The NEC imposes a limit on medium-base incandescent lamps to prevent overheating and ensure safety.

To determine the highest-rated motor, we calculate the full-load current (FLC) for each motor:

1. 10 hp 208 V 3-phase: From NEC Table 430.250, FLC = 30.8 A.
2. 3 hp 208 V 1-phase: Using the formula FLC=hp×746Voltage×Efficiency×Power Factor\text{FLC} = \frac{\text{hp} \times 746}{\text{Voltage} \times \text{Efficiency} \times \text{Power Factor}}FLC=Voltage×Efficiency×Power Factorhp×746​, the FLC is approximately 18 A.
3. 3 hp 115 V 1-phase: Using the same formula, FLC = 34 A (approximately).
4. 5 hp 240 V DC: From NEC guidelines, FLC is approximately 20 A.

According to NEC Article 425.55, lampholders for infrared industrial process heating equipment are permitted to be operated in series on circuits of over 150 volts to ground. This allowance ensures the equipment can function safely and efficiently in industrial settings with higher voltage requirements.

The distance from the motor to its source is approximately 240 feet, based on the given voltage drop, conductor size, and starting current.

According to NEC Article 440.22(A), the ground-fault protection for a hermetic motor-compressor must not exceed 175% of the rated-load current. This ensures the motor-compressor is protected without causing unnecessary tripping under normal operating conditions.

According to NEC Article 424.3(B), fixed electric space heating equipment is considered a continuous load because it typically operates for periods of 3 hours or more. Motors, depending on their application, are often treated similarly in sizing and calculations.

According to NEC Article 430.8, when a controller is built into a motor as an integral part, the individual marking of the controller is not required, provided that all necessary data is included on the motor’s nameplate. This reduces redundant marking and simplifies identification.

The secondary current available from a 175 kVA, single-phase transformer with a 120/240 V secondary is 729 amperes, calculated based on the transformer’s full load capacity.

According to NEC Article 404.6(B), double-throw knife switches can be mounted with the throw in either a vertical or horizontal position, providing flexibility for installation based on the application.

According to NEC Article 490.30(A), documentation for the spacing between overhead conductors rated over 1000 volts must include factors such as conductor size, which determines the electrical and mechanical properties influencing spacing requirements.

• 125 percent: According to NEC 404.14(E), overcurrent protection for dimmers must not exceed 125 percent of their rated load to ensure safety and compliance.
• Other percentages like 110%, 115%, and 120% are not aligned with the NEC requirements for dimmer overcurrent protection.

According to NEC Table 400.5(A)(1), the allowable ampacity for a flexible Type SO cord with 3 current-carrying conductors is 20 amperes. This rating accounts for the heat dissipation limitations of the cord and ensures safe operation.

According to NEC Article 410.23, any combustible wall exposed between the edge of a luminaire canopy and an outlet box with a surface area of 180 square inches or more must be covered with noncombustible material. This requirement minimizes the risk of fire in areas where luminaires are installed.

Based on NEC Article 450.3(B) and 240.6(A), the primary overcurrent protective device must be sized at 200 amperes, as it is the closest standard size below the calculated maximum.

According to NEC Article 430.23(A), for wound-rotor AC motors rated for light intermittent duty, the ampacity of conductors between the controller and secondary resistor must be at least 75% of the motor full-load current. This reduction accounts for the lower duty cycle and reduced heating effects during intermittent operation.

According to NEC Article 470.3(B), resistors and reactors must have a minimum clearance of 12 inches from combustible materials to allow for safe dissipation of heat and to prevent fire hazards.

o determine the number of heating panels/units needed:

1. Panel Capacity: Most snow-melting panels are rated to cover 120 sq ft per unit (standard rating).
2. Total Area: Divide the total area by the coverage per unit: Units Required=Total AreaCoverage per Unit=1500 sq ft120 sq ft/unit=12.5 units\text{Units Required} = \frac{\text{Total Area}}{\text{Coverage per Unit}} = \frac{1500 \, \text{sq ft}}{120 \, \text{sq ft/unit}} = 12.5 \, \text{units}Units Required=Coverage per UnitTotal Area​=120sq ft/unit1500sq ft​=12.5units
3. Rounding Up: Since partial units cannot be installed, round up to the next whole number, resulting in 13 units.

• Formula for apparent power:

  $$S(\text{Apparent Power in VA})=I(\text{Current in A})\times V(\text{Voltage in V})$$

• Substitute the values:
  • Current ($I$) = 16 A
  • Voltage ($V$) = 115 V

  $$S=16\text{A}\times 115\text{V}=1840\text{VA}$$

• Final Value: The apparent power of the motor is 1840 VA.

