Elect Code Calc Lvl II - 2023 NEC Lesson 5: Calculating the Parameters of Multifamily Dwelling Loads in Accordance with the NEC

Determine the smallest size THWN copper service conductor permitted for the ungrounded service conductors for a multifamily dwelling service. The calculated load for the building is 70,500 VA using a 120/240-volt, single-phase, 3-wire utility supply.

350kcmil

A multifamily dwelling has eight 1,350-square-foot units, each served with a 120/240-volt THWN copper conductor feeder, with the following in each unit: • 3.5kW, 240V water heater • 12kW, 120/240V range • 1,750W, 120V dishwasher • 4kW, 120/240V dryer • 120V, 1/3hp garbage disposal • 7 1/2hp, 240V air-conditioning unit Calculate the feeder demand load for each unit. Round the answer to the nearest whole number

36057

Determine the smallest standard size service permitted for a multifamily dwelling with a load of 95,000 volt-amperes for the line using a 120/240-volt, single-phase, 3-wire utility supply.

400A

What is the ampacity of the grounded (or neutral) feeder conductors with a calculated load of 169 kVA, when the service is 120/240-volt, single-phase, 3-wire? Round the answer to the nearest whole number.

553 A

Using the total ampere load shown for each feeder, determine the appropriate THWN copper wire size based upon three parallel conductors per phase.

558 A → 3/0 AWG, 758 A → 250 kcmil, 858 A → 350 kcmil, 958 A → 400 kcmil

The feeder demand for a multifamily dwelling is calculated to be 345,000 volt-amperes for the line. When the service is 3-phase, 120/208-volt, 4-wire, and the lighting is incandescent, calculate the total ampacity of the line conductors. Round the answer to the nearest whole number.

A = VA ÷ (E × 1.73) = 345,000 ÷ (208 × 1.73) = 345,000 ÷ 359.84 = 958.76 A → 959 A The correct answer is: 959 A

A 16-unit multifamily dwelling has two fixed 120-volt appliances installed in each of its 16 units. The two appliances installed in each unit are one 1.3-kilowatt dishwasher and one 5.5-ampere disposal. What is the feeder demand, in volt-amperes, for the line (and neutral) for the appliances for the apartment complex? Round the answer to the nearest whole number.

Dishwashers: 16 units × 1,300 VA = 20,800 VA Disposals: VA = E × I × 16 units = 120 × 5.5 × 16 = 10,560 VA Total fixed appliance 31,360 VA 220.53, 75% demand applies Demand load = VA × demand factor = 31,360 × 0.75 = 23,520 VA The correct answer is: 23520

Calculate the number of 20-ampere lighting branch circuits required in each unit. Round the answer to the nearest whole number.

I = VA ÷ E = 6,000 VA ÷ 120 V = 50 A Number of circuits = I ÷ circuit size = 50 ÷ 20= 2.5 or 3 The correct answer is: 3

The feeder demand for a multifamily dwelling is calculated to be 256,000 volt-amperes. When the service is 3-phase, 120/208-volt, 4-wire, and the lighting is incandescent, calculate the total ampacity of the neutral conductor. Round the answer to the nearest whole number.

Note: See NEC 220.61(B)(2). A = VA ÷ (E × 1.73) = 256,000 ÷ (208 × 1.73) = 256,000 ÷ 359.84 = 711.43 A Total current = 711.43 First 200 at 100% - 200.00 200 Balance at 70% 511.43 × 70% = + 358 Neutral ampacity = 558 A The correct answer is: 558 A

A 36-unit apartment has a 13-kilowatt, 120/240-volt range in each unit. What is the range feeder demand for the ungrounded conductor load for the complex? Round the answer to the nearest whole number.

Step 1 Table 220.55 Column C 36 ranges = 15 kW + 1 kW for each additional range = 15 kW + 36 kW= 51 kW Step 2 Adjust for over 12 kW; use Table 220.55, Note1 13 kW range exceeds 12 by 1 Increase value of Column C by 5% (105%) Line load = 51 kW × 105% = 53.55 kW → 53,550 VA The correct answer is: 53550

A quadruplex multifamily dwelling has a five-kilowatt, 240-volt dryer installed in each unit. Calculate the feeder demand in volt-amperes for the dryers. Round the answer to the nearest whole number.

Table 220.54 4 dryers = 100% Demand factor Line load = Number of dryers × rating × demand factor = 4 × 5 × 1.00 = 20 kW → 20,000 VA The correct answer is: 20000

Calculate the service demand load for the neutral for the entire dwelling. The service is 120/240-volt, single-phase. Round the answer to the nearest whole number of volt-amperes (VA).

122801 VA

What is the ampacity of the ungrounded feeder conductors with a calculated 312 kVA load, when the service is 120/240-volt, single-phase, 3-wire? Round the answer to the nearest whole number.

1300A

Each unit of a 12-unit multifamily dwelling is 2,000 square feet and supplied by a 120/240-volt, 3-wire system. Calculate the lighting load for each unit. Round the answer to the nearest whole number

220.41 Unit load for dwelling units = 3 VA per ft.2 Calc. load = area × unit load = 2,000 × 3= 6,000 VA The correct answer is: 6000 VA

A multifamily complex has 30 units with a 120/240-volt, six-kilowatt dryer in each unit. What is the dryer load feeder demand for the ungrounded (or line) conductors of this complex? Round the answer to the nearest whole number.

220.54 Over 5 kW, use nameplate rating Load = number of dryers × 6 kW = 30 × 6 = 180 kW → 180,000 VA Table 220.54, Demand factor (DF) For 30 dryers% DF = 35 - [0.5 × (number of dryers - 23)] = 35 - [0.5 × (30 - 23)] = 35 - [0.5 × 7]= 35 - 3.5 = 31.5% Demand = load × demand factor = 180,000 VA × 0.315 = 56,700 VA The correct answer is: 56700

According to Article 220, Part III, the total dryer load on a service (or feeder) neutral load of a multifamily occupancy may be calculated at ? of the ungrounded conductor volt-ampere load.

220.61(B)(1) The correct answer is: 70%

Determine the minimum size copper grounding electrode conductor (GEC) using the metal in-ground support structure as the grounding electrode for a 3-phase, 4-wire, 480/277-volt service using three parallel 400 kcmil THWN copper service conductors per phase and neutral.

3/0

An 18-unit multifamily dwelling, with each dwelling a self-contained unit, has the following equipment installed in each 1,200-square-foot apartment. The only thing common to the complex is the security lighting, consisting of eight motion-activated (non-continuous) 100-watt, 120-volt LED lighting standards. Security lighting is non-continuous. • 5kW, 120/240V dryer • 3kW, 240V water heater • 5hp, 240V air-conditioning unit • 4.8A, 120V disposal • 1,150W, 120V dishwasher • 10kW electric range Calculate the service demand load for the entire dwelling. The service is 120/240-volt, single-phase. Round the answer to the nearest whole number.

306641 VA

A multifamily dwelling has 12 units with 1,050 square feet each. What is the ungrounded (or line) feeder demand, in volt-amperes, for the lighting, small appliance, and laundry load when no general laundry facilities are planned for the premises? Round the answer to the nearest whole number.

34080