Switch leg trips AFCI in off position, Why?

[JoeNorm]

I have noticed if I am making up a light fixture on an AFCI circuit with the switch OFF and I cut through the hot and neutral together, it will trip the breaker. Can someone explain why this happens? Thanks

 

[OldSparks]

In some online research, I found this:

A combination AFCI breaker provides protection against parallel arcing (line to neutral), series arcing (a loose, broken, or otherwise high resistance segment in a single line), ground arcing (from line or neutral to ground), overload, and short circuit.

Neutral to ground as you are cutting is the apparent culprit.

 

[ramsy]

making up a light fixture on an AFCI circuit with the switch OFF and I cut through the hot and neutral together, it will trip the breaker

You are the 3rd person in 20 years to demonstrate how AFCI’s pass UL1699/B.

When not tripping over false positives, or arc impedance, they trip over simple resistance.

Most AFCI’s will trip by holding bare EGC & Neutral in same hand, without touching each other.

 

[kwired]

If it is an AFCI that has a GFPE component to it, all of them once did, then it is tripping on neutral to ground fault. Though there likely needs to be at least 30mA of current flowing in the incident to make it trip, which there could be if there is other loads on the same circuit at the time.

 

[Knuckle Dragger]

I have noticed if I am making up a light fixture on an AFCI circuit with the switch OFF and I cut through the hot and neutral together, it will trip the breaker. Can someone explain why this happens? Thanks

 

[Malywr]

In some online research, I found this:


Neutral to ground as you are cutting is the apparent culprit.

I agree

 

[JoeNorm]

But in this case the hot is switched OFF, so not connected to anything, right? Or is the slight connection through the switch enough?

 

[Little Bill]

But in this case the hot is switched OFF, so not connected to anything, right? Or is the slight connection through the switch enough?

I've done this multiple times. You're cutting not just through the hot and neutral, but also through the EGC. The strippers/cutters cause a short between neutral and EGC. With the GFP built into the AFCI, it sees that as a ground fault and trips. The switch doesn't have to be on.
Newer (some) AFCI don't have the GFP function and wouldn't trip under these circumstances.

 

[ramsy]

If it is an AFCI that has a GFPE component to it, all of them once did, then it is tripping on neutral to ground fault. Though there likely needs to be at least 30mA of current flowing in the incident to make it trip, which there could be if there is other loads on the same circuit at the time.

While end-of-line outlets have negligible Neutral-to-EGC potential when properly wired & maintained, MWBC junctions certainly do increase potential between N-G, or energize loose / open neutrals per 300.13(B).

I believe Square-D, Siemens, & Eaton still make AFCI models with 30mA GFPE.

 

[Little Bill]

While end-of-line outlets have negligible Neutral-to-EGC potential when properly wired & maintained, MWBC junctions certainly do increase potential between N-G, or energize loose / open neutrals per 300.13(B).

I believe Square-D, Siemens, & Eaton still make AFCI models with 30mA GFPE.

Siemens do not, and AFAIK, at least some of Eaton's do not.

 

[ramsy]

Siemens do not, and AFAIK, at least some of Eaton's do not.

I believe Siemens 1-Pole 1-Switch CAFCI with Pigtail still has GFPE.

 

[Little Bill]

I believe Siemens 1-Pole 1-Switch CAFCI with Pigtail still has GFPE.

The pigtail version might, but the PON doesn't. There isn't even a place for the load neutral to land.