Ampacity adjustment/next size up rule

[Dsg319]

Wanting to be sure I have this correct, say I have four 30 amp circuits in a raceway (8ccc) 90c degree conductors. After ampacity adjustments (40x70%=28) my ungrounded conductors are now only good for 28amperes.

After this is applied is the next size up rule still allowed to be used and I could still use a 30amp OCPD, if all the requirements are met to do so?


OCPDs rated 800A or less. If you meet the three requirements of 240.4(B), you can use the next higher standard rating of OCPD listed in 240.6 (above the ampacity of the ungrounded conductors being protected).

 

[infinity]

Yes your calculation is correct. If the circuits are multi-receptacle circuits then the next size rule is not applicable but that likely doesn't apply to your example.

 

[augie47]

Provided the load does not exceed the calculated ampacity of the conductors.
Your example would not be correrct if the actual load was 30 amps.

 

[Dsg319]

Thanks, as for the calculated load. After ampacity adjustments does the conductor still need to be 125% of the actual load or just 100% after adjustments are made?

For example a 24 amp-continuous load maxes out a standard 30ampere breaker, so after ampacity adjustments and brings my conductor ampacity to 28 amperes which is no longer 125% greater ampacity than the continuous load. Is it still compliant?

 

[david luchini]

Thanks, as for the calculated load. After ampacity adjustments does the conductor still need to be 125% of the actual load or just 100% after adjustments are made?

For example a 24 amp-continuous load maxes out a standard 30ampere breaker, so after ampacity adjustments and brings my conductor ampacity to 28 amperes which is no longer 125% greater ampacity than the continuous load. Is it still compliant?

100% after the adjustments are made.

 

[Dsg319]

100% after the adjustments are made.

Thank you.