Unit 231 Grounding Bonding Overcurrent Protection

NEC Article 250 Electrical System Grounding Sizing grounding conductors Sizing equipment grounds Proper Ground Installation

NEC Article 280 Surge Arresters

NEC Article 285 Transient Voltage Surge Suppressor

NEC Article 680 Swimming Pool Wiring Swimming Pool Grounding and Bonding

NEC Article 240 Overcurrent Conditions Overcurrent Protection

NEC Article 408 Switchboards and Panelboards

NEC Article 550 Mobile Homes Mobile Home Parks

NEC Article 551 Recreational Vehicles Recreational Vehicle Parks

NEC Article 552 Park Trailers

Code References ● Article 100 ● Article 240 ● Article 250 ● Article 280 ● Article 408 ● Article 490 ● Article 550 ● Article 551 ● Article 552 ● Article 680 ● Chapter 9 ● Section ● Section 215.2(D) ● Section (B) ● Section 645.5

Objectives Properly illustrate electrical equipment grounding, system grounding, and bonding. Specify when an electrical system is required to be grounded and which conductor must be grounded.

Determine the proper sizing for equipment grounding conductors, grounding electrode conductors, and bonding conductors. Contrast the different types of overcurrent conditions and their possible damage to equipment.

Discuss electrical faults and equipment interrupting ratings. Determine voltage drop on conductors and properly size conductors so as to limit voltage drop to acceptable levels.

Answer code related questions from NEC Articles 240, 250, 280, 408, 490, 550, 551, 552, and 680

Study Tip In the previous lessons you learned about the three memory techniques of “selection” “attention” and “association” The fourth technique is “repetition.” It is always necessary to go over material in order to retain it. In general, the more you go over it, the longer you will retain it. But you will have to use a lot less repetition if you utilize the other three memory techniques in conjunction with repeating the material.

NEC Article 250 Electrical System Grounding Sizing grounding conductors Sizing equipment grounds Proper Ground Installation

Electrical System Grounding – There are 5 reasons to ground systems and circuits : ● Lightning ● Line surges ● Unintentional contact with higher voltage lines ● Stabilizing the voltage to ground during normal operations ● Facilitate over-current device operation in case of ground fault on a solidly grounded system

Why Ground? – The grounded conductor of a grounded system establishes a low-impedance path for fault-current through the over-current protective device to limit the length of time a fault exists. – This low impedance path is to facilitate the operation of over-current devices. – Grounding is not just for protection against electrical shock

– This path to ground must be: ● Intentionally made ● Permanent ● Electrically continuous ● Large enough ampacity to conduct any fault current safely ● A low impedance path

– When grounding is improperly installed, the results can range from minor physical harm to even death to an individual, or costly damage to electrical equipment and/or property. – Improperly grounded electrical systems can operate for years with no problem until something goes wrong.

Definitions – Ground – a conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body in place of the earth. – Grounded – connected to earth or some conducting body that serves in place of the earth.

– Grounded conductor - a system or circuit conductor that is intentionally grounded – Grounding conductor - a conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes. – Main bonding jumper – the connection between the grounded circuit conductor and the equipment grounding conductor at the service. – Grounding Electrode conductor – the conductor used to connect the grounding electrode(s) to the equipment grounding conductor, to the grounded conductor, or both, at the service, or at the source of a separately derived system.

– Equipment grounding conductor – the conductor used to connect the non-current – carrying metal parts of equipment, raceways and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system. – Equipment bonding jumper – the connection between two or more portions of the equipment grounding conductor. – Bonding – the permanent joining of metallic parts to form an electrically conductive path that insures electrical continuity and the capacity to conduct safely any current likely to be imposed

Grounding Electrode – The term “grounding electrode” of an electrical installation is the way into earth for the electrons. Therefore, installing a grounding electrode in the earth means installing an electrical terminal to help the electrons travel into the earth. Since 1978, the NEC has required a grounding electrode system to be used because of the increased use of plastic water pipe. – Before that, steel or copper water pipe that was used was always looked upon as a very good grounding electrode.

– Responsibility number one of the grounding electrode system is to maintain zero potential between ground and non-current carrying metal parts of electrical equipment and enclosures. This can be accomplished by having an effectively grounded system, with special care given to maintaining continuity of the system’s equipment grounding conductors. Bonding all grounding electrodes together is an important step in maintaining a zero potential.

– One responsibility that is often wrongfully assigned to the grounding electrode is to carry the current to operate the over-current device. That is not the responsibility of the grounding electrode. – The ground fault path through the earth, through the grounding electrode to the over-current device is a very high impedance path. It will not allow nearly enough current flow for the operation of the over-current protective device.