According to NEC Article 470.3(B), resistors and reactors must maintain a clearance of at least 12 inches from combustible materials. This clearance helps to prevent overheating and potential fire hazards.

According to NEC Article 409.21, the overcurrent protective device for an industrial control panel circuit must account for the largest branch-circuit protective device plus 125% of the FLA rating of all resistance heating loads. This ensures adequate protection for both the control panel and the associated heating loads.

According to NEC Article 410.11, luminaires must be designed, installed, or equipped with shades or guards to ensure that combustible materials are not exposed to temperatures exceeding 194 degrees F. This requirement minimizes the risk of fire due to excessive heat.

According to NEC Article 422.31(A), for permanently connected appliances rated 300 volt-amperes or less or 1/8 hp or less, the branch-circuit overcurrent device (e.g., a circuit breaker) is permitted to serve as the disconnecting means, provided it is within sight of the appliance.

The correct size for the inverse-time circuit breaker to protect a 3-phase, 208 V, 50 HP squirrel-cage motor is 400 amperes, based on the motor’s full-load current and NEC requirements.

According to NEC Article 422.31(B), for permanently connected appliances rated over 300 VA, the circuit breaker must be within sight of the appliance. This ensures safety and accessibility during servicing or maintenance.

To calculate the feeder/service neutral load:

1. Line-to-Line Loads:
   • These do not contribute to the neutral load since the current flows between the phases.
2. Line-to-Neutral Linear Loads:
   • These contribute their unbalanced current directly to the neutral.
   • Linear Load Contribution = 200 A.
3. Line-to-Neutral Nonlinear Loads:
   • These contribute the full current to the neutral due to harmonic currents.
   • Nonlinear Load Contribution = 200 A.
4. Total Neutral Load:

   $$\text{Neutral Load}=200\text{A (linear)}+200\text{A (nonlinear)}=400\text{A}.$$

• Determine Full-Load Currents:
  Use NEC Table 430.250 for 3-phase motors operating at 208 volts:
  • Motor 1 (50 HP): 136 A
  • Motor 2 (30 HP): 88 A
  • Motor 3 (20 HP): 58 A
  • Motor 4 (10 HP): 32 A
• Apply NEC 430.24:
  • The feeder conductor ampacity must be sized for:

    $$1.25\times \text{Largest Motor Current}+\text{Sum of Other Motor Currents}$$

  • Largest Motor Current (Motor 1):

    $$1.25\times 136=170\text{A}$$

  • Sum of Other Motors:

    $$88+58+32=178\text{A}$$

  • Total Feeder Ampacity:

    $$170+178=348\text{A}$$

• Select Feeder Conductor Size:
  • From NEC Table 310.16, 500 kcmil THW copper has an ampacity of 380 A at 75°C, which is sufficient for the calculated ampacity of 348 A.

According to NEC Article 440.62(B), the total marked rating of a cord- and attachment-plug-connected room air conditioner shall not exceed 80% of the branch circuit rating if no other loads are supplied. This ensures the circuit is not overloaded and provides a margin for safe operation.

According to NEC Article 425.55, lampholders for infrared industrial process heating equipment are permitted to be operated in series on circuits of over 150 volts to ground. This allowance ensures the equipment can function safely and efficiently in industrial settings with higher voltage requirements.

According to NEC Article 406.12, tamper-resistant receptacles are generally required in specific occupancies to prevent tampering and improve safety. However, receptacles located more than 5 1/2 feet above the floor are exempt, as they are out of reach for children and less likely to be tampered with.

According to NEC Article 470.3(B), a thermal barrier is required if the space between resistors and reactors and any combustible material is less than 12 inches. This ensures safety by reducing the risk of fire from heat generated by these components.

Power to utilization equipment connected to a rotary-phase converter cannot be supplied until the converter is operational. This ensures that:

1. The phase conversion is working correctly.
2. The equipment receives appropriate voltage and phase balance.
3. The system is safe for operation.

NEC Article 455.8(A) ensures that this prerequisite is met to prevent damage or malfunction of the connected equipment.

According to NEC Article 430.32(A)(1), for a 25-hp motor with a full-load current of 32 A and a service factor of 1.15, the overload protection must be set to 40 amperes (125% of the full-load current).

According to NEC Article 404.2(B), switches or circuit breakers shall not disconnect the grounded conductor of a circuit unless they simultaneously disconnect all conductors of the circuit, including the ungrounded conductors. This prevents leaving ungrounded conductors energized while the grounded conductor is disconnected, which could create unsafe conditions.

