Article 110 Requirements for Electrical Installations
Article 250 Grounding
Article 334 Nonmetallic-Sheathed Cables: Types NM, NMC and NMS
Article 422 Appliances
Article 517 Health Care Facilities
Article 680 Swimming Pools, Fountains and Similar Installations
Grounding a feeder circuit to a second building
Q:How do I size a feeder grounding conductor to a second building or structure that is supplied from a common service?
A:For a grounded system, the connection to the grounding electrode and grounding and bonding must comply with 250.32(B)(1) or (B)(2). Where the feeder is installed underground in rigid metal conduit or other wiring methods listed in 250.118 that provide an adequate grounding path, this equipment grounding conductor is used for grounding and bonding of electrical equipment, structures, etc., in the second building.
Where the feeder conductors are installed overhead as open conductors, an equipment grounding conductor must be provided if there is a continuous metal path (for example, a metal underground water pipe) between the buildings. If this condition exists, the neutral or grounded circuit conductor cannot be connected to the equipment grounding conductor, grounding electrode or grounding electrode conductor.
The equipment grounding conductor must be sized according to Table 250.122. Where there is no continuous metal pipes or metal structures between the two buildings, the system grounded conductor (neutral) cannot be smaller than required by 220.22 or 250.122, whichever results in a larger grounded circuit conductor.
The equipment grounding conductor must also be connected to the grounding electrode at the building served.
Where there are no continuous metallic paths between the two buildings, and there is no ground-fault protection on the service, the grounded circuit conductor in the feeder is connected to the grounding electrode and is used to bond all exposed metal parts of electrical equipment. An equipment grounding conductor is not required to be run with the feeder conductors.
Identification of receptacles in healthcare facilities
Q:Is there a requirement in the National Electrical Code to identify hospital-grade receptacles supplied from the emergency system in a healthcare facility?
A:Yes, there is. The requirement for identification of receptacles connected to the emergency system in healthcare facilities is found in 517.30(E) and reads like this: “Receptacle Identification. The cover plates for the electrical receptacles or the electrical receptacles themselves supplied from the emergency system shall have a distinctive color or marking so as to be readily identifiable.” This sentence is extracted text from NFPA 99-1999 Standard for Health Care Facilities.
In the 1999 edition of the NEC, marking of receptacles by a distinctive color only applied to those connected to the critical branch of the emergency system. Red is the usual color used to identify receptacles connected to these systems; however, there is no color specified for these receptacles.
Q:Are fire sprinkler heads and sprinkler piping allowed in an electrical equipment room that contains nothing but electrical switchgear?
A:Yes, the installation of fire sprinklers and piping are permitted in an electrical equipment room by 110.26(F)(1) and (2). However, the sprinkler pipe and heads cannot encroach on the dedicated space required by these rules. For an indoor installation, the dedicated space is equal to the width and depth of the electrical equipment and extends to a height of 6 feet above or to the structural ceiling if it is less than 6 feet above the electrical equipment. Sprinkler pipes should not enter this zone, but pipes and sprinkler heads in front or in back of the electrical equipment are permitted and should be installed to provide full coverage of the area. This is what the Code says: “Sprinkler protection shall be permitted for the dedicated space where the piping complies with this section.” This information is in 110.26(F)(1)(c).
Disconnect for ranges
Q:Is a disconnecting means that is readily accessible required for an electric range installed in an apartment?
A:If the range is permanently connected to the branch circuit, a disconnecting means must be within sight of the appliance or it must be capable of being locked in the open position if not within sight. A cord-and-plug-connected range does not need a separate disconnecting means where the plug and receptacle are accessible. In fact, the plug and receptacle may serve as the disconnecting means where the receptacle is located in back of the range and is accessible by removal of a drawer in the range. Note that the disconnect does not have to be readily accessible.
In a multifamily dwelling unit (apartment building), if all the range switches have a marked “off” position, they may serve as the disconnecting means provided that another disconnecting means is in the dwelling unit or the same floor on which the range is installed. This disconnecting means may also control other loads.
