Motor Conductor sizing

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dtaylor6347

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A question on 310-16 as related to motor branch circuits. I have a 1 phase 120VAC 5HP motor with a 1.24 S.F. and 40 Degree C Temp. Rise. I calculated this out to a size #14 AWG according to the 60 Deg. Col. and a 30A C.B. Now my question: the oblisk listed by the allowable ampacity, does this apply to this calculation? I saw that the code references 240.4(d) and refers me to table 240.4(g). I see the motor section listed here but I don't see any specifics in the section that states it is o.k. to use a 30A C.B. in this application. Am I missing something or is this inferred from the Motor section being listed in the 240.4(g) Table?
 
At 120Volts a 5 hp motor will draw 40 amps (see name plate) conductor sizing X 125% is 8 conductor for a 60 degree ampacities must be utilized and therefore larger conductor sizes maybe required. I calculate a 60amp overcurrent protection.
Just my $.02
 
David,
At 208volt a 5hp motor FLA is 16.7amp (name plate) X 125% = 20amps, with 12ga wire. A 30amp breaker is acceptable.
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If the 125% of FLA really was 20 amps, then a #14 would be permitted for this application, however it is 20.875 amps and does require a #12. IAlso the breaker can be up to 250% of the FLA so a #12 on a 40 amp breaker is code compliant.
Don
 
I see the motor section listed here but I don't see any specifics in the section that states it is o.k. to use a 30A C.B. in this application. Am I missing something or is this inferred from the Motor section being listed in the 240.4(g) Table?
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It is not infered, it is specifically permitted. 240.4(D) says that the overcurrent protection rules found in Article 430 apply to the motor conductors.
Don

edited to fix quote
 
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dtaylor6347 said:
Sorry, that was supposed to be 208 VAC 1.5 HP ...

Table 430.248----208 volt Single Phase 1.5 HP =11 amps x 125% =13.75 amp rated conductor = 14 AWG.
CB @ 250% MAX 27.5 = 25 amp breaker

How do you other guys get that quote area to be in a blue square so it stands out?
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Look at Don's post right above your's. He screwed up on it. In the first box that looks like this, [/quote] he shouldn't have the / in it. The first bracketed box should be quote and the second should be /quote
 
ryan_618 said:
Look at Don's post right above your's. He screwed up on it. In the first box that looks like this, ---- he shouldn't have the / in it. The first bracketed box should be quote and the second should be /quote
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Got it,
Thanks Ryan
 
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