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I'm looking for a 20A 2-pole breaker for a Siemens panel. I see two options that offer high amounts of arc-fault and ground-fault protection. I don't understand the difference between these options however.

A. Siemens 20-amp 2-Pole Combination Arc Fault Circuit Breaker This 'regular' version is slightly more expensive and has a short white (I presume neutral connector) wire coming out the back

B. Siemens QAF 20-amp 2-Pole Combination Arc Fault Plug-on Neutral Circuit Breaker This version differs in its name having "QAF" and "Plug-On", it's slightly cheaper, and the back looks like most circuit breakers.

I've found it surprisingly difficult to learn what QAF stands for and what the different use-cases for these two options are. Could someone explain the difference between these two devices and when each is most appropriate to use?

In my case this would be used for a 250V appliance with a 20A load. I expect two hot wires to come off each pole of the double-pole breaker and one shared neutral returning to the panel/CAFCI breaker, along with a ground for the circuit. I have used GFCI and AFCI breakers before but CAFCI is new to me - I see it is the recommended norm for safety reasons and I'm happy to get on board with that.

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    There are different types of Siemens panels. So the first thing to do is figure out what panel you have and which breaker(s) are compatible. Upload pictures showing the existing installed breakers and showing any panel labeling/diagram - often on the inside of the door/cover. Commented Dec 15, 2022 at 16:31
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    Siemens plug-on electronic breakers - wiring made easier! CAFCI breakers now have a single load lug(s) only. Wiring made easier with the neutral lug removed. These breakers can be installed in the same manner as the thermal magnetic breakers. This allows the installer to land ground and neutral conductors in the load center before installing the breaker and load conductor. The new design allows for the same reliable installation method using the neutral clip as the line side clip. The small footprint allows for over 4 inches of wire bending space.
    – Traveler
    Commented Dec 15, 2022 at 18:23
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    Functionally the did the same, the difference is in installation method : Plug-On Neutral, Plug-in or Bolt-on
    – Traveler
    Commented Dec 15, 2022 at 18:40

1 Answer 1

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What is CAFCI?

CAFCI is the more proper word for an AFCI. Dollars to donuts you already installed a CAFCI the last time you installed an AFCI. "C" stands for "Combination" and means it detects 5 types of arc fault instead of just 2-3 types.

Say what??? Well for safety, shorting arcs between wires need to be detected at the breaker. But inline arcs across bad wire connections can be detected at the first receptacle. So it was allowed to have split arc fault detection. However as products evolved that became silly and it became cheaper to do it all in one device, hence the CAFCI being an irrelevant distinction now.

AFCIs use the power of computer processing, so it's no surprise that this technology moved fast.

What is PON or Plug-On Neutral?

You have two models there:

  • Q220AFCP
  • Q220AFCNP

The difference is the "N" in the model number. The "N" denotes "Plug-On Neutral".

Plug-on Neutral breakers only work if you have a Plug-on Neutral panel. If unsure, pick the non-PoN.

Now, remember the last time you installed a breaker? You screwed down the clamp to hold the wire, and then you also used an insulated screwdriver to screw the contact end of the breaker down to the energized bus? No, you do not remember that last part?

No, since modern panals are not bolt-on... they are plug-on with respect to the breaker's connection to the "hot" bus. The only bolt-on consumer panel was Pushmatic, and it is obsolete. (not because of that; it is revered for that bolt-on feature actually. Because guess what? Plug-on connections are not 100% reliable. They do fail.

GFCI and most AFCI breakers need neutral. So the "Plug-On Neutral" or PoN feature on panels rearranges the neutral bar so the breaker can plug-on to the neutral instead of bolt-on. This feature saves the installer 5 seconds per breaker. That is what PoN does. As you may gather, this is marginally useful for builders who install 500 breakers a day... and absolutely useless for DIYers, for whom 5 seconds makes no difference at all.

It is also useful for marketing because they can say "our panels have this, the competitor's don't" - though not really anymore. Why you might want that feature, I've already explained.

I get free ground-fault protection too, right?

The purpose of AFCI or arc fault protection is to prevent fires from wires arcing and making heat.

GFCI (Ground Fault protection) is a completely different thing. It protects humans from being shocked. In North American wiring, that is the primary goal of GFCI protection, so it is set to a sensitive (high level of protection) threshold of 5 milliamps, which won't even stun you. (if a ladder or water is involved, a stun may be a kill). They also make a weaker (less sensitive) version called a GFPE (Ground Fault Protection for Equipment) aka RCD (Residual Current Device) in Europe at 30mA threashold - reducing sensitivity reduces nuisance trips but doesn't protect humans as well.

CAFCIs (Combination AFCIs) do not include GFCI protection. "Combination" does not mean that.

They do make a thing that is both AFCI and GFCI. It is typically called "Dual Mode" and says so flat-out.

That said... remember I said there are 5 types of arc faults? Arcing between hot and ground wires, or between neutral and ground wires, are also ground faults. One option for an AFCI to detect those two modes is to include GFPE, i.e. "be a weak GFCI". And those AFCIs require the neutral wire for that purpose.

So your AFCI might have an internal GFPE, but it does not meet any legal requirements for GFCI.

Why not be a weak GFCI when they could be a strong GFCI with a minor tune? Because strong human-rated 5mA GFCIs are far more prone to "nuisance tripping". That's why, in Europe where they put an RCD on the whole house or large parts of it, they detune to the 30mA threshold because a house may have more than 5mA of natural leakage just from capacitive coupling and other normal effects.

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  • Very helpful, thanks. It sounds like the non-PoN version is best in my case, and that the non-PoN would be compatible with any Siemens panel whereas the PoN version is only compatible with certain models - am I understanding that correctly?
    – cr0
    Commented Dec 15, 2022 at 19:22
  • @cr0 yes, and I added a section on the GFCI question. Commented Dec 15, 2022 at 19:27
  • Thanks. No water nearby in this application. Interesting to know that even this CAFCI is not the 'highest level of safety' for a breaker.
    – cr0
    Commented Dec 15, 2022 at 19:44

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