# Calculate



## Malywr (Jan 23, 2018)

I have question on calculation of conductor Ampacity if it comes at 125%. to 30.25 or 30.45A it is ok to round it down to 30A or has to be 31A and then needs to be wire one size up


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## 99cents (Aug 20, 2012)

You’re getting two things confused. I am not familiar with NEC but it will have a rule for rounding up or down strictly for ampacity. Then there will be another rule for rounding up for your fuse or circuit breaker.


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## Malywr (Jan 23, 2018)

99cents said:


> You’re getting two things confused. I am not familiar with NEC but it will have a rule for rounding up or down strictly for ampacity. Then there will be another rule for rounding up for your fuse or circuit breaker.




Yes I am confused at 125%
If 30.4 I round down I will use #10 conductor and 30A fuse if I round up to 31A I think I need 40A fuse and #8 conductor. Am I wrong? So when do we round down? Or always round up?


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## Mr. Lacarno (Jan 2, 2019)

NEC 220.5(B) is where you should look.


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## John Valdes (May 17, 2007)

https://www.mikeholt.com/instructor2/img/product/pdf/1208459493sample.pdf


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## Malywr (Jan 23, 2018)

Mr. Lacarno said:


> NEC 220.5(B) is where you should look.


And John 

Thank you everyone 


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## Dennis Alwon (May 9, 2009)

Be careful with the round up of .5. It works fine for conductor ampacity but if you are calculating the fill for a conduit using Table 9 then note 7 states to round up at .8 or greater



> When calculating the maximum number of conductors
> or cables permitted in a conduit or tubing, all of the
> same size (total cross-sectional area including insulation),
> the next higher whole number shall be used to
> ...


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## Malywr (Jan 23, 2018)

Dennis Alwon said:


> Be careful with the round up of .5. It works fine for conductor ampacity but if you are calculating the fill for a conduit using Table 9 then note 7 states to round up at .8 or greater




I understand... thank you for those tips and code # 


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