Quik Talk
Last update April 18, 2002

In 1994 after being an electrical inspector for more than four years, question after question was asked about swimming pools and other questions on code, so I decided to write down the answers and hand them out. The first Quik Talk article I wrote was about ground rods at a pool site. It went over well with inspectors and contractors, so I decided to continue with the Quik Talk.


Mr. D Meadows: April 6, 2002


Reguarding your question on the size of the ground rod, please go to Article 250-52 Made and other electrodes. 1999 NEC

Where none of electrodes specified in Section 250-50 is availble, one or more of the (made) electrodes specified in (b) through (d) shall be used.

Since your question is on the ground rods, let's go down to 250-52(c)(1) and (c)(2). Rod and pipe electrodes shall not be less than 8 ft (2.44 m) in length, shall consist of the following materials, and shall be installed in the following manner.:

Electrodes of pipe or conduit shall not be smaller than 3/4 in. trade size and, where of iron or steel ,shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.

Electrodes of rods of iron or steel shall be at least 5/8 in. (15.87 mm) in diameter. Stainless steel rods less than 5/8 in. (15.87 mm) in diameter, norferrous rods, or their equivalent (such as copper) shall be listed and shall not be less than 1/2 in. (12.7 mm) in diameter.

The question on using the 1/2 in galvanized ground rod would be no. This section only allowed the stainless steel rod, nonferrous rod or the equivalent to be reduced, not the galvanized iron rod to 1/2 in. I can not speak any other Authority Having Jurisdicition, but it shall be a violation of the 1999 and 2002 NEC. Also you can't cut 8 ft. rods in half or install rods less than 8 ft.

ED STUBBS

GROUND RODS


How many ground rods are required around a swimming pool? This question is asked at least a hundred times by contractors and electrical inspectors alike. Well, if you said one or more, you are incorrect.


Through the years, Contractors, Engineers and Inspectors have required ground rods to be from one to several around a pool. Some have required them at every Conner of the pool. Some require them at every ladder, steps, motors and at any metal parts. What is the reason for this obsession with ground rods? Protection from lighting? Mud slides? To stabilize the pool from moving or hold the pool grid still? What? Some say it is to ground the pool. Well, pull your pants back up, get your hands out of your pockets and swallow that tobacco and tell me that a pool that is 60 ft long, 20 ft wide and 10 ft deep is not a better ground than 10 ground rods 5/8" X 8' driven 8 ft into the earth!


First, let's clear up the understanding of a ground rod and bonding. The sole purpose of a ground rod is to intentionally ground an electrode system to the earth from a system that intentionally carries a current and a voltage to the building or structure. This is covered in Article 250-50 Grounding Electrode Systems. Under the definition of grounded, effective; it states, "Intentionally connected to the earth through a grounded connection or connections of sufficiently low impedance and having sufficient current carrying capacity to prevent the build-up voltages that may result in undue hazards to connected equipment or persons." Other definitions follow with grounded conductors. Since we're not using a grounded electrode system, we shall move onto the word Bonding.


Definition of bonding: "The permanent joining of metallic parts to form an electrically conductive path that will assure electrical continuity and the capacity to conduct safely any current likely to be imposed." Under Article 680-22, the heading is bonding not grounding. Article 680-22(a) states "The following parts shall be bonded together." (1-6). Article 680-22(b) Common bonding grid."The parts specified in (a) shall be connected to a common bonding grid with a solid copper conductor, insulated, covered, or bare, not smaller than No. 8. Connection shall be made by exothermic welding or by pressure connectors or clamps that are labeled as being suitable for the purpose and are of the following material: stainless steel, brass, copper, or copper alloy. The common bonding grid shall be permitted to be any of the following." (1-4). Article 680-22, first paragraph was an (FPN) during the 1993 NEC but became code in 1996 NEC Addition. States: " It shall not be the intent of this section to require that the No. 8 or larger solid copper bonding conductor to be extended or attached to any remote panelboard, service equipment, or any electrode, but only that it shall be employed to eliminate voltage gradients in the pool area as prescribed."


The primary purpose of bonding is to ensure that voltage gradients in the pool area are eliminated. The revised wording of Section 680-22 in the 1999 Code makes it clear that the No. 8 conductor is only for elimination of the voltage gradient in the pool area and is not required to provide a path for fault current that may occur as a result of electrical equipment failure.


Hopefully this will clear up any misconceptions on requiring ground rods at a pool. Simply say, "The pool shall be bonded, not grounded." (Nov 10, 1994)


EQUIPMENT GROUND AND GROUNDING ELECTRODE


What is the difference between an Electrode and an Equipment Ground? If there isn't a difference, why are there two names for them? Are they both grounded or bonded together, or separate?


Well, basically, the only difference is the size and location of the (conductor or conductors) that limit a fault to ground. First, let's understand the word "Grounded" Definition of grounded: "Connected to the earth or to some conducting body that serves the place of earth." Grounded effectively: "Intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current carrying capacity to prevent the buildup of voltages that may result in undue hazards to connected equipment or persons" So what is the difference between an electrode and equipment ground? Simple, electrodes don't have overcurrent protection and are sized to the phase conductor(s) ahead of the main. The equipment ground protects the equipment by means of an overcurrent device sized for the protection of the conductors and the equipment down stream.


