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Old 01-27-2009, 01:47 AM   #46
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Back to the original arc flash issue. I had heard about this but was under the impression it was rare enough in residential aps that i didn't need to worry about it. I did some reading and it seems most agree that with voltages under 240 and "typical" residential POCO setups, it's not a concern. Exceptions are discussed, however, like rural areas where the transformer may be a long way from the house.

Question to the pros (or anybody else): Have you ever seen an arc flash from a residential panel? Ever had someone you know personally experience one? I try to stand aside and not look directly at breakers when I flip them on, but if I need to be more careful than that, I'd like to know.

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Old 01-27-2009, 05:37 AM   #47
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Well that's what it boils down to. People who make money doing wiring don't want homeowners taking work away from them. It's never about safety, it's always about money.
you can veiw it that way if you want. but when you have fixed as many screw ups as I have,,,, seen how many came close to causing fires. and when you know a family (both parents, 3 children ages 8, 6 and 13 months) that died in a house fire as a result of a "previous home owner's" electrical work, (which was not inspected) it makes you have a different veiw on things. Around where I am, getting an inspection for any wiring alteration is the law, and do you really think they made that to only apply to licenced professionals who do the work every day? yu want to do the work, hey no problem, just follow the rules, and get it inspected.
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Old 01-27-2009, 06:17 AM   #48
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Originally Posted by philS View Post
Back to the original arc flash issue. I had heard about this but was under the impression it was rare enough in residential aps that i didn't need to worry about it. I did some reading and it seems most agree that with voltages under 240 and "typical" residential POCO setups, it's not a concern. Exceptions are discussed, however, like rural areas where the transformer may be a long way from the house.

Question to the pros (or anybody else): Have you ever seen an arc flash from a residential panel? Ever had someone you know personally experience one? I try to stand aside and not look directly at breakers when I flip them on, but if I need to be more careful than that, I'd like to know.
I have personaly not seen one from a residential panel, how ever the charactoristics of breakers for tripping on a short, it can take up to a second for the action to complete, from what I have read on testing that has been done you can get a couple thousand amps instantainously for that second, you may think so what, a flash of light for a couple seconds but its not that that gets you, is the flame, which with residential voltages is considerably smaller, and the ejection of molten metals, kind of like whats happens with welding with a bit of a bang behind it propelling the melted materials outwards. I have ecountered damaged equipment from short circuits and seen where a section of rigid conduit blown/melted away where it entered a splitter large enough that I could put 2 fingers through the hole, witnesses said the sparks flew about 40 feet, there was a black spot on the wall that covered probley 10 square feet, about 3 square feet of paint was scorched off the block wall one 3/0 cable was completey melted off with about 2 inches missing the others the insulation was melted for about 12 inches. the whole thing took less than a second just a very loud bang and extremely bright flash of light , was a 200 amp feed at 600 volts, to a splitter which fed a couple machines, one cable shorted to ground where it emerged from the pipe due to a missing bushing and a sharp pipe edge combined with years of vibration, 600 volts is only 347 to ground, basically 3 times the 120 v to ground in a residential panel, so from that I would say that a bad residential short could be dangerious at the least for anything in very close proximity. know what are the hazzards is the key to being safe, I've spent over 20 years in this trade without major incident, not saying that it can't or won't happen, but I am still carefull every day, look for the potential, and take the apropriate steps to avoid an accident.

What your doing is correct, keeping a distance and out of the direct path if somthing did occur you would be "safer"

Last edited by ACB Electric; 01-27-2009 at 06:21 AM.
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Old 01-27-2009, 10:45 AM   #49
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As a homeowner that works on my own house, I'd love to hear what some of those mistakes are so I don't make them too... I like my kids! (usually. :-)
Splices not made in boxes. Splices made by twisting the wires together with no clamp or wire nut, then covered with tape. Speaker wire used as conductors on the lighting circuits. Thin wall conduit poked inside the light fixtures without connectors - sharp edges. Wire to small for the ampacity of the circuit breaker ie 18 ga speaker wire on a 20amp breaker. Welding receptacle outlet hanging from the NM with no box and not secured. Grounding conductors just twisted together loosely, a multi wire circuit with 3 hot wires and 1 nuetral (on a single phase supply). A switch on a neutral wire. All in a 2 car garage/workshop.
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Old 01-27-2009, 10:49 AM   #50
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Holy crow!!! Ok, I know I'm not an expert, but I guess it's like anything else, if you know enough to know that you don't know everything, then your well beyond the average joe. I'm actually trying to figure out the 3 hot wires on a multi-wire circuit, how do you even do that. :-)
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Old 01-27-2009, 11:06 AM   #51
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Originally Posted by philS View Post
Back to the original arc flash issue. I had heard about this but was under the impression it was rare enough in residential aps that i didn't need to worry about it. I did some reading and it seems most agree that with voltages under 240 and "typical" residential POCO setups, it's not a concern. Exceptions are discussed, however, like rural areas where the transformer may be a long way from the house.

Question to the pros (or anybody else): Have you ever seen an arc flash from a residential panel? Ever had someone you know personally experience one? I try to stand aside and not look directly at breakers when I flip them on, but if I need to be more careful than that, I'd like to know.
Just because something is rare doesn't mean it can't happen. I was called out on a job to replace the bus bars in a panel. The homeowner had somehow managed to bridge the buses with a large screw driver. The molten metal from the bus and from the screw driver had covered his glasses and burned his hand. The flash started his shirt on fire and temporarily blinded him. He did not receive a shock and the main breaker did not trip. Luckily the screw driver was blown free. He said it was over in just a split second. I replaced the entire panel and main circuit breaker. This was a typical city type 200 amp service with about 4 homes on each transformer.
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Old 01-27-2009, 11:18 AM   #52
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Lack of arc flash incidents in residential panels isn't due to lack of possibility. Arc flash occurs more often where major work is being performed. If just replacing a single pole snap in breaker, not much can go wrong. Replacing a 3 pole bolt on is different.

Make no mistake. A 240 V residential panel can blow melted bus bar into your face just as readily as any industrial setup. The laws of physics don't care whether or not it is in your house or office.
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Old 01-27-2009, 11:46 AM   #53
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Well that's what it boils down to. People who make money doing wiring don't want homeowners taking work away from them. It's never about safety, it's always about money.
Supposedly licensing and regulation are to protect the public. How much safety, reliability and function you get per tax dollar spent is pretty variable.

When I took my home improvement test in MD, there wasn't a single question on it about driving nails or replacing faucet washers; it was all business law for the Fed and the State.

What they do is, if I wreck somebody's house there is a fund that guarantees homeowners reparations, so it's kind of after-the-fact. I'm considered competent until proven otherwise.

This wouldn't work for airline pilots.
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Old 01-27-2009, 06:57 PM   #54
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Well that's what it boils down to. People who make money doing wiring don't want homeowners taking work away from them. It's never about safety, it's always about money.
I disagree with that. To broad of a brush. I have a much bigger problem with jack leg hacks doing work for people who think they are actually getting an electrician, than I have with home owners doing DIY projects. I also have issues with big box stores giving home owners bad advice and information because they lack the training to give out accurate advice.

More and more the country is requiring permits and inspections. If a home owner has his work inspected by a qualified electrical inspector, he is in pretty good shape. But up until recently a DIY person had no way of knowing if what he had done was ok or a serious hazard to life safety.

A lot of us on this forum are legitimate contractors helping home owners do the job efficiently and safely. But we all have to realize, not every home owner has the skills required to do certain tasks. Even with good advice.

To stick the "it;s all about money" label on all contractors or tradespeople is just as wrong as some of the wiring I see.

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