NEC Tables · Overcurrent Protection

Standard breaker & fuse sizes — 240.6(A)

The list every OCPD question ends at: the standard ampere ratings, and when you may round up to the next one.

Free · NEC 2023 · Updated
Standard ampere ratings — fuses and inverse-time breakers
10152025303540455060708090100110125150175200225250300350400450500600700800100012001600200025003000400050006000——
Exam trapOver 800 A the rounding flips: 240.4(C) makes you round DOWN. And 240.6(A) also lists 1, 3, 6, 10 — small fuse sizes people forget exist.

When a conductor’s ampacity lands between two standard ratings, 240.4(B) usually lets you round up to the next standard size — if the device is 800 A or less and the load isn’t cord-and-plug. That rule plus this list settles most sizing questions.

Standard Ampere Ratings
1015202530
3540455060
708090100110
125150175200225
250300350400450
5006007008001000
12001600200025003000
400050006000——

Values derived from the 2023 National Electrical Code for exam study. Verify installations against the adopted code and local amendments.

Race your codebook — 3 lookups on this table

Q1

A single hermetic refrigerant motor-compressor has a rated-load current of 40A and no branch-circuit selection current is marked on the nameplate. A standard dual-element fuse sized at 175% of the rated-load current is not a standard fuse size, and the next higher standard size is not sufficient to carry the compressor's starting current. Which section allows increasing the fuse rating above 175% (up to 225%) of the rated-load current to handle the starting current?

  1. A 440.22(B)(1)
  2. B 440.12(A)(1)
  3. C 440.22(A)
  4. D 440.32
Show answer & explanation

Correct: C — 440.22(A)

440.22(A) sets the base 175% rating for individual motor-compressor branch-circuit protection and its exception permits going up to 225% when 175% won't carry starting current. 440.22(B)(1) covers equipment where the motor-compressor is the largest load in a multimotor unit, not an individual motor-compressor circuit.

Q2

A technician sizing the branch-circuit protective device for one hermetic motor-compressor finds that 175% of the rated-load current lands between two standard nonadjustable circuit breaker sizes. Which section permits using the next higher standard ampere rating in that situation?

  1. A 440.10(A)
  2. B 440.22(C)
  3. C 440.22(A)
  4. D 440.22(B)(2)
Show answer & explanation

Correct: C — 440.22(A)

440.22(A) explicitly allows rounding up to the next higher standard rating when 175% doesn't correspond to a standard fuse or breaker size. 440.22(C) instead limits protective device ratings to values not exceeding the equipment manufacturer's specifications, a different constraint.

Q3

An electrician is sizing an adjustable-trip breaker where the adjusting means is fully exposed (no locked door, no sealable cover, no password protection) and the AHJ won't accept the adjusted long-time pickup setting as the breaker's rating. Which section requires that this breaker's rating be taken as its maximum possible setting?

  1. A 240.6(A)
  2. B 240.6(D)
  3. C 240.6(B)
  4. D 240.6(C)
Show answer & explanation

Correct: C — 240.6(B)

240.6(B) governs adjustable-trip breakers that don't meet the restricted-access criteria of 240.6(C), forcing the rating to the maximum setting. 240.6(C) is the closest distractor but only applies when access is actually restricted (sealed cover, bolted door, lock, or password); 240.6(A) covers fuses and fixed-trip breakers, not adjustable ones.

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Overcurrent Protection NEC guide Article 240 practice questions 41 questions
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