NEC Questions and Answers – Based on the 2011 NEC

February 2012

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. Does the NEC require sizing conduit and conduit support racks large enough for future expansion?

A1. No. The Code contains requirements considered necessary for a safe electrical installation. If an electrical installation is installed in compliance with the, it will be essentially free from electrical hazards. The Code is a safety standard, not a design guide [90.1(B)].

NEC requirements aren’t intended to ensure the electrical installation will be efficient, convenient, adequate for good service, or suitable for future expansion. Specific items of concern, such as electrical energy management, maintenance, and power quality issues aren’t within the scope of the Code.

The NEC doesn’t require electrical systems to be designed or installed to accommodate future loads. However, the electrical designer, typically an electrical engineer, is concerned with not only ensuring electrical safety (Code compliance), but also with ensuring the system meets the customers’ needs, both of today and in the near future. To satisfy customers’ needs, electrical systems are often designed and installed above the minimum requirements contained in the NEC. But just remember, if you are taking an exam, licensing exams are based on your understanding of the minimum Code requirements.

Q2. What is the Code requirement for the emergency shutoff for spas and hot tubs?

A2. In other than a single-family dwelling, a clearly labeled emergency spa or hot tub water recirculation and jet system shutoff must be supplied. The emergency shutoff must be readily accessible to the users and located not less than 5 ft away, but adjacent to and within sight of the spa or hot tub [680.41].

•    Either the maintenance disconnecting means required by 680.12 or a pushbutton that controls a relay located in accordance with this section can be used to meet the emergency shutoff requirement.

•    The purpose of the emergency shutoff is to protect users. Deaths and injuries have occurred in less than 3 ft of water because individuals became stuck to the water intake opening. This requirement applies to spas and hot tubs installed indoors as well as outdoors.

Q3. What is the Code requirement for a maintenance disconnect for a spa or hot tub?

A3. A maintenance disconnecting means is required for a permanently installed pool, storable pool, outdoor spa, outdoor hot tub, or fountain equipment, other than lighting for these water bodies.

The maintenance disconnecting means must be readily accessible and located within sight and at least 5 ft from the permanently installed pool, storable pool, outdoor spa, outdoor hot tub, or fountain equipment unless separated from the open water by a permanently installed barrier that provides a 5 ft reach path or greater. This horizontal distance is measured from the water’s edge along the shortest path required to reach the disconnecting means [680.12].

Q4. What size overcurrent protection is required on 14 AWG used for general branch circuit wiring? 

A4. 15A. Unless specifically permitted in 240.4(E) or (G), overcurrent protection must not exceed the following [240.4(D)]:

(1)     18 AWG Copper—7A

(2) 16 AWG Copper—10A

(3) 14 AWG Copper—15A

(4) 12 AWG Aluminum/Copper-Clad Aluminum—15A

(5) 12 AWG Copper—20A

(6) 10 AWG Aluminum/Copper-Clad Aluminum—25A

(7) 10 AWG Copper—30A

Q5. What is the GFCI requirement for a receptacle behind a refrigerator in a dwelling family room that is located within 6 ft from the edge of a wet bar sink?

A5. GFCI protect is required for all 15A and 20A, 125V receptacles located within an arc measurement of 6 ft from the outside edge of the sink not located in a kitchen [210.8(A)(7)].

If the sink was in the dwelling unit kitchen, then GFCI protection would NOT be required [210.8(A)(6)].

Q6. Can a ground rod alone be used to ground a light pole or other equipment instead of installing an equipment grounding conductor?

A6. No. A ground rod to a light pole or other equipment is considered an auxiliary electrode by the Code and can’t take the place of an equipment grounding conductor.

Auxiliary electrodes can be connected to the circuit equipment grounding conductor. They’re not required to be bonded to the building or structure grounding electrode system, the grounding conductor to the electrode isn’t required to be sized to 250.66, and their contact resistance to the earth isn’t required to comply with the 25 ohm requirement of 250.53(A)(2) Ex [250.54].

Caution: An auxiliary electrode typically serves no useful purpose, and in some cases it may actually cause equipment failures by providing a path for lightning to travel through electronic equipment.

The earth must not be used as the effective ground-fault current path required by 250.4(A)(5).

DANGER: Because the contact resistance of an electrode to the earth is so great, 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.

Q7. What is the minimum wire bending space requirement for conductors that enter a panel from a metal wireway?

A7. If conductors are bent within a metal wireway, the wireway must be sized to meet the bending radius requirements contained in Table 312.6(A), based on one wire per terminal [376.23(A)].

Q8. Is there a minimum depth required for a junction box when conductors enter from the back of the box?

A8. Yes. When insulated conductors 4 AWG or larger enter an enclosure in the wall opposite a removable cover,  the distance from where the conductors enter to the removable cover must not be less than the bending distance as listed in Table 312.6(A) for one conductor per terminal [314.28(A)(2) Ex].

Q9. What does the Code mean when it refers to a multiwire branch circuit?

A9. A multiwire branch circuit is a branch circuit that consists of two or more ungrounded circuit conductors with a common neutral conductor. There must be a difference of potential (voltage) between the ungrounded conductors and an equal difference of potential (voltage) from each ungrounded conductor to the common neutral conductor [Article 100 Definition, Branch Circuit, Multiwire].

Author’s Comment: Multiwire branch circuits offer the advantage of fewer conductors in a raceway, smaller raceway sizing, and a reduction of material and labor costs. In addition, multiwire branch circuits can reduce circuit voltage drop by as much as 50 percent. However, because of the dangers associated with multiwire branch circuits, the NEC contains additional requirements to ensure a safe installation. See 210.4, 300.13(B), and 408.41 for details.

Q10. What is the Code rule for disconnecting multiwire branch circuits?

A10. Each multiwire branch circuit must have a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates [210.4(B)].

Note: Individual single-pole circuit breakers with handle ties identified for the purpose, or a breaker with a common internal trip, can be used for this application, see 240.15(B)(1).

Caution: This rule is intended to prevent people from working on energized circuits they thought were disconnected.

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