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"Welding with AFCI's"!

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  • "Welding with AFCI's"!

    I don't trust these things as far as I can throw them. Been through product re-calls etc. What do they do?

    I tried to come up with a "real world" test. If I connect a tiny single strand of wire to hot (black) and then rub a std light bulb against the EGC I can create a rather impressive arcing situation that the AFCI immediatly "takes care of". Fine - Great - I am impressed.

    Try same thing rubbing light bulb against neutral (white) - you can create amazing light show of sparks. NOTHING happens. Make things even worse - just full on contact w/o light bulb. Doesn't even trip the breaker like a normal breaker would. Huge spark and strand of wire blows up. Circuit just thinks everything is beautiful.

    I understand that it has to be able to "live with" a little arcing like when you first make contact plugging something into a receptacle. But not tripping when a short makes enough current flow to fry a strand of wire into a ton of sparks that roll around on subfloor. Does that seem right?

  • #2
    Re: "Welding with AFCI's"!

    I think you're expecting that AFCI to be doing some things that it's really not intended to do at all. Here is an Excellent presentation of what an AFCI is intended to do and not do:

    What you've done basically is to just show that fine wire can be used as a fusible link. When you fried those tiny strands by far surpassing THEIR capacity and only their capacity to carry current, they acted as a mini fuse and disintegrated. They blew before the breaker had a chance to heat up and blow. Telephone systems in the days of mechanical relays had little fuses with exposed fine wires that did the same operation. I can't tell you how many single gang receptacle boxes I've opened up only to find wires that had melted off the insulation due to loose or improper connections that fortunately did not result in a fire inside the box. An AFCI would have sensed that arc fault and heat buildup and tripped, making the homeowner hire an electrician to come in and find out the cause. Even with the melting inside a metal box, the fact that the wires are inside and most of the connections are where the heat starts, that box is designed to keep that heat and potential fire from spreading to the surrounding wood framing or paneling, or other outer flammable surface. That's why you just can't use longer screws and attach a plate to an electrical box without FULLY enclosing the box from the outside. So there are a number of backups to help that AFCI do its job and not result in fire. Now, as for your experiments, please, please, stop playing with 120 v even if it's with fine stranded wire. Without safety glasses, that copper you heated up and had dancing around on the floor could easily have ended up bouncing up into your eye causing a burn. That's why sparkies wear safety glasses nearly all the time, but especially when they are working around and near live circuits. And despite most people's cavalier attitude about 120 v, and only "fearing" 240, 120 can and will kill you given the right set of circumstances such as being in direct contact with ground (a concrete floor, dirt outside, wet surface, arm to arm which goes through the heart, etc.). We'd like to see you continue to post and ask questions !!!
    Take care, Jim Don.
    PS Sorry for the length of the post, and hope it did answer your questions.


    • #3
      Re: "Welding with AFCI's"!

      Should have mentioned - used a DRY 8' stick of wood. Structure is dry.
      I still don't understand why the thing obviously "didn't like" the arcing to EGC and promptly took care of the situation.

      I guess I have to take their word for it that it can distinguish between the 2 and "makes a judgement call".

      I just have a real problem being forced to fork over $32 x 7 units (and will be far more when 2008 kicks in) and only thing that tells me it does anything that a regular breaker can do (or less) is a giant stack of paper from seller that few people can understand. Or a super expensive test tool of some sort.

      Every once in a while I have to cross those wires to remind myself what I'm dealing with so that I won't take any chances working live or something!