feeder size for motors

[mshields]

I've got a 40HP motor which has FLA according to the tables at the back of Art 430 of 52A.

125% of that is 65A. So I go to Table 310.16 in the 08 code and in accordance with Article 110.14(C)1 I use the 60degC column to find that #6 is good for 55A and #4 is good for 70A. So since Art 430.22 says I cannot be less than 125%, I use #4.

Here's my concern, a table I just came across long used at a certain company indicates that #6's should be used in this instance. Obviously I can't go wrong doing it my way, but I want to know if the table is correct?

Thanks,

Mike

 

[markstg]

I've got a 40HP motor which has FLA according to the tables at the back of Art 430 of 52A.

125% of that is 65A. So I go to Table 310.16 in the 08 code and in accordance with Article 110.14(C)1 I use the 60degC column to find that #6 is good for 55A and #4 is good for 70A. So since Art 430.22 says I cannot be less than 125%, I use #4.

Here's my concern, a table I just came across long used at a certain company indicates that #6's should be used in this instance. Obviously I can't go wrong doing it my way, but I want to know if the table is correct?

Thanks,

Mike

You used the 60 deg C column, they used the 75 deg C column. True you aren't wrong, just spending more of your clients money than required.

 

[augie47]

If you research 110.14(C) you will find your installation will probably allow the use of 75? ratings thus allowing a #6 THHN/THW/THWN etc).