CODE CALCULATIONS Lesson 12

The minimum size neutral conductor permitted for a household wall-mounted oven, electric range, or cooking unit rated 83/4 kW or larger is ? .

10 AWG 210.19(A)(3) Exception No. 2

A 12-unit apartment complex has a 12 kW household range and a 3 kW household oven in each unit. What is the feeder demand for the ranges and ovens in the complex?

12 ranges and 12 ovens Not over 12 kW Table 220.55, Column C 24 (ranges and ovens) = 39 kW

When a household wall-mounted oven is tapped from a 50-ampere branch circuit, the ampacity of the tap conductors shall not be less than ? .

20 A 210.19(A)(3) Exception No. 1

Calculate the following for a single 13.4 kW household range located in a dwelling unit using THWN copper conductors for a 120/240-volt branch circuit. Determine the minimum size THWN copper branch-circuit conductors supplying the range.

210.19(A)(3) Minimum ampacity required is 40 A Table 310.16 for THWN 8 AWG THWN copper has an ampacity of 50 A 10 AWG THWN copper has an ampacity of only 35 A Answer: 8 AWG THWN copper

Calculate the following for a single 13.4 kW household range located in a dwelling unit using THWN copper conductors for a 120/240-volt branch circuit. Determine the minimum size THWN copper grounded (neutral) branch-circuit conductor for the range.

210.19(A)(3) Exception No. 2 Minumum required neutral is 10 AWG THWN Table 310.16 28 A requires a 10 AWG THWN copper with an ampacity of 35 A Neutral Size = 10 AWG THWN copper conductor

Calculate the following for a single 13.4 kW household range located in a dwelling unit using THWN copper conductors for a 120/240-volt branch circuit. Determine the minimum ampacity required for the grounded (neutral) branch-circuit conductor for the range.

210.19(A)(3), Exception No. 2 Neutral conductor: 70% of the branch circuit rating INeutral = Iline × 70% = 40 × 0.70 = 28 A

What are the minimum size Type THWN copper circuit conductors permitted to supply a 6 1/4 kW, 120/240-volt, single-phase, 3-wire electric household dryer installed in a one-family dwelling unit?

220.54 I = kW × 1,000 ÷ E = 6.25 × 1,000 ÷ 240 = 26.04 A 220.5(B) Round to the nearest whole number 26.04 A = 26 A Table 310.16 75°C copper column 35 A for a 10 AWG THWN

Based on single-phase feeders for household range loads rated in volt-amperes for the ungrounded conductors of a single-phase system, identify the Code compliant minimum rating in volt-amperes for the grounded conductor of each feeder. 3,600 VA line-to-line demand 4,500 VA line-to-line demand 17,500 VA line-to-line demand

3,600 VA line-to-line demand → 2,520 VA neutral demand, 4,500 VA line-to-line demand → 3,150 VA neutral demand, 17,500 VA line-to-line demand → 12,250 VA neutral demand

One 10 kW household range is to be installed in each of 36 apartments supplied by a 120/208-volt, 3-phase service. The ranges are equally divided on the three phases. Determine the feeder demand.

36 ranges evenly divided 36 ÷ 3 = 12 ranges on each phase Ranges on adjacent phases 2 × 12 = 24 Table 220.55, Column C 24 ranges = 39 kW or 39,000 VA 39,000 VA = range load on 2 phases Range load on 1 phase = 39,000 ÷ 2 = 19,500 VA 3-phase range load = 19,500 × 3 = 58,500 VA

What is the ungrounded conductor feeder demand for household electric ranges installed in a four-unit multifamily dwelling when the ranges are rated 8.8 kW, 9 kW, 10 kW, and 12 kW?

4 ranges not over 12 kW Table 220.55, Note 2 and Column C 4 ranges = 17 kW Line = 17 kW or 17,000 VA

The minimum branch-circuit rating for a household range rated 83/4 kW shall not be less than ? .

