Journeyman Electrician's Branch Circuits Flashcards

If the computation for branch-circuits yields a value of 3.1, how many branch-circuits should be installed?

Answer: 4

When calculating the number of branch circuits required, any fractional result must always be rounded up to the next whole number. This ensures that there is sufficient capacity to safely handle the calculated load, preventing overloading and ensuring compliance with electrical codes. Therefore, 3.1 branch circuits would necessitate installing 4 circuits.

What exactly is a single branch circuit?

Answer: A branch circuit supplying only one utilization equipment

A single branch circuit, as defined by electrical codes like the National Electrical Code (NEC), is a circuit designed to supply power to only one piece of utilization equipment. This dedicated circuit ensures that the specific equipment receives adequate power without being affected by or affecting other loads, which is crucial for safety and proper operation of high-demand appliances.

For twenty (20) baseboard heaters, each rated at 2,250 watts at 220-volts, single-phase, how many branch circuits of 40 amps, at 220-volts, are necessary?

Answer: 7

First, calculate the total wattage: 20 heaters * 2,250 W/heater = 45,000 W. Next, determine the maximum continuous load for a 40-amp, 220-volt circuit, which is 40 A * 220 V * 0.80 (for continuous load) = 7,040 W. Finally, divide the total wattage by the circuit capacity: 45,000 W / 7,040 W/circuit = 6.39 circuits. Always round up for safety, so 7 branch circuits are necessary.

Find the total area of a five-story building with 125 feet by 100 feet of outside space.

Answer: 62,500 sq. ft.

To find the total area of a multi-story building, first calculate the area of a single floor: 125 feet * 100 feet = 12,500 square feet. Then, multiply this single-floor area by the number of stories: 12,500 square feet/floor * 5 stories = 62,500 square feet. This calculation provides the total floor area for lighting load calculations.

Outside measurements of a swelling unit are 60 feet by 45 feet. How many 120-volt, 15-ampere general lighting brand circuits are need for the house?

Answer: 5

First, calculate the total area: 60 ft * 45 ft = 2,700 sq ft. For general lighting in dwelling units, the NEC typically requires 3 VA per square foot, so the total lighting load is 2,700 sq ft * 3 VA/sq ft = 8,100 VA. A 120-volt, 15-ampere circuit can supply 120 V * 15 A = 1,800 VA. To find the number of circuits, divide the total load by the circuit capacity: 8,100 VA / 1,800 VA/circuit = 4.5 circuits. Always round up, so 5 general lighting branch circuits are needed.

A minimum ampacity of: must be present in the branch circuit conductors feeding a 6 kW, 240-volt, single-phase water heater.

Answer: 31.25 amperes

First, calculate the current (I) using the formula I = P/V: 6,000 W / 240 V = 25 amperes. Since a water heater is considered a continuous load, the branch circuit conductors must be sized for 125% of the continuous load. Therefore, the minimum ampacity required is 25 amperes * 1.25 = 31.25 amperes.

What is the dwelling unit load per square foot?

Answer: 3 VA per sq. ft.

According to the National Electrical Code (NEC), the general lighting and general-use receptacle load for dwelling units is calculated at a minimum of 3 VA (Volt-Amperes) per square foot. This value is used to determine the minimum required electrical capacity for these common loads in residential buildings.

What is the MAXIMUM continuous load, measured in Volt Ampere, that can be protected by a 20 Ampere Rated Circuit Breaker on a 240 Volt, Single Phase Branch Circuit?

Answer: 3,840 VA

For continuous loads, the circuit breaker and conductors must be rated for 125% of the load. Conversely, the continuous load cannot exceed 80% of the circuit breaker's rating. Therefore, for a 20-ampere breaker on a 240-volt circuit, the maximum continuous load is calculated as 20 A * 240 V * 0.80 = 3,840 VA.

Determine the MAXIMUM number of 120-volt fluorescent luminaries (lighting fixtures), each requiring 1.6 amperes, that may be supplied from a 120-volt lighting branch circuit with a 20 ampere rating for a retail store.

Answer: 10

For continuous loads like lighting in a retail store, the circuit breaker and conductors must be sized for 125% of the load, meaning the actual continuous load cannot exceed 80% of the circuit's rating. A 20-ampere circuit can safely carry 20 A * 0.80 = 16 amperes of continuous load. Dividing this by the current per luminaire (1.6 A): 16 A / 1.6 A/luminaire = 10 luminaires.

When a load is continuous, the maximum current is anticipated to last for AT LEAST:

Answer: 3 hours

The National Electrical Code (NEC) defines a continuous load as a load where the maximum current is expected to continue for 3 hours or more. This definition is crucial for sizing conductors and overcurrent protective devices, as continuous loads require a 125% rating to prevent overheating and ensure safety.

Where flammable liquid-produced vapors or combustible liquid-produced vapors are or may be present in air amounts sufficient to form explosive or ignitable combinations, are those sites classified as class ____ hazardous?

Answer: I

According to the National Electrical Code (NEC), locations where flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures are classified as Class I hazardous locations. This classification dictates specific requirements for electrical equipment and wiring methods to prevent ignition.

The usage of liquid-tight flexible metallic conduit (LFMC) is not permitted.

Answer: where subject to physical damage

Liquid-tight flexible metallic conduit (LFMC) is designed for flexibility and protection against liquids, but it is not intended for areas where it will be subjected to severe physical damage. Its flexible nature makes it vulnerable to crushing or impact, which could compromise its integrity and the conductors within. Therefore, the NEC prohibits its use in such conditions.

Where the motor controller also serves as a disconnecting means, it shall open all _____ conductors to the motor.

Answer: ungrounded

When a motor controller also functions as a disconnecting means, it must be capable of opening all ungrounded (hot) conductors to the motor. This ensures that when the disconnect is operated, all sources of power to the motor are interrupted, providing a safe condition for maintenance or repair work by completely de-energizing the motor circuit.

The length of the box must not be less than ___times the trade diameter of the largest conduit entering the box when a pull box is to be installed and conductors of size 4 AWG and bigger are to be pulled straight.

Answer: eight

For straight pulls in pull boxes, junction boxes, and conduit bodies where conductors are 4 AWG or larger, the length of the box must not be less than eight times the trade diameter of the largest raceway entering the box. This rule, found in the NEC, ensures adequate space for conductors to be pulled without damage or excessive bending.

What is the MAXIMUM flexible chord length allowed for a recirculating pump motor on a swimming pool at a residence?

Answer: 3 feet

According to the National Electrical Code (NEC), the flexible cord for a recirculating pump motor on a swimming pool at a residence is limited to a maximum length of 3 feet. This restriction is in place to minimize the risk of damage to the cord and to ensure that the pump is located close to a suitable receptacle, reducing potential hazards in a wet environment.

The branch circuits delivering 125-volt, single-phase, 15- or 20-ampere outlets in a garage Area in terms of residential occupancies.

Answer: shall not supply any other outlets outside of the garage

The National Electrical Code (NEC) mandates that 125-volt, 15- or 20-ampere branch circuits supplying garage outlets in residential occupancies shall not supply any other outlets outside of the garage. This dedicated circuit requirement helps to isolate potential hazards and ensure adequate capacity for garage-specific loads, preventing overloads from other parts of the dwelling.