Article 250-81(1996) 250-50(1999) is your Grounding Electrode System which connects all current carrying electrodes, metals, water pipes, steel structures, and equipment grounds to a common bond like the chassis of an engine. Faults can dissipate in all directions with little or no damage to equipment or injury to a person(s). Since the phase conductors don't have overcurrent protection ahead of the main, the electrode system is required to be sized from table 250-94(1996), 250- 66(1999)NEC by the size of the phase conductor(s) to safely handle the fault current caused by one or more of the phase conducts to ground or a short phase to phase.


Now once you get pass the main, your grounded system is called Equipment Grounding. Why call it that? Well, now it is protecting (equipment.) The definition of equipment: "A general term including material, fittings, devices, appliances, fixtures, apparatus and the like used as a part of, or in connection with, an electrical installation. Since all equipment is required to be protected by overcurrent protection, the fault that can be imposed are going to be at a lower (SCA) short circuit ampacity then ahead of the main. So now the equipment ground shall be sized to meet the overcurrent protection used". Table 250-95(1995) 250-66(1999). Shows the conductor sizes in copper in copper and aluminum.


It is very important to know what an electrode is, and an equipment ground, so proper sizing will be achieved for your sake and the equipment. Jan 15,1996


CONDUIT BODY (LB'S)


Can a standard 2 inch conduit body (LB) with a 10 inch removable cover be used to carry 4 4/0 THHN conductors?


Yes. With only one exception under Article 370-28(a)(2)exp, you can use any size LB that meets the size of the raceways maximum conductor fill.


First, let's clear up what "standard" conduit body is. Most manufactures are going to size their LB's to meet the minimum requirement of the conduit fill and minimum length or distance to make a bend or turn with conductors of No. 6 and smaller where 90 degree bends would be a clearance problem. So, the LB opening is not so crucial, and they very in lengths to meet the needs of the installer.


Article 370-28(a) states: "For raceways containing conductors of No.4 or larger, and for cables containing conductors of No. 4 or larger, the minimum dimensions of pull or junction boxes installed in a raceway or cable run shall comply with the following:" (2) Angle or U Pulls."Where splices, or where angle or U pulls are made, the distance between each raceway entry inside the box and the opposite wall of the box shall not be less than six times the trade diameter of the largest raceway in a row" The exception pertains to a box and conduit body commonly known as an LB. The exception states: Where a raceway or cable entry is in the wall of a box or conduit body opposite a removable cover, the distance from that wall to the cover shall be permitted to comply with the distance required for one wire per terminal in table 373-6(a)."Again, this exception allows for the LB opening of less than 6 times the raceway size. 370-28(a)(3),also allows for the LB opening of less than 6 times under the following conditions: (3) "Boxes or conduit bodies of dimensions less than those required in (a)(1) and (a)(2) shall be permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill (of conduits or tubing being used) permitted by Table 1 of Chapter 9, provided the box or conduit body has been approved for and is permanently marked with the maximum number and maximum size of conductors permitted."


Basically, you will find that the manufactures will now label their LB's larger than 3 conductors and of any maximum size. Article 370-28 does by all means serve as an intent in this code and a LB with more than 3 maximum conductor size would defeat the use of this code section. Table 1 Chapter 9 (FPN 1) and notes to tables. Example: You have a 2 inch LB that is marked "maximum 3 4/0", and the removable cover is 9 inches long. You want to install 4 4/0 THHN conductors because Table 4 and 5 allows a 2 inch raceway, but the LB cannot be used unless the cover opening is 12 inches. 4 3/0 also will not be acceptable because it requires a 2 inch raceway and a 12 inch cover. If you install 4 1/0 conductor, you can reduce your LB opening to 1 X 6=9 inches.


As you can see, with conductors larger than No. 6 AWG, the NEC is enforcing the bending radius and not the conduit fill in cubic inches. Other conduit bodies called Mogul LB's, also may not meet the minimum requirements of Article 370-28, if it is not stamped on the Mogul or meets the minimum opening required for 6 times the raceway. Also, note that the conduit bodies marked LL and LR's do not meet the requirements of the exception, stating from the conduit wall to opposite to a removable cover. If you can't see through the short end of the LB to the removable cover, than it shall be 2 times the raceway size. Since the opening is to the right (LR) or left (LL) of the opposite wall, they are not acceptable. Remember, the larger the conductors, the larger the bending radius and space requirements. (Jan 13, 1995)


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This domain ED STUBBS.COM is in no way part of or connected to in any way, form or fashion with The City of Atlanta. The expressed opinions are not that of any political or public holding officials or city council governing rules and regulations over the City of Atlanta. The opinions also do not reflect on any local cities, counties, states or federal government on their rules and regulations, and / or city ordinances, but to show contractors, electricians, engineers and inspectors that may need clairity and understanding of The National Electrical Code. (NEC)


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