40 A 210.19(A)(3)

An individual branch circuit supplies a household kitchen waste disposer with a motor nameplate rating of 1/2 horsepower, 120 volts, and 5.6 amperes. The disposer is equipped with manual-reset type overload protection. The disposer instructions indicate the electrical installation should follow the NEC. What is the minimum branch circuit conductor size required when using Type NM copper cable to supply the disposer?

422.10(A) Conductors to have an ampacity of not less than the appliance marked rating Nameplate = 5.6 A 334.80, Type NM Cable NM cable not to exceed 60°C ampacity Table 310.16, 60°C copper column 14 AWG has an ampacity of 15 A

What is the minimum required size THHN copper branch-circuit conductors permitted for a single 15 kW, 208-volt, 3-phase electric in-duct heater installed in a bank with a nameplate full-load current of 42 amperes? Assume all equipment is listed at 75°C.

424.4(B), branch-circuit conductors to be sized at 125% of rated load I = rated load × 125% = 42 × 1.25 = 52.5 A Table 310.16 Since all equipment is 75°C, select THHN from the 75°C column 6 AWG THHN = 65 A

The neutral feeder demand for household electric ranges is permitted to be ? of the feeder demand for the ungrounded conductors.

70% 220.61(B)

Based on single-phase feeders for household range loads rated in volt-amperes (VA) for the ungrounded conductors of a single-phase system, identify the Code compliant minimum rating in volt-amperes for the grounded conductor of each feeder. 8,000 VA line-to-line demand 11,000 VA line-to-line demand 12,100 VA line-to-line demand 17,000 VA line-to-line demand

8,000 VA line-to-line demand → 5,600 VA neutral demand, 11,000 VA line-to-line demand → 7,700 VA neutral demand, 12,100 VA line-to-line demand → 8,470 VA neutral demand, 17,000 VA line-to-line demand → 11,900 VA neutral demand

One 10 kW household range is to be installed in each of 36 apartments supplied by a 120/208-volt, 3-phase service. The ranges are equally divided on the three phases. Calculate the minimum required ampacity for the feeder conductors supplying the apartment building. Calculate ampacity to the nearest whole ampere.

I = VA ÷ (E × 1.73) = 58,500 ÷ (208 × 1.73) = 162.57 A

Two 15 kW, 120/240-volt electric commercial ranges are to be installed in a cafe. Calculate the ampacity of the feeder conductors supplying the ranges.

I = VA ÷ E = 30,000 ÷ 240 = 125 A

Calculate the following for a single 13.4 kW household range located in a dwelling unit using THWN copper conductors for a 120/240-volt branch circuit. Determine the minimum required ampacity for the branch-circuit conductors supplying the range.

Section 220.14(B) permits Table 220.55 Note 4 Table 220.55, Note 1 13.4 kW - 12 kW = 1.4 kW Drop 0.4 (not a major fraction, per Note 1) 100% + (1 × 5%) = 105% 1 range using Column C = 8 kW = 8 kW × 1.05 = 8.4 kW → 8,400 VA ILine = VA ÷ E = 8,400 ÷ 240 = 35 A While Table 220.55 calculates the minimum required branch-circuit load at 35 A, 210.19(A)(3) requires a range of 83/4 kW or more to be supplied by a minimum of a 40 A circuit. Also, the circuit conductors are required to have an ampacity of not less than the branch circuit. Answer: 40 A

What is the ungrounded conductor feeder demand for one 10 kW household range installed in a dwelling unit?

Table 220.55, Column C 1 range = 8 kW Line = 8 kW or 8,000 VA

What is the ungrounded conductor feeder demand for two 10 kW household ranges in a dwelling unit?

Table 220.55, Column C 2 ranges = 11 kW Line = 11 kW or 11,000 VA

Calculate the volt-ampere range feeder demand for a 24-unit apartment complex with a 10 kW household range in each apartment when the supply system is 120/240-volt, single-phase.

Table 220.55, Column C 24 ranges at 10 kW each = 39 kW or 39,000 VA

A 30-unit apartment complex has a 10 kW household range in each apartment. What is the feeder demand for the ranges?

