# AFCI Main Panel and Standard in Subpanels?



## green4now (Jul 29, 2016)

I am working on a remodel and we are putting in a new main panel and converting the old main panel to a subpanel.

My question is whether anyone has tried using a 100AMP AFCI breaker in their main panel and then kept the existing, old-style breakers in the subpanel.

And the follow up is: did you pass inspection?

Thanks!


----------



## Arrow3030 (Mar 12, 2014)

AFCI only comes in 15 & 20 amp.


----------



## inetdog (Apr 13, 2016)

Arrow3030 said:


> AFCI only comes in 15 & 20 amp.


Another problem is that for parallel arcs AFCI really uses arc signature detection to enable a lower instant trip threshold, which is still a higher current than the nominal breaker current. That current threshold would still be far too high on a 100A breaker to provide AF protection to downstream branch circuits. 
For series arcs the current threshold for detection is lower than the breaker rating, but still too high to protect a smaller downstream circuit. 
So even if a 100A AFCI breaker existed it would not take the place of required branch breakers downstream. 

*GFCI* is a different situation, since the fault current detection is the same for all breaker sizes. (Higher current *GFP *upstream may not provide detection of 6ma faults downstream though.)


----------



## Arrow3030 (Mar 12, 2014)

Good point dog. Isn't it 3 of the last 9 cycles need a certain signature and be over 70A peak for parallel? 

To the OP, as long as you're not modifying the circuits in the original panel AFCI shouldn't be required. You can check that with the AHJ but requiring AFCI in this scenario would be a bigger deviation from NEC than is typical.


----------

