Should AFCI Trip Before GFCI? - Electrical - DIY Chatroom Home Improvement Forum

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Old 03-18-2013, 08:16 AM   #1
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Should AFCI trip before GFCI?

The way my house is wired is every outdoor outlet is fed from the adjacent room and each one is a separate GFCI. When I installed a whole-house generator last summer (derecho) I swapped out some of the breakers in the transfer switch for AFCI for appropriate places.

One of these places is a downstairs bathroom which also has an outdoor outlet with GFCI. I was doing some work in my crawlspace and had brought an extra CFL drop light in with me plugged into that GFCI. Somehow I managed to break the CFL. So I went a got a replacement and still had no light. Checked the GFCI and had no power. Turns out the AFCI had tripped.

Should the GFCI have tripped first? I an really only concerned because this GFCI is near the pool and I want to make sure it is working as it should.

So far this is the first time I have had an AFCI trip. I have read about nuisance tripping but so far I have not experienced it.


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Old 03-18-2013, 08:20 AM   #2
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In that case, I would have thought the AFCI would trip.
Bathrooms are not required to have AFCI protection.


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Old 03-18-2013, 08:44 AM   #3
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Originally Posted by jbfan View Post
Bathrooms are not required to have AFCI protection.
I know, but the jackleg that wired this house placed the bathroom on the same circuit as an adjacent bedroom's closet.
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Old 03-18-2013, 11:51 AM   #4
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A GFI and an AFCI are looking for different reasons to trip. A ground fault can exist without an arc or you can have arcing without a ground fault.

If you want to see if the GFI is working push the test button. Did the power go off?
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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Old 03-18-2013, 12:22 PM   #5
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Imagine two people standing near you. You tell one to raise his hand when you yell "electrocute" and you tell the other to raise his hand when you yell "spark".

Each will only raise his hand when you yell the appropriate word.

Same with AFCI's (detects sparks - cause of fires).
GFCI's detect someone being shocked and quickly shut off power to prevent that.

Circuit breakers and fuses detect too much electricity being used (wires can get hot and cause a fire) and shut off the electricity before that can happen.

Last edited by Billy_Bob; 03-18-2013 at 01:30 PM.
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Old 03-18-2013, 01:06 PM   #6
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AFCI's do detect ground faults, but at a higher trip level than GFCIs (roughly 30mA instead of 5mA). The intent is to detect ground faults that might cause a fire, not to instantly stop an electrocution in progress. The main function of an AFCI is to detect current waveform characteristics that look like an arcing fault, and apparently your light breakage tricked the AFCI into thinking that's what was happening.


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