I am puzzled by a "double-lugging" of a CAFCI, made by Siemens on a newer residential construction. Work is done by a professional electrical contractor, in Southern California.

Does Siemens allows CAFCI to be double-lugged?

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  • Is it the fuzzy photo or are there three neutrals on that breaker?
    – isherwood
    Feb 9, 2020 at 19:47
  • Notice how all the wires are runted off to only, barely make it to their present breaker. No way to move anything around in this panel! @isherwood You do indeed see 3 neutrals, and 2 on all the other breakers. Those are the AFCI pigtails. Feb 9, 2020 at 19:56
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    See the fat black wires on top feeding the main lugs? What does the writing on those wires say about their size? 2 AWG Aluminum, that kind of thing? Feb 9, 2020 at 20:00
  • Can you post a photo of the nameplate on your air conditioner's outdoor unit please? Also, can you post a photo of the directory for your breaker panel, and are the heat, hot water, range, and dryer in this place gas or electric? (if the big 4 are all gas, I can easily see how an 80A main and feeder would be reasonable, even for a fairly large duplex) Feb 9, 2020 at 20:00
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    That other question does not appear to have posted. Was it here on diy or did you post it on electronics.se? Feb 9, 2020 at 21:10

2 Answers 2



Siemens QP breakers, with basically no exceptions, cannot be double-lugged the way you see there. Fortunately, this is easy to fix. All you will need is a couple of 12AWG stranded THHN pigtails (one black, one white) and a pair of wirenuts suitable for 3 12AWG wires each, as well as an inch-pound torque screwdriver to set the torque on the breaker lugs properly. Turn the breaker in question off, unfasten the wires from the lugs, nut each pair (black and black, white and white) together with its corresponding pigtail color, insert the pigtails into the correct lugs (black in the top lug, white in the bottom lug), and torque the lugs back down to the labeled torque values using your torque screwdriver.

  • I thought it was absolutely no exceptions. One screw: one wire, 'labeled' or not.
    – Mazura
    Feb 9, 2020 at 23:26
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    @Mazura -- there are a couple of oddities in the lug capacity chart for Siemens breakers, but they don't really affect us much. (Eaton CH and Square-D, both QO and HOM, are the types you run into that support double-lugging in a meaningful fashion) Feb 9, 2020 at 23:38
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    @Mazura At least not true for QO/QOB se.com/us/en/faqs/FA237923 QO and QOB breakers, 1-, 2- and 3-poles, are UL Listed and rated to accept the following wire sizes, solid or stranded (type B or C). 10A - 30A - Either of the the following: 1 wire per lug: (1) #14 - #8 AWG Aluminum or Copper 2 wires per lug: (2) #14 - #10 AWG Copper Feb 9, 2020 at 23:43
  • I'm looking for code. Harper says "It is illegal to put 2 wires on one screw." How do I attach 2 wires to one terminal screw on an outlet or light switch? - that doesn't apply to breakers?
    – Mazura
    Feb 9, 2020 at 23:44
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    @Mazura -- indeed not. the wire-binding screws found on 15A and 20A wiring devices are totally different beasts than the box lugs found on distribution equipment and the likes. Feb 9, 2020 at 23:46

The crux of your question is covered in this question. Looks to me "no"; The breaker isn't labeled for double lugging, and neither is the panel. However I see other work here that concerns me.

The panel is much too small. It's a 30-space panel and 31 spaces are already used (hence the double-tap). I have a feeling the AFCIs are new, but the panel is an old installation, and the electrician "saved you the money" of tearing up the wall a bit to install a 40-space panel. The old panel worked because of use of double-stuff breakers.

Some circuits shouldn't be on AFCI or GFCI (e.g. refrigerators), so if you can find 2 such circuits, you can convert them to a double-stuff breaker and free up a space so those 2 circuits can each have their own AFCI breaker. All AFCIs seems a little crazy, given the overstuffing of this panel.

Another option would be a sub-sub-panel fed from here, possibly in a different location. Stay with Siemens, so you can reuse those $40-each breakers.

Lastly, the electrician did the "neat-freak" thing of runting down all your wires so they only have just enough length to reach the breakers they're in now. That limits your ability to rearrange breakers for logic, or to make space for added features like generator interlocks or surge suppression. This panel would be super easy to add a gen interlock to if you ever wanted to.

  • It's better than a box of spaghetti. What should it look like?
    – Mazura
    Feb 9, 2020 at 23:51
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    @Mazura Every hot and neutral should be able to reach every breaker space in the panel. That'll entail a little bit of slack; just tuck it up or loop down and up. Feb 10, 2020 at 0:10

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