Article 100—Definitions; Article 210—Branch Circuits; Article 250—Grounding and Bonding; Article 334—Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS; Article 404—Switches; Article 517—Health Care Facilities; Article 680 Swimming Pools, Fountains, and Similar Installations; Article 700—Emergency Systems; Article 702—Legally Required Standby Systems

Use of Type NM cable outdoors

Q: A remote condensing unit that is part of a central cooling system is installed outdoors where it is subject to the weather. Can Type NM-B cable installed in about 6 feet of flexible metal conduit be used to supply this unit? If not, is Type NM-B cable in electrical metallic tubing acceptable?

A: The answer is no to both questions. Part of the definition for Location, Wet reads, “… in unprotected locations exposed to the weather.” Also, 334.10(A)(1) indicates that Type NM cable is permitted in normally dry locations, and 334.12(B)(4) does not allow Type NM cable “Where exposed or subject to excessive moisture or dampness.”

Bonding gas piping

Q: Is the interior gas piping in a one-family residence considered grounded and bonded where a gas-fired central furnace with a blower motor is installed?

A: Yes, the equipment-grounding conductor that is required to be part of the branch circuit to the furnace provides necessary grounding of the gas piping. Interior metal gas piping is required to be bonded to the grounded conductor at the service, to one or more of the grounding electrodes used, or to the equipment-grounding conductor of the branch circuit that may energize the gas piping. The points of attachment of the equipment-grounding conductor (bonding conductor) must be accessible as 250.104(B) requires, and the grounding conductor cannot be smaller than Table 250.122 permits.

Storable swimming pool

Q: A portable swimming pool has a depth measurement of 1 meter (42 inches) to the height of the skimmer, but the pool wall is 1.2 meters (48 inches) from the bottom to the top. Is this a storable pool or a permanent swimming pool?

A: To answer this question, two definitions must be considered. They are Maximum Water Level and Storable Swimming or Wading Pool in Article 680. The definition of maximum water level is “the highest level that water can reach before it spills out.” A storable swimming or wading pool is defined as “those that are constructed on or above the ground and are capable of holding water to a maximum depth of 1.0 m (42 inches), or a pool with nonmetallic, molded polymeric walls or inflatable walls or inflatable fabric walls regardless of dimension.” Unless the pool has the types of walls mentioned in the definition, the water height cannot exceed 42 inches to be considered a storable swimming pool. Therefore, the swimming pool must be wired to comply with Part II Permanently Installed Pools of Article 680 of the National Electrical Code (NEC).

Counting wall space behind open doors

Q: Is it necessary to include the wall space behind open doors when determining the minimum number of receptacles required in a bedroom of a ¬residence?

A: Yes, the measurement for wall space between receptacles begins at the end of the wall. The wall measurement is made assuming the door does not exist. The Code reference for this is 210.52. Part A requires spacing of receptacles in bedrooms to comply with subparts 1 and 2. The requirement in 1 requires a maximum space of 6 feet between receptacles as measured along the floor line, and 2 provides additional information for measuring wall space. Notice that one of the items in 2 requires a receptacle in any space 2 feet or more in width, which includes space measured around corners and unbroken along the floor line at doorways, fireplaces and similar openings.

Frequently, after a residence is furnished and occupied, the receptacle within 2 feet of the door opening is the only one the furniture does not hide and is a convenient location for plugging in the vacuum cleaner or floor polisher.

Size of equipment-grounding conductor

Q: Is it permissible to parallel two sets of 500-kcmil copper conductors in two separate nonmetallic raceways with a single equipment-grounding conductor in one raceway, or must two equipment grounding conductors be used? The voltage is 208Y/120, and overcurrent protection is 800 amperes.

A: An equipment-grounding conductor must be installed in each raceway. Each raceway must contain a 1/0 AWG copper or 3/0 AWG aluminum equipment-grounding conductor.

For conductors in parallel, 250.122(F) requires an equipment-grounding conductor in each raceway, and 250.122(F)(1) requires the equipment-grounding conductor be sized according to Table 250.122. This table requires the equipment-grounding conductor to be based on the ampere rating of the overcurrent device, protecting the parallel feeder conductors.

Emergency standby systems

Q: Does the NEC permit emergency loads, such as exit lighting, and legally required loads, such as communication wiring and smoke removal fans, to be supplied from the same on-site generator and transfer switch?

A: Where the emergency system is installed in a place of assembly to comply with government regulations, Article 700—Emergency Systems applies, and 700.6 limits the transfer switch to emergency loads. Part (D) of 700.6 states, “Use. Transfer equipment shall supply only emergency loads.” Other parts of 700.6 require the identification of transfer switches for emergency use and that transfer switches be electrically operated and mechanically held.

In places of assembly where law requires a standby system, Article 701—Legally Required Standby Systems also applies. The on-site generator must have sufficient capacity to carry the emergency and legally required standby loads simultaneously.

For essential electrical systems in healthcare facilities, the requirements are a little different. Article 517.30 through 517.35 covers them. There are two separate systems: the emergency system and the equipment system. The emergency system is divided into the life safety branch and the critical branch. The number of transfer switches is not limited on the emergency system, and one transfer switch is allowed to supply the life safety branch, the critical branch and the equipment branch in a healthcare facility where the maximum demand on the essential electrical system is 150 kVA or less.

Switch and receptacle in same box

Q: If a 277-volt switch is installed in a two-gang junction box along with a 125-volt, duplex receptacle, must a barrier between these devices be provided if the 125-volt receptacle has push-in terminals with no exposed bare conductors or terminals?

A: Yes, the requirement is in 404.8(B), and it makes no provision for receptacles or switches with no exposed terminals. According to 404.8(B), “Voltage Between Adjacent Devices. A snap switch shall not be grouped or ganged in enclosures with other snap switches, receptacles, or similar devices, unless they are arranged so that the voltage between adjacent devices does not exceed 300 volts, or unless they are installed in enclosures equipped with identified securely installed barriers between adjacent devices.”

Reinforcing steel as grounding electrode

Q: Before adoption of the 2005 edition of the NEC, we were not required to use the reinforcing steel in the foundation of a building. Now we are required to use the reinforcing rods in the building foundation plus one ground rod for a grounding electrode. Is this a correct interpretation of the change in the 2005 Code?

A: Not exactly. Whether there is 10 feet of buried metal water pipe or not, the grounded metal frame of the building must be used. At least 20 feet of reinforcing steel in the concrete foundation must be in direct contact with the earth.

Where not less than 20 feet of one-half (0.5) inch or larger, reinforcing steel is encased in not less than 2 inches of concrete in direct contact with the earth. It must be used as the grounding electrode in addition to buried metal water pipe or building structural steel.

If the reinforcing rods in the concrete slab are the grounding electrode, no other grounding electrode is required. The reinforcing steel is acceptable as the sole grounding electrode for the service.

Outdoor receptacles for multifamily dwellings

Q: Is an outdoor receptacle required for each unit of a multifamily dwelling?

A: Individual receptacles are not required to comply with the NEC. Only apartments located at grade level with individual exterior entrance and egress are required to have outdoor receptacles to comply with 210.52(E). Additional outdoor receptacles must be installed at the site of the remote condensing units to comply with 210.63. However, all of the required receptacle outlets may be supplied from the “house” meter. EC

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.