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We have recently upgraded several of our circuit breakers to the new combination AFI units required by NEC. Our panel is full, however, so this means several of these AFIs are stacked next to each other. With the summer heat and window AC usage, we’re noticing nuisance tripping starting to occur across the various breakers. This occurs after hours of the breakers being on with a consistent load and do not appear to be triggered by a new load and are not an instantaneous trip. We’ve checked all outlets and everything is well connected and separated. The circuit load is also well below the 80% allowance. So our thought at this point is that the stacked AFI breakers are becoming too hot due to being stacked together and are leading to one or more to trip (would welcome additional advice/thoughts if that doesn’t sound like the problem to you).

Our theoretical solution: could we replace some of these circuits with typical non-AFI circuits and instead install an AFI-outlet on the first outlet of that circuit (thereby also protecting everything downstream)? Our thought is that would eliminate some of the stacked AFI breakers and the overheating issue while also still providing the AFI protection…

Offending Breaker Model: Siemens QA120AFC

MinnesotaHome
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    What is the current being drawn on each of the circuits? That is to say, have you crunched the numbers or CT clamped the wires and you're sure you simply aren't overloading it? – Harper - Reinstate Monica Jun 12 '21 at 05:04
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    I'd call the manufacturer of the circuit breaker before proceeding. If you read through some other AFCI-related questions on here, you'll find they are tricky to troubleshoot! The mfr might have some good advice. Problem might not be heat in the panel; it could be a false-positive arc trip from the air conditioners. Update your post with the breaker model, picture of panel, and consider getting a thermal camera pic of your panel if you think it's really heat-related. – Jeff Wheeler Jun 12 '21 at 11:29
  • Yes- we have done that. Each of these are 20 amp circuits that are currently loaded with between 850-1,200 watts each out of the possible 1,920 watts on each circuit (20 amps x 120 watts/amp x 80% safety factor). The full draw on the whole service is also below the full possible supply of the house.

    Additionally of note, these are all existing equipment items that we’ve had for the past few years and never had problems until the AFI breakers.

     – MinnesotaHome Jun 12 '21 at 11:32
  • @MinnesotaHome -- are any of the indicator lights on the front of the breakers on when they trip? – ThreePhaseEel Jun 12 '21 at 13:13
  • Nothing is on when it’s tripped. The AFI light will briefly illuminate when we reset the breaker. – MinnesotaHome Jun 12 '21 at 13:50
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    Code dose not require existing residential units to be upgraded. Only new construction is required or change of use for a structure. Heat is one problem others are anything that modifies the sine wave like speed control on motors, or electronic lighting control can also cause these newer breakers to malfunction. Just be aware heat is not the only issue and just because code requires them for new builds doesn't mean you have to update your panel and waiting until more bugs are worked out may save some headaches. – Ed Beal Jun 12 '21 at 15:26
  • bear in mind that if you're upgrading to AFCI breakers because you want to (not required on existing structures as Ed noted), moving to an AFCI outlet means that you're losing protection between the breaker and first outlet. The AFCI is designed to protect the house from wiring faults, so leaving wiring unprotected kinda defeats the purpose. – FreeMan Jul 12 '21 at 13:01

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Your solution would probably work just fine. Before proceeding with this check with your local electrical inspector and let him know what you want to do and why. If the inspector does not agree ask how he would resolve the problem. You could also add a branch panel to move some of these breakers out of the original box.

Gil
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  • General question - is it true that these breakers are generally not supposed to be stacked up against each other? If so- how do new construction homes handle their panels where almost every circuit is required to be an AFI? Do they just put in a panel that is twice as large as normal and skip every other slot? (That isn’t possible/apply to my house - just curious in general). – MinnesotaHome Jun 12 '21 at 11:37
  • @MinnesotaHome My new construction Colorado home has about eight of them all stacked together. Only a few circuits don't have an AFCI: the furnace, dryer, sump pump, in-sink disposal, and AC. – Phil Frost Jun 12 '21 at 13:30
  • SWAG If it is possible you can move the breakers around and place some that are not fully loaded next to those that are. – Gil Jun 12 '21 at 16:03