AFCI Breakers

[kwired]

Here is one of the comments on RCD's from
1998 NFPA-70 A98 ROP, Page 112
Log #1820
Comment by CMP member Nichols in part:

This is the response of a CMP member that had access to all kinds of test reports and UL fact finding papers, though he was a bit off with the one device per dwelling part, perhaps back then split buss panels were still common and he was thinking a RCD could be a sub main.
Manufacturers reps present at this meeting would take that back up to corportate and they would say 'oh ok also make our new AFCI breaker work like a RCD just in case the wind blows in that direction'

You can bet the manufacturers pushed back against that comment with any means possible. They wanted a return on investment for development of what they already had at the very least.

 

[Jraef]

AFCIs do NOT monitor the neutral circuit, they just USE it to power the electronics inside of the breaker. GFCI breakers monitor the neutral circuit, so the correct neutral path is crucial to its operation. For pure AFCIs the neutral wire of the circuit does not need to connect to the breaker. But if it is a DUAL FUNCTION AFCI/GFCI breaker, then the GFCI function must monitor the neutral.

AFCIs do NOT “contain a lower level GFCI function”, that is a common misinterpretation. There are two types of AFCI functionality: series AFCI and parallel AFCI. Most older AFCIs were only Series, but now most are “Combination”, hence CAFCI. Series AFCI watches for arcs across a broken connection, parallel AFCI watches for arcs going line to ground or line to neutral. Parallel AFCI is looking for arcs of over 30 mA, which is why people think it is like a GFCI. But it is not comparing line and neutral. It is just looking at the current signature on the hot wire to look for evidence of an arc in the way the colorant flows. The 30 mA is just a threshold below which it ignores. But a parallel AFCI could see current going to ground of well over 30mA and not trip, if that connection is not actually ARCING when it happens. That makes it very different from a GFCI (or RCD).

 

[don_resqcapt19]

AFCIs do NOT monitor the neutral circuit, they just USE it to power the electronics inside of the breaker. GFCI breakers monitor the neutral circuit, so the correct neutral path is crucial to its operation. For pure AFCIs the neutral wire of the circuit does not need to connect to the breaker. But if it is a DUAL FUNCTION AFCI/GFCI breaker, then the GFCI function must monitor the neutral.

AFCIs do NOT “contain a lower level GFCI function”, that is a common misinterpretation. There are two types of AFCI functionality: series AFCI and parallel AFCI. Most older AFCIs were only Series, but now most are “Combination”, hence CAFCI. Series AFCI watches for arcs across a broken connection, parallel AFCI watches for arcs going line to ground or line to neutral. Parallel AFCI is looking for arcs of over 30 mA, which is why people think it is like a GFCI. But it is not comparing line and neutral. It is just looking at the current signature on the hot wire to look for evidence of an arc in the way the colorant flows. The 30 mA is just a threshold below which it ignores. But a parallel AFCI could see current going to ground of well over 30mA and not trip, if that connection is not actually ARCING when it happens. That makes it very different from a GFCI (or RCD).

Some AFCIs still have a GFPE circuit and do monitor the neutral. All of the original ones did that because without GFPE they could not pass all of the tests required in UL 1699. About 10 years ago, GE found away to pass all of the tests without using the GFPE. At least two other manufactures has also done that. If the instructions say you can use two single pole AFCIs with handle ties for a multi-wire circuit, then that device does not have GFPE.