Conductor / OCPD Maximum Size

[davehawks]

This is probably a silly question, but I am curious if someone can provide me a definitive code reference for the following situation:

Branch-circuit load of 70A continuous (type of load not listed in 240.3).

Per 210.19, ampacity of conductors sized to 125% of continuous load (no ampacity adjustments applicable) / 70A * 1.25 = 87.5A.

Per 210.20, overcurrent protection shall not be less than 125% of continuous load / 70A * 1.25 = 87.5A.

Is there a specific code reference that defines the maximum size of conductors and OCPDs utilized?

My contention is that such a reference does not exist and that obvious factors affecting the maximum conductor / OCPD would be:
- Cost
- Lugs
- Load Requirements

Am I missing something here????

 

[iwire]

Re: Conductor / OCPD Maximum Size

I am not sure what you are driving at.

410.11 limits the size of OCP for certain appliances but you can run as large a conductor that you are willing to pay for.

 

[templdl]

Re: Conductor / OCPD Maximum Size

I always considered branch circuit protection to consist of identifying the load first as you have done. The, the conductor MUST be sized to carry that computed load.
After that the OCPD must be sized to protect that conductor. As such the OCPD is sized based upon the amp rating of the conductor. If there isn't an OCPD rating that is the same as the rating of the conductor you are allowed to select the next high standard rating OCPD, 240.4(B).
Based upon 87.5a with no cable deratings applied a 3AWG cable would be select based upon 75degC which has a rating of 100a and, as such, a 100a OCPD would be applied.