breaker and conductor sizing

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jimleadermewto

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when breaker size of a motor load is determined by 430.52 in the NEC, does the wire size need to be changed to match the new breaker size?
 
Re: breaker and conductor sizing

Size conductor by 430.22 and OCPD by 430.52

As outlined in your last post the 71/2 HP motor would have a #10 conductor with a 70 amp breaker. Should this breaker not hold then this could be increased to a 90 amp breaker and still use the #10 conductor.
:)
 
Re: breaker and conductor sizing

The purpose of the breaker is to only provide short-circuit and ground-fault protection. The conductors are protected by the motor overloads. This is one reason why the difference between overload and overcurrent needs to be fully understood.
 
Re: breaker and conductor sizing

Just my opinion but the wire size for a single motor is sized using motor table of article 430. To get the FLC and then 430.22(A) tells me to multiply the FLC from the motor tables by 125%.

EX: 10hp 3 phase 208V = 30.8 FLC
Applying 430.22 30.8 x 1.25 = 38.5 Ampacity

Looking at table 310.16

38.5 Ampacity lets round up to 40 amps (220.5(B))
and we will assume "THHN" and equipment rated at 75 degrees. 40 amps Ampacity = 8 AWG THHN

And for the OCD if you are using Inverse time breakers. 38.5 x 250% = 96.25 Amps. 240.6 tells me I can use a 100 amp breaker. Article 240.4(D) does not apply to motor circuits. Lets see what others have to say, I am just an apprentice.......

Kevin
 
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