According to NEC Article 410.50, the grounded conductor (neutral) must be connected to the screw shell of the lampholder. This reduces the risk of electric shock when replacing lamps, as the outer shell is less likely to be energized.

According to NEC Table 430.250, the full-load current (FLC) of a 5-HP, 3-phase, 230-volt wound-rotor motor is 15.2 amperes. This value is standardized for design, protection, and conductor sizing purposes.

According to NEC Article 400.7(A)(8) and Article 430.109(F), an attachment plug and receptacle can serve as the disconnecting means for cord-connected equipment. This is permitted because the plug and receptacle can be quickly and safely separated to de-energize the equipment.

• True: As per NEC 406.12, tamper-resistant receptacles are required in dental offices, which are considered public or healthcare spaces. This ensures safety, especially in areas accessible to the public.
• False: This option is incorrect because dental offices fall under the NEC requirement for tamper-resistant receptacles for added safety.

According to NEC Article 460.8(A), the conductors connected to capacitors in motor circuits must be sized to handle 135% of the rated current of the capacitor. This requirement ensures that the conductors can safely carry the current without overheating.

According to NEC Article 410.10(D), no parts of cord-connected luminaires are allowed within a zone extending 3 feet horizontally and 8 feet vertically from the top of the bathtub rim or shower stall threshold. This ensures that luminaires are kept at a safe distance to reduce the risk of electric shock.

According to NEC Article 404.14(C), snap switches rated 20 amperes or less that are directly connected to aluminum conductors must be listed and marked CO/ALR. This marking indicates compatibility with both copper and aluminum conductors and ensures the connections are safe and reliable.

• False: Transformers insulated with less-flammable liquids are not permitted in areas with voltages rated 45,000 volts or more in Type I or Type II buildings. This restriction is due to safety concerns related to high voltages and potential fire hazards.
• True: This is incorrect because the NEC does not permit such high-voltage transformers in these building types, even with less-flammable liquids.

• Formula for FLC of a DC Motor:

  FLC=HP×746Voltage.\text{FLC} = \frac{\text{HP} \times 746}{\text{Voltage}}.FLC=VoltageHP×746​.

• Substitute Values:

  FLC=100×746500=74,600500=164 amperes.\text{FLC} = \frac{100 \times 746}{500} = \frac{74,600}{500} = 164 \, \text{amperes}.FLC=500100×746​=50074,600​=164amperes.

• Result: The full-load current for a 100-HP, 500-volt DC motor is 164 amperes.

According to NEC Article 410.11, luminaires must be designed and installed to ensure that combustible materials are not exposed to temperatures exceeding 194 degrees Fahrenheit. This requirement minimizes the risk of fire caused by excessive heat from luminaires.

• Determine Full-Load Current (FLC):
  From NEC Table 430.250, the FLC of a 15-HP, 230-volt, 3-phase wound-rotor motor is 42 amperes.
• Apply Maximum Overcurrent Protection Factor:
  For wound-rotor motors, NEC Table 430.52 specifies a maximum of 150% for non-time delay fuses:

  $$FuseSize=FLC\times 1.50$$ $$FuseSize=42\text{A}\times 1.50=63\text{A}.$$

• Select the Standard Fuse Size:
  Per NEC 240.6(A), the next standard size fuse is 60 amperes.

According to NEC Article 408.18(A), a clearance of at least 3 feet must be maintained between the top of a switchboard and any combustible ceiling. This is to ensure proper ventilation, heat dissipation, and fire safety.

According to NEC Article 406.3(C), receptacles rated 20 amperes or less and designed for the direct connection of aluminum conductors must be marked CO/ALR. This marking ensures compatibility and safety when using aluminum wiring, which has different characteristics than copper.

According to NEC Article 406.12(A), all 15- and 20-ampere, 125- and 250-volt non-locking type receptacles installed in dwelling units must be tamper-resistant receptacles. This requirement helps to reduce the risk of electrical shock, particularly for children, by preventing foreign objects from being inserted into the receptacle slots.

According to NEC Article 410.30(B), incandescent lamps for general use on lighting branch circuits shall not be equipped with a mogul base if rated over 1500 watts. This requirement is intended to standardize lamp bases and prevent excessive power usage in lighting circuits.

According to NEC Article 404.4, in damp locations, a flush-mounted switch or circuit breaker must be equipped with a weatherproof cover to protect against moisture and ensure safe operation.

• 125 percent: According to NEC 404.14(E), overcurrent protection for dimmers must not exceed 125 percent of their rated load to ensure safety and compliance.
• Other percentages like 110%, 115%, and 120% are not aligned with the NEC requirements for dimmer overcurrent protection.