Two Exaggerated Factors Keeping AFCIs in the Code


Batteries Not Included
United States
I came across this NFPA ROCM PDF from 2012:

What strikes me is how aggressively manufacturers and UL are trying to convince CMP-2 that 500 amps of short circuit current is common at the service disconnecting means and that modern breakers trip magnetically at over 300 amps.



Yet, with a bit of research both are proven unlikely.

For example even with a 10kva pole pig 1,777 amps is observed (page 4):

Time current curves of common breakers show a 6-7x magnetic pickup (105 amps):

Even UL admits their own test results are likely off...

If the CMPs were fed realistic values a simple table listing a maximum run length for each wire size would suffice while still providing complete arc fualt protection coverage.

romex jockey

Senior Member
UL doesn't care, they know they are held to zero standard.
NRTL's verify manufacturers standards , they do not create them as they did with the simulator.....
This one unprecedented leap saw the resignation of the majority of the original nema-afci task force.
Resulting in it's chair, Dr Joe Engel's 2012 IEEE dissertation & subsequent rop