deration question

[skiprima]

I have 14, #12 thhn current carrying conductors in a 3/4" emt conduit in an ice cream shop. What size breaker can these conductors be on in the panel? Can they be used for this application or would a different size wire be needed. Not as easy as first thought.

 

[augie47]

14 current carrying conductors requires a de-rating of 50%. Using your 90? rating for#12 THHN at 30 amps, you adjusted ampacity for derating is 15 amps, so a 15 amp breaker.
Whether they can be used depends on the type and size of the load (continuous, non-continuous, motors ?? )

 

[skiprima]

thx auge

thx auge

but now the tough part of the question: can we use 15 amp breakers in a commercial installation or would I need to upsize the wires to # 10, to allow them to be on 20 amp breakers?

 

[Pharon]

Check your local NEC amendments, if there are any. In Massachusetts, you'd only have to de-rate to 70%, not 50%.

 

[augie47]

but now the tough part of the question: can we use 15 amp breakers in a commercial installation or would I need to upsize the wires to # 10, to allow them to be on 20 amp breakers?

The NEC will allow the 15 amp circuits providing the characteristics of the load allow. I have no clue as to any local amendments in your area.

 

[lielec11]

but now the tough part of the question: can we use 15 amp breakers in a commercial installation or would I need to upsize the wires to # 10, to allow them to be on 20 amp breakers?

There is nothing in the code that I know of that says you cannot use 15A breakers in a commercial installation. I see them all the time. But like Pharon said, check for any local ammendments or local laws that may be in effect.