(1) Any accessible point on the grounding electrode system as described in 250.50
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
(4) An equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates
(5) For grounded systems, the grounded service conductor within the service equipment enclosure
(6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure
Caution: Many types of equipment are required to be grounded by NEC rules or by manufacturer product listing
If equipment or appliance is required to be grounded, GFCI protection is not permitted in lieu of grounding
Must comply with NEC 110.3(B)
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250.130(C) Branch-Circuit Extensions
Applies where the existing branch circuit does not contain an equipment grounding conductor
An equipment grounding conductor is installed back to point permitted in 250.130(C)
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250.134 Equipment Fastened in Place
Unless grounded by connection to the grounded circuit conductor as permitted by 250.32, 250.140 and 250.142, the non-current-carrying parts of equipment, raceways and other enclosures, if grounded, must be grounded by one of the following methods.
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250.134(A) Equipment Grounding Conductor Types
By connection to any of the equipment grounding conductors recognized by 250.118
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250.134(B) With Circuit Conductors
By connection to the equipment grounding conductor contained within the same raceway, cable or otherwise run with the circuit conductors
Exception: The equipment grounding conductor is permitted to be run separately as provided in 250.130(C).
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250.136 Equipment Considered Effectively Grounded
Under the conditions specified in 250.136(A) and (B), the non-current-carrying metal parts of equipment is considered to be effectively grounded.
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250.136(A) Equipment Secured to Grounded Metal Supports
Electrical equipment secured to and in electrical contact with metal rack that is grounded by one of the means provided in 250.134
The structural metal frame of a building shall not be used as the required EGC.
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250.140 Frames of Ranges and Clothes Dryers (New circuits)
Required to be grounded in accordance with 250.134 or 250.138
For appliances requiring a neutral or grounded conductor, a four-wire circuit is required
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250.140 Frames of Ranges and Clothes Dryers (Existing circuits)
Permitted to ground to grounded circuit conductor if:
◦ The supply circuit is 120/240-V, 1-Ph, 3-wire or 208Y/120-V from a 3-Ph, 4-wire system
◦ (continued)
9797
250.140 Frames of Ranges and Clothes Dryers ( Exception- Existing circuits)
If no equipment grounding conductor is present in the in the outlet box, the frame of the appliance can be connected to the grounded conductor, if all of the following:
The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum
The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE cable and the branch circuit originates at the service (not a subpanel)
Grounding contacts of receptacles are bonded to the equipment
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250.140 Frames of Ranges and Clothes Dryers (Existing circuits)
Caution on relocating ranges or dryers where the circuit and receptacle is different from the appliance
A connection from the neutral to the frame is required for 3-wire branch circuits
• Isolate the neutral and connect the equipment grounding conductor to the frame if a 4-wire branch circuit is available
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250.142 Use of Grounded Circuit Conductor for Grounding Equipment
Supply side Service / derived system – grounded circuit conductor permitted to ground equipment:
• On the supply side or within the enclosure of the ac service disconnecting means
• On the supply side, or within the enclosure, of the main disconnecting means for separate buildings as provided in 250.32(B)
• For separately derived systems as provided in 250.30(A)(1)
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250.142 Use of Grounded Circuit Conductor for Grounding Equipment
Load side: Not generally permitted to ground equipment by the grounded conductor. Except as permitted:
• 250.30(A)(1) for separately derived systems• 250.32(B) Exception at building or structure• The frames of ranges and dryers as provided in
250.140
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250.142 Use of Grounded Circuit Conductor for Grounding Equipment
A listed exposed work cover is permitted to be the grounding and bonding means when:
• The device is attached to the cover with at least two fasteners that are permanent (such as a rivet) or have a thread locking or screw locking meansand
• The cover mounting holes are located on a flat non-raised portion of the cover
The isolated equipment grounding conductor is permitted to pass through one or more panelboards, boxes, wireways, or other enclosures without being connected to the enclosure. It must be terminated at nearest:
• Separately derived system (if the source)• Building disconnecting means• Service equipment
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250.146(D) Isolated Receptacles
Identified by an orange triangle on its face
Equipment grounding terminal is isolated fromany metal yoke as well asfrom the center terminalfor the cover plate
IN: Use of an isolated ground does NOT dismiss the requirement for the grounding of the raceway or the outlet box
250.148 Continuity and Attachment of Equipment Grounding Conductor to Boxes
If circuit conductors are spliced within a box or terminated on equipment within, or supported by a box, any equipment grounding conductor associated with the conductors must be spliced or joined in the box or to the box
250.148 Continuity and Attachment of Equipment Grounding Conductor to Boxes
Equipment grounding conductors associated with feeder conductors are permitted to pass through a pull box unbroken if the circuit conductors are not spliced within the box
One or more equipment grounding conductor brought into the box must be arranged so a connection can be made to any fitting or device in the box that requires grounding
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