Load Calculations Flashcards

According to NEC Table 220.12, what is the general lighting load in volt-amperes per square foot for a dwelling unit?

Answer: 3 VA/sq ft

NEC Table 220.12 specifies 3 VA per square foot as the general lighting load for dwelling units.

How many 20-ampere small appliance branch circuits are required by the NEC in the kitchen, pantry, breakfast room, and dining room of a dwelling unit?

Answer: Two

NEC 210.11(C)(1) requires at least two 20-ampere small appliance branch circuits for these areas of a dwelling.

What demand factor is applied to the first 3,000 VA of general lighting load in a dwelling unit per NEC Table 220.42?

Answer: 100%

NEC Table 220.42 specifies a 100% demand factor for the first 3,000 VA of general lighting and receptacle loads in a dwelling unit.

Per NEC Table 220.55 Column C, what is the permitted demand load for a single household electric range rated at 12 kW or less?

Answer: 8 kW

NEC Table 220.55 Column C permits an 8 kW demand load for a single household range rated at 12 kW or less.

What minimum load in volt-amperes must be included per NEC 220.52(A) for each laundry branch circuit in a dwelling unit?

Answer: 1,500 VA

NEC 220.52(A) requires a minimum 1,500 VA load for each laundry branch circuit included in a dwelling unit calculation.

Per NEC 220.60, when can the smaller of two non-coincident loads (such as heating and cooling) be omitted from a dwelling service calculation?

Answer: When both systems will not operate simultaneously

NEC 220.60 permits omitting the smaller non-coincident load when it is unlikely the two systems will operate at the same time.

For a 240-volt, single-phase circuit supplying a 30-ampere load, what is the calculated apparent power?

Answer: 7,200 VA

Apparent power = Voltage × Current = 240V × 30A = 7,200 VA for a single-phase circuit.

Per NEC 220.44, what demand factor may be applied to receptacle loads in office buildings that exceed 10,000 VA?

Answer: 50%

NEC 220.44 permits a 50% demand factor for receptacle loads in excess of 10,000 VA in commercial occupancies such as office buildings.

What is the required calculated load per linear foot of show window lighting per NEC 220.14(G)?

Answer: 200 VA

NEC 220.14(G) requires 200 VA per linear foot of show window when calculating lighting loads for retail display windows.

At what percentage of the continuous load must branch circuit conductors and overcurrent devices be rated per NEC 210.20(A)?

Answer: 125%

NEC 210.20(A) requires branch circuit conductors and OCPDs to be rated at not less than 125% of the continuous load.

Which formula correctly calculates true power (watts) in a three-phase circuit?

Answer: P = V × I × 1.732 × PF

Three-phase true power equals line voltage × line current × √3 (1.732) × power factor.

What simplified NEC calculation method can be used for dwelling unit service sizing as an alternative to the standard method?

Answer: Optional Calculation per NEC 220.82

NEC 220.82 provides an Optional Calculation that simplifies residential service sizing using a general load per square foot plus specific appliance loads.

Per NEC 220.61(B)(1), at what percentage of the ungrounded conductor load may the neutral load for household ranges be calculated?

Answer: 70%

NEC 220.61(B)(1) allows the neutral load for household ranges, wall ovens, and cooktops to be calculated at 70% of the ungrounded conductor load.

What is the minimum volt-ampere load that must be calculated per NEC 220.14(I) for each general-purpose receptacle outlet in a dwelling unit?

Answer: 180 VA

NEC 220.14(I) requires 180 VA per receptacle outlet when calculating general-purpose receptacle loads in a dwelling unit.

Per NEC 430.22, at what percentage of the motor's full-load current rating must branch circuit conductors for a single motor be sized?

Answer: 125%

NEC 430.22 requires branch circuit conductors supplying a single motor to be sized at not less than 125% of the motor's full-load current rating.

When sizing feeder conductors for multiple motors per NEC 430.24, how is the largest motor's current contribution calculated?

Answer: At 125% of FLC

NEC 430.24 requires the largest motor's full-load current to be multiplied by 125% when sizing feeder conductors for multiple motors.

What is the power factor of a purely resistive circuit, such as one supplying only electric heating elements?

Answer: 1.0

A purely resistive circuit has a power factor of 1.0 (unity) because voltage and current are perfectly in phase.

What is the maximum calculated load capacity in kilowatts of a 100-ampere, 240-volt, single-phase service entrance?

Answer: 24 kW

Maximum load = 240V × 100A = 24,000W = 24 kW for a 100-ampere, 240-volt single-phase service.

Per NEC 220.53, what demand factor may be applied when four or more fastened-in-place appliances (other than ranges, dryers, or HVAC) are served by the same feeder?

Answer: 75%

NEC 220.53 permits a 75% demand factor when four or more fastened-in-place appliances (excluding ranges, dryers, and HVAC) are on the same feeder.

Per NEC Table 220.42, what demand factor applies to general lighting loads above 12,500 VA in a commercial (non-dwelling) occupancy?

Answer: 50%

NEC Table 220.42 specifies a 50% demand factor for commercial occupancy lighting loads that exceed the initial 12,500 VA threshold.