Installing Arc Fault Circuit Interrupter (AFCI) Circuit Breakers.




The latest version of the nfpa 70 code (the National electric code) requires that new installations use the afci type breakers. My home is not new but I want that type of protection for it.

This installment requires certified personnel to perform. If you don't possess the experience and training then hire the right person.

Read on for my replacement of existing thermal magnetic breakers to afci.

Step 1: Opening the Panelboard.

My panelboard is quite small since my home is small. Just 4 screws and the cover is off. Inside you can see the 240volt surge suppressor, the standard breakers and the motor protectors for my air conditioning.

There are two types of electrical faults: arcing and bolted. Standard thermal magnetic breakers will pick up only the bolted type where two live or a live and neutral/ground make a solid connection. Afci combination breakers like what I purchased from will handle both types of faults.

Step 2: Replacing the Air Conditioning Breakers.

Each afci breaker has a wire to connect to the panelboard neutral and an output lug for the load neutral. I have 3 small air conditioning unit in my home and the total maximum running load is 12 amps. As per nfpa 70 article 440, a single 20amp double pole afci breaker will handle all 3 units. Also each of the motor protectors is rated up to 42000btu. The total btu for my units is 34000. One of my air conditioning units is an inverter type and this uses far less power than its maximum rating.

First I turned off the main breaker, the 70adp. I verified the conductors de-energized with my multimeter. I disconnected the motor protectors and removed the breakers.

Next I wired the load wires to a single motor protector. The motor protector I wired to the afci breaker. The white neutral wire I connect to a lug on the neutral bus. I socketed the afci into the panelboard and verified tightness of all connections.

I ran all 3 air conditioning units at their lowest temperature for half an hour and took thermal images. All temperatures on the breaker, motor protector and wire connection are good.

Now a single 20adp afci breaker and motor protector handles the 3 air conditioning units very well and within code requirements.

Step 3: Replacing 2 Single Pole Breakers.

The single Pole afci breakers have a white wire to the panelboard neutral bus and a dedicated neutral output lug. Just like the double pole breakers.

Here it is important to identify the neutral wire for each breaker and connecting that neutral wire to the respective afci breaker neutral output lug.

Using my clamp ammeter I located each neutral wire by switching on and off the breaker for each. I swapped out to afci one at a time.

Again I applied maximum load to both breakers after verifying tightness of all wire connections. The load for these breakers are very small and the thermal image reveal nothing of consequence.

Step 4: Completion

With new afci breakers in my panelboard I feel a bit safer should any electrical faults occur. This is a worthwhile upgrade for safety in any home!

There are many cases of nuisance tripping of AFCI however when I tested on my home devices using motors with brushes, they all worked perfectly. Perhaps it is the newer combination AFCI models I have at home but they have been reliable so far. IF you have nuisance tripping then thorough inspection of the building wiring and end devices should be performed before judging the AFCI as defective.

Monthly testing of each afci breaker will be performed as per manufacturer instructions. This is simply pressing the test buttons of each, resetting the breaker and confirming the led indicator of the type of fault.



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    7 Discussions


    6 months ago

    Thanks. I was able to buy these breakers at but wanted to know the best place to buy the panel as well.


    3 years ago

    those things can be pretty problematic. I'm an electrician and I feel they are too sensitive. they can trip with just the flip of a switch

    1 reply

    Reply 3 years ago on Introduction

    Provided the device is not defective, they will trip once there is a fault. Don't assume nuisance tripping. Investigate and clear any fault (incorrect wiring, defective end devices, interference from strong RF sources etc). Nfpa 70 has mandated use of these devices for certain applications. Don't be discouraged by unit cost. I even tested my breakers by using my black and decker hammer drill, shop vac vacuum cleaner and the washing machine: there was no nuisance tripping.


    3 years ago on Introduction

    I'm in the same boat as danchondo an electrician as well and think they are too sensitive. What if you want to run some power tools they always cause the afci to trip. Honestly I wouldn't bother with it, especially if you don't know what you're doing which I feel this instructable should stress more as it could be very dangerous to someone. You say you have certifications and experience that surpass electricians please put on the main page a warning so people don't think it's overly safe and easy to do so no one gets hurt.

    1 reply

    Reply 3 years ago

    Again you assume your wiring or end devices are in proper working order. Do not blame the protective device for disconnecting the load. It is acting for a reason. As for my certifications and experience, that information lies with my current and previous employers. It is bad information for you as an electrician to condemn any protective device based on its price or your perception of nuisance tripping.


    3 years ago

    This kind of installation is required to be performed by an electrician in my country and likely in other countries as well.

    1 reply

    Reply 3 years ago

    You are Correct. Luckily my certifications and experience surpass that of any electrician.