I saw a post about a motor OCPD and wondering what’s correct. 430.248 says FLC was 30.8 amps. It’s an Inverse time breaker so 250% of 30.8 is 77 amps. OCPD would be a 70a or 80a breaker. He says 240.4(b) applies and the next size up breaker could be used and an 80a could be installed. Is that correct? 240.4(b) says it allows you to upsize the breaker in relation to the ampacity of the conductor if a standard breaker doesn’t match it but most likely the conductors would be #8’s so they wouldn’t be rated at that 77 amps. The ampacity of the conductor isn’t 77 amps, so the way I read it is you couldn’t use the one size up to go to an 80 amp breaker and would need to use a 70a. Am I missing something?
Motor OCPD question
- Thread starter ammklq143
- Start date
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- Connecticut
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- Engineer
240.4(b) isn't relevant to the size of the motor OCPD.
430.52(C) says that the next standard size up (80A) can be used.
430.52(C) says that the next standard size up (80A) can be used.
Got it. Thanks for the explanation.
- Location
- San Francisco Bay Area, CA, USA
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- Electrical Engineer
240.3 points you to table 240.3, listing the OTHER ARTICLES that apply if appropriate. One of those is Article 430 for motor circuits.
Article 240.4 applies IF none of the other articles in Table 240.3 do. So since it is a motor, 240.4 is superseded by 430 (except as noted within 430).
Article 240.4 applies IF none of the other articles in Table 240.3 do. So since it is a motor, 240.4 is superseded by 430 (except as noted within 430).