Code Hunter – Calculations

0
949

To play this game, you need a sharp eye, a quick mind and a 2014 National Electrical Code book.
(Fill-in-the-blank questions are looking for the exact word(s) used in the NEC.)

Questions

1) The sum of the multiconductor cable fill area as a percentage of the allowable fill area for the tray calculated in accordance with 392.22(A), and the single-conductor cable fill area as a percentage of the allowable fill area for the tray calculated in accordance with 392.22(B), totals not more than __________ percent.

A) 50

B) 65

C) 80

D) 100

2) When open-circuit voltage temperature __________ are supplied in the instructions for listed PV modules, they shall be used to calculate the maximum PV system voltage as required by 110.3(B) instead of using Table 690.7.

A) Levels

B) Factors

C) Markings

D) Coefficients

3) Sign and outline lighting outlets shall be calculated at a minimum of __________ volt-amperes for each required branch circuit specified in 600.5(A).

A) 1000

B) 1200

C) 1500

D) 1800

4) For calculated applications, the engineer shall ensure that the downstream circuit breaker(s) that are part of the __________ combination remain passive during the interruption period of the line side fully rated, current-limiting device.

A) Series

B) Listed

C) Tested

D) Certified

5) Branch circuits for lighting and for appliances, including __________ appliances, shall be provided to supply the loads calculated in accordance with 220.10.

A) Heating

B) Fixed-in-place

C) Motor-operated

D) Fastened-in-place

6) Underground service conductors shall have sufficient ampacity to carry the current for the load as calculated in accordance with Article 220 and shall have adequate __________ strength.

A) Tensile

B) Physical

C) Mechanical

D) Elongation

7) The feeder or service neutral load shall be the maximum unbalance of the load determined by this article. The maximum unbalanced load shall be the maximum net calculated load between the __________ conductor and any one ungrounded conductor.

A) Ground

B) Neutral

C) Grounded

D) Grounding

8) For a feeder rated 100 through 400 A, the feeder conductors supplying the entire load associated with a one-family dwelling, or the feeder conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the feeder rating.

A) True

B) False

9) When calculating feeder conductor sizing, show window lighting must be included as a load of not less than 660 volt-amperes/linear meter or 200 volt-amperes/ linear foot, measured horizontally along the base of the show window.

A) True

B) False

10) Conduit fill for single conductors that are twisted together can be calculated based on the overall diameter of the conductor assembly and using the fill percentage for one cable.

A) True

B) False

Bonus Question

[mlw_quizmaster quiz=2]

Answers

1) D, 100. Section 392.80(A)(3) applies to cable trays with a combination of multiconductor and  single-conductor cables. The ampacity of the cables is determined using 392.80(A)(1) for multiconductor cables and 392.80(A)(2) for single-conductor cables, as long as the conditions in 392.80(A)(3)(1) and (2) are met.

2) D, Coefficients. Section 690.7(A), titled “Maximum Photovoltaic System Voltage”, instructs Code users to use Table 690.7 when coefficients are not provided in the manufacturer’s instructions. Table 690.7 provides correction factors for crystalline and multicrystalline silicon modules where the lowest expected ambient temperature is −40°C (−40°F) or higher.

3) B, 1200. This requirement can be found in 220.14(F). For each commercial building and each commercial occupancy accessible to pedestrians, 600.5(A) requires at least one receptacle outlet rated at least 20 amperes for sign or outline lighting system use, and 600.5(B) requires that the load be considered to be continuous for the purposes of calculations.

4) A, Series. In existing installations, licensed professional engineers engaged primarily in the design or maintenance of electrical systems are allowed to select series-rated combination devices that meet the criteria in 240.86(A). This section requires that where a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an acceptable overcurrent protective device having a higher rating, the circuit breaker has to be part of a system selected by the engineer. These systems are typically evaluated using software that compares the opening times for the devices to make sure that they coordinate.

5) C, Motor-operated. This is the opening sentence in 210.11, which goes on to state that: “In addition, branch circuits shall be provided for specific loads not covered by 220.10 where required elsewhere in this Code and for dwelling unit loads as specified in 210.11(C).”

6) C, Mechanical. Section 230.31 requires not only that the conductors have sufficient ampacity, but also that they have sufficient mechanical strength. This ensures that the conductors will be strong enough to survive the force used to pull the conductors without breaking the conductors or reducing the overall diameter of the metal.

7) B, Neutral.  Section 220.61 is used to determine the required size for any service or feeder conductor that is expected to carry neutral load. This conductor size must also be compared to the minimum grounded conductor size required by Table 250.102(C)(1). A new informational note was added in the 2014 NEC that directs the Code user to examples in the Annex: “Informational Note: See Examples D1(a), D1(b), D2(b), D4(a), and D5(a) in Informative Annex D.”

8) A, True. This allowance is found in 310.15(B)(7)(2). For the 2014 NEC, Section 310.15(B)(7) was completely revised to include the ability to use temperature correction and adjustment factors, to allow any suitable wiring method, and to base the conductor size chosen on Table 310.15(B)(16). This section still recognizes the load diversity in residential occupancies by allowing the conductor size to be chosen based on 83% of the rating of the service or feeder overcurrent device.

9) A, True. This language is found in Section 220.43(A). An informational note also directs the user to 220.14(F), where information for sizing branch circuit conductors for show windows is located. While the load calculation for the branch circuit conductors could be based on the unit load, when calculating the feeder or service conductor loads, a minimum of 200 VA/linear foot must be included.

10) B, False. The conduit fill percentage for cables is intended to allow the cable wiring methods in Chapter 3, optical fiber cables, and flexible cords to be considered as a single entity when calculating conduit fill. There is an industry practice of twisting several individual conductors together and placing the assembly on one reel for shipping and installation. However, this practice does not change the essential nature of the product. UL 44 and UL 83 consider these to be “assemblies”; they are specifically differentiated from multiple conductor cables in the UL standards. Since we don’t have a definition for “cable” in the NEC, CMP-8 decided to clarify this issue in Chapter 9, Note 9 for the 2017 NEC with the following language: “Assemblies of single insulated conductors without an overall covering shall not be considered a cable when determining conduit or tubing fill area. The conduit or tubing fill for the assemblies shall be calculated based upon the individual conductors.”