TYPES OF GROUNDING ELECTRODE Article – – The following items (1-8) are types of grounding electrodes you need to know: – 1. Metal underground water pipe250.52(A)(1) ● Shall be metal and placed underground ● Shall be 10’ or more in length & can be a well casing ● Electrically continuous ● Located within 5’ of entrance to building ● Interior pipes not used as a grounding conductor

– 2) Metal frame of building (A)(2) ● A. This article recognizes effectively grounded building steel as a ground electrode ● B. When a metal pipe is the primary grounding electrode, then the building steel can be the supplemental grounding electrode

– 3) Concrete encased electrode (A)(3) ● A. Minimum #4 bare copper at least 20’ long or reinforcing rod ½ inch in diameter at least 20’ long, located within and near the bottom of a concrete foundation or footing. ● B. Also referred to as a Ufer Ground

– 4.) Ground RingArticle (A)(4)NEC ● Minimum #2 bare copper wire at least 20’ in length, 2 ½ “ in depth, in direct contact with earth and encircle the building or structure.

– 5) Ground Rod250.52(A)(5) ● A. This article states that the min. length of a copper ground rod is 8’ with a min diameter of ½ “. Rods of iron or steel are required to be a min of 5/8 “. ● B. The ground rod is a commonly used electrode ● C. The requirements for installation of rod and pipe electrodes are listed in Article (G), NEC 2005 ● Please review this article now.

– 6.) Pipe electrodes250.52(A)(5) ● Pipe electrodes must be galvanized or corrosive resistant pipe. - They must be at least 8’ in length, ¾ “ in diameter and driven to a depth of 8’.

– 7.) Plate electrodes250.52(A)(6) ● Must be 2 square feet, made of steel or iron, ¼” thick, or.06 “ thick if copper, buried at least 30” into the earth.

8.) Other local metal underground systems or structures250.52(A)(7) ● Other systems such as piping systems and Underground tanks, when present on the premises, are required to be bonded together.

Electrodes not permitted for grounding – Metal underground gas pipes – Aluminum electrode

Grounding Electrode Conductor The purpose of a grounding electrode conductor is to connect the grounding electrode with: ● 1. The grounded conductor ● 2. The equipment grounding conductor ● 3. The main bonding jumper

The grounding electrode conductor actually completes three grounding paths to the grounding electrode conductor as follows: ● 1. The path from the grounded conductor ● 2. The path from the equipment grounded conductor when a wire is used ● 3. The path for the main bonding jumper when raceways are used

According to Article , grounding electrode conductors can be copper, aluminum or copper clad aluminum. They shall resist corrosive conditions and be protected from corrosion. – They can be 1. solid 2. stranded 3. insulated 4. covered or bare.

– Article (C) states the basic rule for installing a grounded electrode conductor: ● 1. Do it un-spliced ● 2. If it cannot be done un-spliced, must use irreversible compression-type connectors listed for that purpose or use the exothermic welding process. ● Exception: allows sections of busbar to be bolted together to form a grounding electrode conductor.

Protecting against physical damage – Article (B) states “if the conductor is run in a metal raceway, it is required to be grounded at both ends to prevent damage by magnetic induction”. Article (A) states “if made of aluminum and installed outdoors, shall not be terminated within 18” of the earth.

Enclosures for grounding Article (E) – Metal enclosures for grounding electrode conductors shall be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting.

Types of Alternating Current Systems – The NEC divides alternating current systems into three groups as follows: ● 1. Group 1 – systems operating at less than 50 volts ● 2. Group 2 - systems operating at 50 to 1,000 volts ● 3. Group 3 - systems operating at 1Kv and over ● Reference Article (A), page 95 of the NEC ● Please look at this article for review of Group 1

Group 1 – systems operating at less than 50 volts – Most systems under 50 volts do not have to be grounded – If the system is supplied by a transformer and the transformer's supply is ungrounded, the secondary side of the transformer shall be grounded. – Where conductors are installed overhead outside a building, they are required to be grounded.

Group 2 – Systems at 50 to 1,000 volts – Article (B) and , page 95 of NEC – Review page 95, Article (B)(C)(D) &

– These systems: ● Most are required to be grounded; some are not (see ) ● Figure 8-20 illustrates the conductors that shall be grounded for the various systems listed in of the NEC as follows:

● 1. Single phase two wire systems 120 volt must have one conductor grounded. ● 2. Single phase 120/240 volt, 3 wire systems with a center tap of the secondary of a transformer shall be grounded. ● 3. The 3-phase, 120/208 or 480/277 volt, 4 wire system which is a wye-connected with wye point of the system used as a neutral conductor shall be grounded.

● 4. The 3-phase, 120/240 volt, 4 wire delta-connected system, where the mid-point of one phase is used as the neutral circuit conductor, is required to be grounded. The system is known as a high leg, wild leg or red leg delta. The reason it is called a high leg is that one phase has much higher voltage reading to ground. (in figure 8-20, this is item 5) ● 5. The delta connected, 3-phase, 3 wire system, normally 480 volt, with one phase conductor is grounded. The phase conductor that is grounded is a grounded conductor through- out the system. It is identified as a circuit grounded conductor using white, gray or three white stripes on an insulation other than green. A 480 volts corner grounded 3-phase system does not have a neutral, just a ground. (in figure 8-20, this is item 4)

Group 3 - Systems of 1,000V and over.. – Article (C )(D) page 95 - NEC ● (C) alternating current systems supplying mobile or portable equipment shall be grounded as specified in Article Please read this article. ● (D) separately derived systems as covered in (A) or (B) shall be grounded as specified in Please read this article.

