NEC Questions and Answers – Based on the 2011 NEC
October 2011 - Part 1 of 2

By Mike Holt for EC&M Magazine

Here’s the follow up to yesterday’s newsletter. This includes all of the answers to the questions sent, so you can see how you did.

 

Q1. When adding a ceiling outlet for a new paddle fan in a bedroom, does the Code require this circuit addition to be AFCI protected?

A1. Where branch-circuit wiring is modified, replaced, or extended in any of the areas of a dwelling unit specified in 210.12(A), the branch circuit must be protected by [210.12(B)]:

• A listed combination AFCI located at the origin of the branch circuit; or
• A listed outlet branch circuit AFCI located at the first receptacle outlet of the existing branch circuit.

 

Q2. Section 220.54 expresses dryer loads in watts and Table 220.55 provides wattage demands for ranges. Can watts be converted to VA for service calculations?

A2. Yes. The feeder/service load for electric clothes dryers located in a dwelling unit must not be less than 5,000W (5,000 VA), or the nameplate rating of the equipment if more than 5,000W (5,000 VA). Kilovolt-amperes (kVA) is considered equivalent to kilowatts (kW) for loads calculated in this section [220.54].

When a building contains five or more dryers, it’s permissible to apply the demand factors listed in Table 220.54 to the total connected dryer load.

Author’s Comment: A clothes dryer load isn’t required if the dwelling unit doesn’t have an electric clothes dryer circuit receptacle outlet.

 

Q3. In what rooms of a dwelling unit are switched receptacles allowed to be used for the required lighting outlets?

A3. At least one wall switch-controlled lighting outlet must be installed in every habitable room and bathroom of a dwelling unit [210.70(A)(1)].

Author’s Comment: See the definition of “Lighting Outlet” in Article 100.

Ex 1: In other than kitchens and bathrooms, a receptacle controlled by a wall switch can be used instead of a lighting outlet.

Ex 2: Lighting outlets can be controlled by occupancy sensors equipped with a manual override that permits the sensor to function as a wall switch.

Author’s Comment: The Code specifies the location of the wall switch-controlled lighting outlet, but it doesn’t specify the switch location. Naturally, you wouldn’t want to install a switch behind a door or other inconvenient location, but the NEC doesn’t require you to relocate the switch to suit the swing of the door. When in doubt as to the best location to place a light switch, consult the job plans or ask the customer.

Q4. Does the NEC require that conductors be twisted together before a twist-on wire connector is installed?
A4.  Conductors must be spliced by a splicing device identified for the purpose or by exothermic welding [110.14(B)].

Author’s Comment: Conductors aren’t required to be twisted together prior to the installation of a twist-on wire connector, unless specifically required in the installation instructions.


Q5. Are there any requirements for the terminals used for the connection of aluminum conductors?
A5. Conductor terminal and splicing devices must be identified for the conductor material and they must be properly installed and used [110.14].

Connectors and terminals for conductors more finely stranded than Class B and Class C, as shown in Table 10 of Chapter 9, must be identified for the conductor class.

Author’s Comment: According to UL Standard 486 A-B, a terminal/lug/connector must be listed and marked for use with conductors stranded in other than Class B. With no marking or factory literature/instructions to the contrary, terminals may only be used with Class B stranded conductors.

Switches and receptacles marked CO/ALR are designed to ensure a good connection through the use of the larger contact area and compatible materials. The terminal screws are plated with the element called “Indium.” Indium is an extremely soft metal that forms a gas-sealed connection with the aluminum conductor.

Author’s Comments:

•  See the definition of “Identified” in Article 100.

•  Conductor terminations must comply with the manufacturer’s instructions as required by 110.3(B). For example, if the instructions for the device state “Suitable for 18-12 AWG Stranded,” then only stranded conductors can be used with the terminating device. If the instructions state “Suitable for 18-12 AWG Solid,” then only solid conductors are permitted, and if the instructions state “Suitable for 18-12 AWG,” then either solid or stranded conductors can be used with the terminating device.

Copper and Aluminum Mixed. Copper and aluminum conductors must not make contact with each other in a device unless the device is listed and identified for this purpose.

Author’s Comment: Few terminations are listed for the mixing of aluminum and copper conductors, but if they are, that will be marked on the product package or terminal device. The reason copper and aluminum shouldn’t be in contact with each other is because corrosion develops between the two different metals due to galvanic action, resulting in increased contact resistance at the splicing device. This increased resistance can cause the splice to overheat and cause a fire.

Note: Many terminations and equipment are marked with a tightening torque, see Table I.1 in Informative Annex I.

Author’s Comment: Conductors must terminate in devices that have been properly tightened in accordance with the manufacturer’s torque specifications included with equipment instructions. Failure to torque terminals can result in excessive heating of terminals or splicing devices due to a loose connection. A loose connection can also lead to arcing which increases the heating effect and also may lead to a short circuit or ground fault. Any of these can result in a fire or other failure, including an arc-flash event. In addition, this is a violation of 110.3(B), which requires all equipment to be installed in accordance with listing or labeling instructions.

Question: What do you do if the torque value isn’t provided with the device?

Answer: Call the manufacturer, visit the manufacturer’s Website, or have the supplier make a copy of the installation instructions.

