Wire mold short did not trip breaker

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Dmc16

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Sparta,nj,United states
I have been installing outlets in classrooms using wire mold. Found one today that was pinched against wire mold, (forgot bushing), arched itself apart leaving wire live and outlet without power.
Checking all outlets once install is complete they show proper wiring using plug tester.
Grounding conductor has been installed to wire mold box and outlet. Also to the extension box which is tied to 4" square in wall with the two screws that come with it.
Did not trip breaker? Although wire mold does support that it can be used as an egc.
Thoughts?
 
Dmc16 said:
I have been installing outlets in classrooms using wire mold. Found one today that was pinched against wire mold, (forgot bushing), arched itself apart leaving wire live and outlet without power.
Checking all outlets once install is complete they show proper wiring using plug tester.
Grounding conductor has been installed to wire mold box and outlet. Also to the extension box which is tied to 4" square in wall with the two screws that come with it.
Did not trip breaker? Although wire mold does support that it can be used as an egc.
Thoughts?
Click to expand...
Ah, an arcing fault will not necessarily draw a high enough current to trip a breaker magnetically. With arcing faults you very often get caught between a rock and a hard place, not enough instantaneous current to trip the beaker instantaneously and quite often not long enough in duration and of high enpugh current to trip a breaker thermally on overload. We would like an arcing fault to act like it is a bolted fault but they do not behave in the same way.
 
Thanks for the info. Makes sense I have seen this a few other times, where breaker in theory should trip but does not. I did go back today and double check that I had a good ground by measure voltage hot to ground, box wire mold etc just as a precaution. It all seemed to check out. Lesson learned!
 
Dmc16 said:
Thanks for the info. Makes sense I have seen this a few other times, where breaker in theory should trip but does not. I did go back today and double check that I had a good ground by measure voltage hot to ground, box wire mold etc just as a precaution. It all seemed to check out. Lesson learned!
Click to expand...

Considering that you had s. L-G arcing fault a GFCI we could have picked up the L-G current and cleared the fault. But it is hard to justify the added cost ft or GFCI protection with the anticipation of such events.
 
Dmc16 said:
...I did go back today and double check that I had a good ground by measure voltage hot to ground, box wire mold etc just as a precaution. It all seemed to check out.....
Click to expand...

Measuring voltages anywhere in the system will not tell you if you the EGC resistance is low enough to promptly clear an L-G fault. Without current there will be no voltage drop and by design the EGC does not normally carry current.
For that kind of assurance you need to use an ohmmeter with a low (1 ohm or less) scale. The best of these low ohm meters actually put several amps of current through the resistance being tested.
 
templdl said:
Considering that you had s. L-G arcing fault a GFCI we could have picked up the L-G current and cleared the fault. But it is hard to justify the added cost ft or GFCI protection with the anticipation of such events.
Click to expand...
The AFCI manufacturers don't want to hear that.
 
kwired said:
The AFCI manufacturers don't want to hear that.
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I did consider suggesting that but the manufactures have irritated me with boasting about how the AFCI was the greatest thing since sliced bread and we here on this forum have beat that subject to what we would like to think is its death. The greatest thing about the AFCI is its ground fault feature which was originally 30ma as I can recall as opposed to 5ma with the GFCI. But I"m.not sure where that is today. And is the term AFCI a fancy term for a GFCI with some foofoo dust spinkled over it.
 
templdl said:
I did consider suggesting that but the manufactures have irritated me with boasting about how the AFCI was the greatest thing since sliced bread and we here on this forum have beat that subject to what we would like to think is its death. The greatest thing about the AFCI is its ground fault feature which was originally 30ma as I can recall as opposed to 5ma with the GFCI. But I"m.not sure where that is today. And is the term AFCI a fancy term for a GFCI with some foofoo dust spinkled over it.
Click to expand...
Some of them no longer have GFP. The ones that do still have 30mA unless they are a combination AFCI/GFCI.
 
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