Article 200—Use and Indentification of Grounded Conductors;
Article 225—Outside Branch Circuits and Feeders;
Article 410—Lighting Fixtures, Lampholders, Lamps, and Receptacles;
Article 517—Health Care Facilities.
The General Information for Electrical Equipment Directory and Fire Resistance Directory, both published by Underwriters Laboratories, Inc., are also mentioned.
Service and feeder to a building
Q:Does the National Electrical Code (NEC) permit a service and feeder to the same building?
A:The answer is “yes.” Section 225-30 permits a single feeder or branch circuit to be run from one building to another where the building is on the same property and under single management. Other conditions in Section 225-30 allow more than one feeder or branch circuit to a building, such as emergency systems, fire pumps, different voltages, frequencies, phases, etc.
Section 230-2 limits the number of services to a building to one, but similar conditions to those in Section 225-30 exist that allow additional services. In fact, the conditions that allow more than one feeder or service to a building are the same except for the words “feeders and branch circuits” in Section 225-30 and the word “services” in Section 230-2. Because these two Sections are not dependent on each other, a single feeder and a service are permitted on the same building without considering any of the special conditions, special occupancies, capacity requirements, or different characteristics outlined in parts (a) through (d) of Sections 225-30 and 230-2.
A plaque or directory must be provided at the service equipment to indicate where the feeder disconnecting means is located. Also, a sign must be located at the feeder disconnect to indicate the location of the service disconnecting means. These requirements are found in Sections 225-37 and 230-2(e).
Bonding conductor size for metal gas pipe
Q:Section 250-104(b) of the 1999 NEC requires that the interior metal gas pipe be bonded to the grounding electrode system. Should the size of this bonding conductor be based on Table 250-66 or Table 250-122?
A: Notice that this part (b) has a superscript, meaning the text is extracted from another National Fire Protection Association (NFPA) Standard. In this instance, the extract is from paragraph 3.14(a) of the National Fuel Gas Code, NFPA 54-1996. As sometimes happens, the extracted material does not provide sufficient guidance to comply with the requirement. This is the way the rule reads: “Each above ground portion of a gas piping system upstream from the equipment shut off valve shall be electrically continuous and bonded to the grounding electrode system.”
This leaves us with two choices: Use either Table 250-66 or Table 250-122. Since the gas piping is not recognized or permitted as a grounding electrode (See 250-52(a)), it is safe to assume that a conductor size based on Table 250-122 is intended. This table allows the grounding conductor to be sized based on the ampere rating of the overcurrent device supplying the circuit that could energize the metal gas piping.
The basis for this answer is found in Section 250-104(c) which covers “other metal piping.” In this part (c) this sentence appears: “The bonding jumper shall be sized in accordance with Table 250-122 using the rating of the circuit that may energize the piping.” For example, a gas furnace with a one horsepower, 240-volt, single-phase blower motor protected at 20 amperes would require a No. 12 copper bonding jumper from the motor frame to the gas piping if the motor frame is not bonded to the furnace and gas piping.
Cold cathode lighting in a dwelling
Q: Does the 1999 NEC permit the installation of cold cathode lighting fixtures in a cove that is high on all walls of a den in a one-family dwelling? If the answer is “yes,” what is the maximum voltage permitted at the fixture sockets?
A:The answer is “yes.” Cold cathode fixtures may be installed in a residence if the design of the fixtures meets the requirements outlined in Section 410-75. Here are the requirements: “Open-Circuit Voltage Exceeding 300 Volts. Equipment having an open-circuit voltage exceeding 300 volts shall not be installed in dwelling occupancies unless such equipment is designed so that there will be no exposed live parts when lamps are being inserted, are in place, or are being removed.” These are logical requirements, but how do the installing electrician and electrical inspector know the fixture is designed to meet these requirements? First, read all of the information in the fixture catalog to make sure that there will be no exposed live parts during lamp replacement and while the lamp is in place. Also, the General Information for Electrical Equipment Directory published by Underwriters Laboratories Inc. provides additional guidance. Here is some information that appears in the directory under the category, Electric Discharge Lighting Systems, Cold Cathode (IFAY). “The listing of a lighting system does not constitute approval of the design which is the responsibility of the manufacturer and the Authority Having Jurisdiction nor approval of the installation. The final acceptance of the field-installed lighting system is the responsibility of the Authority Having Jurisdiction.”