These options for disconnecting means for appliances are in 422.31 through 422.35.
Taps to grounding electrode conductor
Q:Is it necessary to use irreversible compression-type connectors or exothermic welding where taps are made to the grounding electrode conductor for five fused disconnects that supply tenants in a small strip shopping mall? Each tenant main is supplied through an individual metal raceway and connected to a single service drop.
A:This service arrangement is permitted by 230.40 Exception No. 2 and taps to the grounding electrode conductor are permitted by 250.64(D).
Part (D) of 250.64 does not require irreversible compression type connectors or exothermic welding of the tap conductors to the grounding electrode conductor, but the grounding electrode conductor has to be in one continuous unbroken length. If it is necessary to splice the grounding electrode conductor, irreversible compression type connectors or exothermic welding is required.
This can better be explained by an example. Let’s assume two 200A and three 100A services supply the five shops mentioned in the question. If 3/0 AWG copper conductors are used for each of the 200A services and 2 AWG copper conductors are used for the 100A services, the total circular mil area of the service conductors is (2 x 167,800) + (3 x 66,360) or 534,680 circular mils. According to Table 250.66, a 1/0 AWG copper conductor is required for the grounding electrode conductor that is connected to at least 10 feet of buried metal water pipe or to the effectively grounded metal frame of the building. This 1/0 AWG grounding electrode conductor should be run in an unbroken length from one of the 200A switches to the grounding electrode. From the other 200A switch, a 4 AWG copper grounding electrode conductor is connected to the 1/0 AWG grounding electrode conductor. From each of the 100A switches a 6 AWG copper grounding electrode conductor (if not exposed to physical damage) is run from the switch enclosures to the 1/0 AWG grounding electrode conductor. Listed pressure connectors or listed clamps are acceptable devices for connecting the tap conductors to the grounding electrode conductor.
Notice that the requirements for grounding electrode conductor taps in 250.64(D) are not the same as the requirements for grounding electrode conductor taps in 250.30(A)(3). Where taps are made to ground a separately derived system as outlined in 250.30, they are required to be made with irreversible compression type connectors listed for the purpose, exothermic welding or listed connections to copper bus bars not less than 1/4 inch by 2 inches.
Wiring a pool pump motor
Q:An electrical contractor wired a swimming pool pump motor at a one-family residence with Type NM cable in liquidtight conduit. This wiring extends from a time clock to an outside motor that is exposed to the weather. Is type NM cable acceptable for this installation?
A:No, it is not. Type NM cable is not suitable for this application because 334.10(A) limits its use to dry locations. Also, 350.22(A) does not permit cables in liquidtight flexible metal conduit unless the NM cable article expressly permits NM cable in this conduit. A similar restriction applies to liquidtight flexible nonmetallic conduit in 356.22. However, Item (4) in 680.21 allows the use of NM cable to supply a swimming pool pump motor where located indoors and associated with a one-family dwelling. Where used in this manner, the equipment grounding conductor cannot be smaller than 12 AWG copper.
Grounding parking lot lighting poles
Q:Where an 8-foot ground rod is driven at the base of a metal lighting pole in an automobile parking lot, does the resistance to earth of the ground rod have to be 25 ohms or less?
A:No, it does not. Ground rods are generally specified by the electrical designer to bleed off lightning strokes at or near the metal lighting standard. They are not required by the NEC.
An addition to the 2002 edition of the National Electrical Code covers this subject and bears the title “Supplementary Grounding Electrodes.” It says: “Supplementary grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 and 250.53(C) or the resistance requirements of 250.56, but the earth shall not be used as the sole equipment grounding conductor.”
Since this ground rod is not required by the NEC, the length and diameter of the grounding electrode and grounding electrode conductor size are governed by the plans and specifications. The point of attachment of the grounding electrode conductor to the equipment grounding conductor should also be indicated on the plans. EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.