Reply to thread

Message

<blockquote data-quote="TJ Cornish" data-source="post: 27608" data-attributes="member: 162">Re: Electrical safety question (xposted from PSW)Breakers have that high a rating meaning they can successfully disconnect a 10,000amp current without fusing together.&nbsp; This doesn&#039;t necessarily mean that every short is 10,000 amps.Though the current spike in a short circuit situation is surely a lot of power quickly, breakers still work on thermal mass - it takes time at any given overcurrent level to trip the breaker, which is why the branch breaker is usually what blows (if it blows) and not something upstream, as the branch breaker has the least themal mass.I&#039;ve watched an electrician friend of mine working on 277v lighting circuits live (gloves, insulated tools, etc), and have witnessed multiple shorts to ground without even the branch breaker blowing.&nbsp; My electrician friend commented that this has happened to him before (yes I know, he shouldn&#039;t be working on a circuit like this live, and I don&#039;t want to know how many times he&#039;s been in that situation).&nbsp; This kind of situation (arcing, not working on live circuits) is what has precipitated the arc-fault breaker, because in the regulator&#039;s minds, arcs that don&#039;t blow breakers are common enough to be a substantial safety issue.I certainly agree with you that the NEC is confusing and contradictory at best, and I&#039;d surely like fewer &quot;standards&quot; for plugs, but I&#039;m not sure if what you propose makes it simpler or more complicated.</blockquote>

[QUOTE="TJ Cornish, post: 27608, member: 162"] Re: Electrical safety question (xposted from PSW) Breakers have that high a rating meaning they can successfully disconnect a 10,000amp current without fusing together. This doesn't necessarily mean that every short is 10,000 amps. Though the current spike in a short circuit situation is surely a lot of power quickly, breakers still work on thermal mass - it takes time at any given overcurrent level to trip the breaker, which is why the branch breaker is usually what blows (if it blows) and not something upstream, as the branch breaker has the least themal mass. I've watched an electrician friend of mine working on 277v lighting circuits live (gloves, insulated tools, etc), and have witnessed multiple shorts to ground without even the branch breaker blowing. My electrician friend commented that this has happened to him before (yes I know, he shouldn't be working on a circuit like this live, and I don't want to know how many times he's been in that situation). This kind of situation (arcing, not working on live circuits) is what has precipitated the arc-fault breaker, because in the regulator's minds, arcs that don't blow breakers are common enough to be a substantial safety issue. I certainly agree with you that the NEC is confusing and contradictory at best, and I'd surely like fewer "standards" for plugs, but I'm not sure if what you propose makes it simpler or more complicated. [/QUOTE]

Verification