Table 220.55, Column C 30 ranges = 15 kW + 1 kW per range 30 ranges × 1 kW = 30 kW Line = 15 kW + 30 kW = 45 kW → 45,000 VA

An apartment complex has a 12 kW range in each of its 44 apartments. What is the feeder demand for the household ranges?

Table 220.55, Column C 44 ranges at 25 kW + 3/4 kW per range 44 ranges × 3/4 kW = 33 kW Line = 33 kW + 25 kW = 58 kW → 58,000 VA

What is the ungrounded conductor feeder demand for two 14 kW household electric ranges installed in a dwelling unit?

Table 220.55, Note 1 14 kW exceeds 12 kW by 2 Increase 5% per kW over 12 100% + (2 × 5%) = 110% Table 220.55, Column C 2 ranges = 11 kW Line = 11 kW × 1.10 = 12.1 kW or 12,100 VA

One 10 kW range, one 15 kW range, and one 24 kW range are to be installed in a multifamily dwelling. What is the feeder demand for the three household ranges for the ungrounded conductors only?

Table 220.55, Note 2 Over 83/4 kW, Unequal ratings Average ratings using 12 kW for any range less than 12 kW Use 12 kW (for 10 kW range) Total Loads = 12 + 15 + 24 = 51 kW Average load = 51 ÷ 3 = 17 kW 17 kW exceeds 12 kW by 5 kW 100% + (5 × 5%) = 125% Table 220.55, Column C 3 ranges = 14 kW Line = 14 kW × 1.25 = 17.5 kW → 17,500 VA

What is the minimum ungrounded conductor(s) feeder demand for two 3 kW household electric ovens in a dwelling unit?

Table 220.55, Note 3 permits two options. Calculate both options and select the smaller. Option 1 Table 220.55, Column A Two units less than 31/2 kW 2 units = 75% Line = 2 units × 3 kW × 0.75 = 4.5 kW Option 2 Table 220.55, Column C 2 units = 11 kW Selection: Option 1 gives smaller load Answer: 4.5 kW

What is the branch-circuit demand load for a 2 1/2 kW household cooktop and a 2 kW household oven for a dwelling unit (based on the ungrounded conductors of a single-phase, 3-wire feeder)?

Table 220.55, Note 4 Add loads and treat as one 2.5 + 2 = 4.5 kW Use Column B 1 range Column B = 80% Line = 4.5 kW × 0.80 = 3.6 kW or 3,600 VA

Five 10 kW electric household ranges are to be installed in the culinary arts lab in a high school for instruction cooking classes. What is the feeder demand for the ranges?

Table 220.55, Note 5, Column C 5 ranges = 20 kW Line = 20 kW or 20,000 VA

Two 15 kW, 120/240-volt electric commercial ranges are to be installed in a cafe. Determine the feeder demand supplying the ranges.

Table 220.56 2 units = 100% demand factor = 2 × 15 kW = 30 kW → 30,000 VA

What is the feeder demand for three 12 kW commercial ranges, one 150-gallon 25 kW water heater, one 2,500-watt booster heater, and three 2,000-watt warming ovens to be installed in a restaurant?

Table 220.56 3 ranges at 12 kW = 36.0 kW 1 water heater = 25.0 kW 1 booster heater = 2.5 kW 3 ovens at 2 kW = 6.0 kW Total for 8 units = 69.5 kW Over 6 units, 65% demand factor 69.5 × 0.65 = 45.175 kW → 45,175 VA

What is the minimum size Type NM nonmetallic sheathed cable using copper branch-circuit conductors to supply a 50-gallon storage-type water heater? The water heater is rated 240 volts AC, single-phase. It has two non-simultaneously operated upper and lower heating elements rated 4,250-watts.

Use Type NM cable for branch circuit I = W ÷ E = 4,250 ÷ 240 = 17.71 A Section 422.13, branch-circuit conductors to be sized at 125% of rated load I = rated load × 125% = 17.71 × 1.25 = 22.13 A → 22 A Section 334.80 NM cable ampacity selected for 60°C rated conductors Table 310.16, 60°C copper column 10 AWG has an ampacity of 30 A 10 AWG = 10-2 NM Cable