Author’s Comment: Terminating conductors without a torque tool can result in an improper and unsafe installation. If a torque screwdriver isn’t used, there’s a good chance the conductors aren’t properly terminated.

 

Q6. What are the Code requirements for a concrete encased electrode?

A6. A concrete-encased electrode must consist of at least 20 ft of either of the following [250.52(A)(3)]:

(1) One or more of bare, zinc-galvanized, or otherwise electrically conductive steel reinforcing bars of not less than ½ in. diameter, mechanically connected together by steel tie wires, welding, or other effective means, to create a 20 ft or greater length.

(2) Bare copper conductor not smaller than 4 AWG.

The reinforcing bars or bare copper conductor must be encased by at least 2 in. of concrete located horizontally near the bottom of a concrete footing or vertically within a concrete foundation that’s in direct contact with the earth.

If multiple concrete-encased electrodes are present at a building/structure, only one is required to serve as a grounding electrode.

Note: Concrete containing insulation, vapor barriers, films or similar items separating it from the earth isn’t considered to be in “direct contact” with the earth.

Author’s Comments:

•  The grounding electrode conductor to a concrete-encased grounding electrode isn’t required to be larger than 4 AWG copper [250.66(B)].

•  The concrete-encased grounding electrode is also called a “Ufer Ground,” named after a consultant working for the U.S. Army during World War II. The technique Mr. Ufer came up with was necessary because the site needing grounding had no underground water table and little rainfall. The desert site was a series of bomb storage vaults in the area of Flagstaff, Arizona. This type of grounding electrode generally offers the lowest ground resistance for the cost.

 

Q7.  Is an over-counter light in a dwelling unit kitchen allowed to be hardwired to the small-appliance circuit?

A7. Not Supply Other Outlets. The 20A, 120V small-appliance circuits required by 210.11(C)(1) must not supply outlets for luminaires or appliances [210.52(B)(2)].

Ex 1: The 20A, 120V small-appliance branch circuit can be used to supply a receptacle for an electric clock.

Ex 2: A receptacle can be connected to the small-appliance branch circuit to supply a gas-fired range, oven, or counter-mounted cooking unit.

Author’s Comment: A range hood or above the range microwave listed as a range hood must be supplied by an individual branch circuit [422.16(B)(4)(5)].

 

Q8. If you replace a two-wire receptacle with no equipment grounding conductor with a GFCI, is an equipment grounding conductor required for the GFCI?

A8. If no equipment grounding conductor exists in the outlet box for the receptacle, such as old 2-wire Type NM cable without an equipment grounding conductor, existing nongrounding-type receptacles can be replaced using one of the following [406.4(D)(2)]:

(a)   Another nongrounding-type receptacle.

(b)   A GFCI-type receptacle marked “No Equipment Ground.”

(c)   A grounding-type receptacle, if GFCI protected and marked “GFCI Protected” and “No Equipment Ground.”

Author’s Comment: GFCI protection functions properly on a 2-wire circuit without an equipment grounding conductor because the circuit equipment grounding conductor serves no role in the operation of the GFCI-protection device. See the definition of “Ground-Fault Circuit Interrupter” for more information.

Caution: The permission to replace nongrounding-type receptacles with GFCI-protected grounding-type receptacles doesn’t apply to new receptacle outlets that extend from an existing outlet box that’s not connected to an equipment grounding conductor. Once you add a receptacle outlet (branch-circuit extension), the receptacle must be of the grounding type and it must have its grounding terminal connected to an equipment grounding conductor of a type recognized in 250.118, in accordance with 250.130(C).

 

Q9. What is the purpose of grounding electrical systems?

A9. Electrical power systems, such as the secondary winding of a transformer are grounded (connected to the earth) to limit the voltage induced by lightning, line surges, or unintentional contact by higher-voltage lines [250.4(A)(1)].

Author’s Comment: System grounding helps reduce fires in buildings as well as voltage stress on electrical insulation, thereby ensuring longer insulation life for motors, transformers, and other system components.

Note: An important consideration for limiting imposed voltage is to remember that grounding electrode conductors shouldn’t be any longer than necessary and unnecessary bends and loops should be avoided.

 

 

Q10. What is the purpose of grounding electrical equipment?

A10. Metal parts of electrical equipment are grounded (connected to the earth) to reduce induced voltage on metal parts from exterior lightning so as to prevent fires from an arc within the building/structure [250.4(A)(2)].

DANGER: Failure to ground the metal parts can result in high voltage on metal parts from an indirect lightning strike to seek a path to the earth within the building—possibly resulting in a fire and/or electric shock.

Author’s Comment: Grounding metal parts helps drain off static electricity charges before flashover potential is reached. Static grounding is often used in areas where the discharge (arcing) of the voltage buildup (static) can cause dangerous or undesirable conditions [500.4 Note 3].

Danger: Because the contact resistance of an electrode to the earth is so high, very little fault current returns to the power supply if the earth is the only fault current return path. Result—the circuit overcurrent device won’t open and clear the ground fault, and all metal parts associated with the electrical installation, metal piping, and structural building steel will become and remain energized.

 

 

 

 

For more NEC Practice purchase Mike Holt's NEC Practice Questions book, Based on the 2011 NEC. www.MikeHolt.com/NEC