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Quizzes on the Code

Jul 1, 1998 12:00 PM, By Fred Hartwell, Senior Editor

Special Equipment—Articles 604-675, 685-695

Choose the best answer:

1. How much feeder capacity needs to be in place to serve 10 elevator motors with generator field control? Assume one of the motors is 60 hp, and the others are 50 hp (all motors continuous rated) at 460V. Allow 8A for each of the 10 continuous control circuits. Also assume the nameplate current ratings match Table 430-150 values.

1. 590A

2. 747A

3. 761A

4. 767A

5. 781A

2. Suppose each of the elevators in the first question has fused switches in the machine room to serve as a disconnecting means. Which of the following precautions must be applied?

1. Fuses must clear any fault on their load side before the overcurrent device protecting the feeder opens.

2. Switches must be numbered the same as the MG set they control.

3. Switches must have a sign showing the location of the feeder protective device.

4. More than one of the above

5. All of the above

3. Assume the elevator cars have receptacles on the car tops. Which of the following requirements apply?

1. The receptacles must have GFCI protection, however furnished.

2. The receptacles must be only of the GFCI type.

3. Receptacles to be grounded.

4. Both “a” and “c” are true

5. Both “b” and “c” are true

4. Which of the following electric vehicles are covered in the new Art. 625?

1. Golf carts

2. Industrial forklift trucks

3. Airline in-terminal passenger transports

4. None of the above

5. More than one of the above

5. In a high-pollution area, a service station operator on a limited-access toll road decides to gear up for a government mandate for “zero-emission” vehicles, which he assumes to be rechargeable electric vehicles. He decides to build a high-capacity indoor five bay charging facility next to the associated restaurant at the service area. Based on a feeder voltage of 480V, how much ventilation does he need to demonstrate, if the charging circuits are 50A (3-phase) each?

1. 854 cfm

2. 4270 cfm

3. Neither of the above

4. No NEC requirement

6. Which of the following restrictions apply to interior fire pump feeder conductors on the load side of an over-current device?

1. Can’t run in EMT

2. Must run in 2-in. concrete encasement, or under slab

3. Must use a listed electrical circuit protective system

4. Answers “a” and “b”

5. Answers “b” or “c”

6. Answers “a” and “b” or “c”

Answers and Discussion

1. d, Sec. 620-13, 620-14, 620-61(b)(1); 430-24 Ex. 1, Table 430-22(a) Ex. The motors are taken as being used for intermittent duty, and continuous duty motors used for intermittent duty get figured at 140% for all instead of the customary 125% of just the largest motor. Referring to the ampere ratings in Table 430-150, this means taking nine 65A motors and one 77A motor, all at 140%, for a total of 927A. Note that we are actually using the nameplate loads (per Sec. 430-22(a) Ex. 1), because that is the number you should bring into Table 430-22(a) Ex. instead of the customary Table 430-150 values. To this total, Table 620-14 allows a 72% demand factor, which reduces the motor load to 667A. The control circuits are continuous and taken at 125%, or 10A each, for an overall total ampacity requirement of 767A.

2. e, Sec. 620-62, 620-51(d). The selective coordination rule applies because the feeder supplies more than one disconnect, in this case a total of 10. The identification requirements are new in the 1996 NEC.

3. e, Sec. 620-85; 210-7(a). The receptacles need to be grounded and resettable at their location, in order to minimize the necessity for service personnel needing to get off the top of the elevator car to reset a remote protective device.

4. d, Sec. 625-2. Although all of the vehicles listed are electric, none of them are for highway use. Only electric vehicles for highway use come within the new Art. 625, and then only for their charging equipment. The vehicle and all its contained circuitry are beyond the scope of the NEC, as excluded in Sec. 90-2(b)(1).

5. b, Table 625-29(c). The ventilation requirement follows the number of charging bays in addition to the capacity of the charging circuits. Most vehicle battery systems emit hydrogen during the charging process, and it has to be removed in order to prevent hazardous accumulations.

6. f, Sec. 695-8(a-b). EMT is off limits for interior fire pump circuit wiring, and the preferred method of routing the conductors is still based on Art. 230. However, on the load side of an overcurrent device, we don’t need to protect the building from the conductors; we only need to protect the conductors from the building. The electrical circuit protective systems are designed to do exactly that, so either approach is valid.

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