CodeReadyPrep

Daily code practice for electricians, plumbers & HVAC techs. Every answer cited to the code behind it. Independent study prep, not an exam board.

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Panel working-space width is not always 30 inches. It is the equipment width or 30 inches, whichever is greater. Equipment doors must open at least 90 degrees. Reference: NEC 2023 110.26(A)(2).

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@ecmmagazine A practical harmonics check: on a 4-wire, 3-phase wye circuit where the major portion of the load is nonlinear, count the neutral as a current-carrying conductor for ampacity adjustment. NEC 2023 310.15(E)(3); phase balance alone does not remove that requirement.

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@MikeHoltNEC D, any of these: NEC 2023 330.10(A)(1) permits Type MC cable for services, feeders, and branch circuits. Still check the cable's listing and the installation conditions; permission for a circuit type does not make every MC cable suitable for every location.

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Answer: A. 97.75 ft. The required fall is 24 × 0.25 = 6 inches = 0.50 ft. The upstream invert must be 0.50 ft higher: 97.75 ft. Reference: Trade math; Drainage invert arithmetic.

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A downstream connection invert is 97.25 ft. A 24-foot upstream run must slope at 1/4 inch per foot. What upstream invert is required?

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@ecmmagazine Before treating equipment as deenergized during testing, a qualified person must verify absence of voltage, including induced voltage and backfeed. Opening the disconnect alone is not verification. OSHA 1910.333(b)(2)(iv)(B).

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@MikeHoltNEC A useful detail in NEC 2023 810.21(J): a separate antenna grounding electrode must be bonded to the power grounding electrode system with at least 6 AWG copper or equivalent. A separate rod alone is not the complete grounding arrangement.

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On a pipe-slope question, write the pipe diameter and units before opening the table. Then match the row. Inches per foot and total inches of fall are different quantities. Reference: IPC 2021 Table 704.1.

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Answer: D. 65 A. The 75°C column assigns 65 A to 6 AWG copper. The conductor cannot automatically be protected at any desired breaker rating. Reference: NEC 2023 Table 310.16.

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What is the 75°C table ampacity of 6 AWG copper before adjustment or correction?

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Tight by feel is not the torque requirement. When a numeric terminal torque is indicated, use an approved means to achieve it and follow applicable instructions. A calibrated torque tool is one such means. Reference: NEC 2023 110.14(D).

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Answer: B. 30 A. The two same-leg resistive-load currents are in phase and add in the shared neutral: 15 + 15 = 30 A. This is not a correctly phased multiwire branch circuit. Reference: Electrical theory; 210.4.

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Two purely resistive 15 A loads at unity power factor are accidentally connected to the same leg of a 120/240 V system while sharing a neutral. What neutral current results?

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Read the exception after the general rule. Bathroom receptacle-circuit questions can turn on whether the circuit serves one bathroom or multiple bathrooms. Reference: NEC 2023 210.11(C)(3).

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Answer: D. 6 AWG copper. The 200 A overcurrent-device row specifies 6 AWG copper equipment grounding conductor before any other applicable sizing considerations. Reference: NEC 2023 Table 250.122.

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Can you explain this?
A wire-type equipment grounding conductor serves a 200 A breaker. What is the minimum copper size from the basic table?
A. 4 AWG copper
B. 2 AWG copper
C. 8 AWG copper
D. 6 AWG copper
Answer in replies

[CodeReadyPrep @CodeReadyPrep]

High water pressure is not automatically better. Where building static pressure exceeds 80 psi, the general rule calls for an approved pressure-reducing valve, with strainer, to reduce it to 80 psi or less. Reference: IPC 2021 604.8.

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Answer: D. 3/4 inch. Section 501.3 requires a drain valve at the bottom of the tank. Its inlet is at least 3/4-inch nominal iron pipe size, and its outlet has male garden hose threads. Reference: 2021 IPC 501.3.

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Can you explain this?
Under 2021 IPC 501.3, what is the minimum nominal iron pipe size of the drain-valve inlet on a tank-type water heater?
A. 1/4 inch
B. 3/8 inch
C. 1/2 inch
D. 3/4inch
Answer in replies

[CodeReadyPrep @CodeReadyPrep]

When a motor problem gives several currents, circle the largest before multiplying. Keep the 125% calculation on its own line, then add the remaining loads. Reference: NEC 2023 430.24.