I. Calculating the minimum size ground conductor – The basic rule for sizing the grounding electrode conductor for a grounded and ungrounded system is found in Article in the NEC. – The size of the grounding electrode conductor of an Alternating Current system is required to be not less than that in Table When sizing the grounding electrode conductor, it is sized according to the cross- sectional area of the service entrance conductors.

Alternate Methods for sizing grounding electrode conductor – There are three alternate methods to sizing the grounding electrode conductor using Table : – 1) Article (A) is for grounding electrode conductor for a rod, pipe or plate electrode. The sole connection to the electrode and the service equipment is not required to be larger than 6 AWG copper or 4 AWG aluminum.

● 2) Article (B) is for grounding electrode conductor where a concrete encased electrode is the sole connection to the grounding electrode. The grounding electrode conductor is not required to be larger than 4 AWG copper. ● 3) Article (C) is for grounding electrode conductor where a ground ring is the sole connection to the grounding electrode. The grounding electrode conductor is not required to be larger than the conductor used for the ground ring.

Grounded Conductor – Definition: a system or circuit conductor that is intentionally grounded. – The grounded electrical conductor is part of the overall grounding system and under fault conditions, it becomes an equipment grounding conductor from the service back to the source. – The grounded conductor installed in the service raceway is used as the equipment grounding conductor between the utility company and the service disconnecting means. An additional equipment grounding conductor is not required.

Sizing the Grounded (Neutral) Conductor – If the grounded conductor is used as a circuit conductor, it is sized according to Article 220 (branch circuit and feeder calculations). The grounded conductor can never be smaller than the grounding electrode conductor or required to be larger than the phase conductors. – Article (B)(1) basically states that the grounded conductor will be sized off Table when the size of the service entrance conductors is not larger than 1,100 kcmil copper or 1750 kcmil aluminum (refer to page 100 in the NEC)

● When the service entrance conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor shall be 12.5 percent of the largest phase conductor. ● Where the service phase conductors are paralleled in the same raceway, the size of the grounded conductor shall be based on the total cross-sectional area of any one phase.

● Where the service-entrance conductors are installed in two or more raceways, the grounded conductor is based on the size of the service-entrance conductors in each raceway. However, it is not permitted to be smaller than 1/0 AWG. This coordinates with Article which limits the smallest conductor in parallel to be 1/0 AWG.

Installing the Grounded Conductor – Article (A)(5), page 96 NEC ● The grounded conductor (neutral) connection is prohibited by Article (A)(5) to be made to any grounded circuit conductor on the load side of the service disconnecting means.

Main Bonding Jumper – Article (d), page 97 NEC ● Defining the Main Bonding Jumper – During a fault condition, the grounded circuit conductor becomes the equipment grounding conductor through the main bonding jumper. – Article 100 definition: Bonding Jumper, Main. The connection between the grounded circuit conductor and the equipment grounding conductor at the service.

– Article (D), page 97, Table , page 104 NEC 2005 ● Sizing the Main Bonding Jumper – Basic rule is to use Table The grounding electrode conductor table is also used for sizing the main bonding jumper. – The 12.5 percent rule applies for the main bonding conductor when the service phase conductors are larger than 1100 kcmil copper or 1750 aluminum – When using different material from the service entrance conductors, one could be copper and the other aluminum. The minimum size of the main bonding jumper will be equivalent in ampacity.

Equipment Grounding Conductor – Article (A), Article – Equipment Grounding conductor – is used to connect the non-current-carrying metal parts of equipment, raceways and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system.

The equipment grounding conductor plays no part in delivering current in an electrical lighting or power circuit. But it plays a very important part in ensuring safety in the grounding system. When there is a grounded system, the equipment grounding is connected to the grounded conductor and the grounding electrode conductor. When there is an ungrounded system and no grounded conductor, the equipment grounding conductor is connected to the grounding electrode conductor.

Article , Table ● Sizing the Equipment Grounding Conductor – Article states the equipment grounding conductor will be sized according to Table , based on the size of the largest over current device protecting the ungrounded conductors in a raceway.

Short Circuit The unintentional connection of two ungrounded conductors that have a potential difference between them. A short circuit also occurs when an ungrounded conductor is connected to a grounded conductor. The largest overcurrent results when a short circuit occurs. A short circuit is not an overload.

Ground Fault An unintentional connection between an ungrounded conductor and any grounded raceway, box, enclosure, fitting, etc. Ground faults can result in a large-magnitude current flow in the ground path. The amount of current that flows depends on the impedance of the ground path back to the source of power.