“These lighting systems may incorporate transformers, power supplies, or ballasts that have a marked output voltage greater than 1,000 volts. Such systems are not intended for use in dwellings in accordance with Article 410 of the National Electrical Code.”
“These lighting systems may incorporate ballasts that have marked output voltages 1,000 volts or less. Such systems are intended for use in dwellings and other premises when provided with circuit interrupting lamp holders that de-energize the circuit during lamp replacement, unless they are marked ‘Not for dwelling use.’”
Notice that although the system is listed, it is the electrical inspector’s responsibility to accept or reject the installation. Also, look for any markings that indicate the fixture is not suitable for installation in a dwelling.
Receptacles connected to isolated power systems
Q:We are installing a 10 kVA, 480-volt, single-phase isolating transformer in a hospital. The secondary voltage is 120. There will be some 15- and 20-ampere, 125-volt receptacles supplied from this transformer. Since the circuits are ungrounded, are special receptacles required? That is, are there any 125-volt receptacles without identified (white) terminals that are required for this job?
A: The answer to both questions is “no.” Special terminal markings are not required on the receptacles. Section 200-10(b) provides guidance for manufacturers of receptacles. This part (b) indicates that the terminal on the receptacle that is intended for connection to the grounded circuit conductor be substantially white in color or marked “white” or with the letter “W” adjacent to the identified terminal.
Part (a)(5) of Section 517-160 requires that the isolated circuit conductors be color coded. One conductor is orange and the other is brown. In this part, there is a requirement that the orange conductor be connected to the white terminal on the receptacle.
Penetration of cables in fire-rated construction
Q: Have any armored cables (Type AC) or metal-clad cables (Type MC) been tested for penetration of fire rated walls, floors, or ceilings?
A: Yes, some cable manufacturers have submitted their products to Underwriters Laboratories Inc. for evaluation and have obtained classification by UL for through-penetration firestopping.
Some of the products that are classified for through-penetration firestopping include Types AC and MC cables that may have steel or aluminum armor and may contain copper or aluminum conductors. Wire sizes vary from No. 12 through 750 kcmil.
Here is an example of the information in Volume 2 of the Fire Resistance Directory, published by Underwriters Laboratories Inc.: For this through-penetration firestop system the floor or wall being penetrated must be at least 41/2 inches thick. Lightweight or normal weight concrete or classified concrete block must be used for the construction. The maximum diameter of the opening is limited to 6 inches. This hole must be 3/4 to 11/2 inches in diameter larger than the cable diameter. Maximum of four copper conductors No. 2/0 or smaller MC cable with steel or aluminum armor, or Type AC with steel or aluminum armor are permitted.
The void space around the cable must be packed with polyethylene backer rod or nominal 1-inch thickness of mineral wool insulation firmly packed into the opening. This packing material must be recessed from the top surface of the floor or from both surfaces of the wall to accept the required thickness of caulk fill material. Caulk is applied to fill the annular space around the cable penetration. Where the hole is not larger than 3 inches in diameter, the caulk thickness does not have to be greater than 1/2 inch. Where the opening is larger than 3 inches, the caulk thickness has to be at least 1 inch. The caulk must be installed flush with the floor. For walls the caulk must be flush with the wall surface on both sides.
Cables must be rigidly supported on both sides of the floor or wall. The names of the cable and caulking compound manufacturers, plus the latter’s catalog number, are also included as part of the through-penetration firestop system.
As you can see from this short discussion, requirements are very specific and detailed. Since there are more than 50 different through-penetration firestop systems for armored and metal-clad cable in the 1999 directory, you should review all of them and pick one that is not too expensive nor too time consuming to apply, and satisfies your needs.
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.