Main Feeder: Condctor and breker size

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Nedhal Al-Faraj

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Hi gentlemen

I have read in EC&M web magazine an article written by Mr. Mike Holt about Motor calculations .See this link http://www.ecmweb.com/mag/electric_motor_calculations_part_2/index.html

The last example shows the main feeder size is 6 AWG (with ampacity of 65 A as in Table 310.16) and the breaker size for the same feeder is 80 A Breaker.

Is this permitted? I mean is it permitted that breaker size ampacity is larger than cable ampacity?

Is this applicable also for main breaker of houses? Which NEC article discusses Size of Main Breaker of Houses?
My Q assuming the houses contains Window Air Conditioners, Water pump, lightens?etc.

Thanks
 
This is why a comprehensive knowledge of the NEC is necessary for understanding ALL installations. Requirements for motors and other specific equipment are not the same as general conductor use. Carefully read all of Article 240 - specifically 240.4
 
I have read article 220 and soveld some examples on Dwelling Unit Calculations but the calculations in article ends with finding Main Feeder Conductor Size, What about the Breakere size for same feeder ?
 
Have you reviewed some of the examples in Annex D? Your questions are so broad that it would require a month of discussion.

Carefully read 230.90(A) for service overcurrent protection and 215.3 for feeder overcurrent protection.
 
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