Why aren't there more fires?

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
View attachment 10880

This MWBC fed some old K&T and has worked for some years. Individual 15 amp CBs installed as was the custom before enligtenment.

New shingles went on recently and vibration of work caused center post of lampholder in attic to shortcircuit to shell. Not sure how many times the renters reset the CB before they noticed smoke and melting of the cable near the panel.

We, my help, modified the wiring so a new model of CH AFCI has been installed. K&T is still a factor but MWBC is not, as we refed with a single circuit. Taps from somewhere to someplace may be a problem but he was supposed to have checked for those.

Two hours after he left we get the call that the AFCI had tripped. Stay tuned for hourly updates...
 
Was the MWBC completely elminated? with the amount of heat that melted the bK circuit the possibility of melting within the sheathing is great. No mark on the GC service/feeder====
 
ptonsparky said:
View attachment 10880

This MWBC fed some old K&T and has worked for some years. Individual 15 amp CBs installed as was the custom before enligtenment.

New shingles went on recently and vibration of work caused center post of lampholder in attic to shortcircuit to shell. Not sure how many times the renters reset the CB before they noticed smoke and melting of the cable near the panel.

We, my help, modified the wiring so a new model of CH AFCI has been installed. K&T is still a factor but MWBC is not, as we refed with a single circuit. Taps from somewhere to someplace may be a problem but he was supposed to have checked for those.

Two hours after he left we get the call that the AFCI had tripped. Stay tuned for hourly updates...
Click to expand...

I only wish that this happened 15 years ago while I was a sales and applications engineer for C-H. I knew the AFCI design engineers at that time personally and was privileged to be a BETA test sight. I know that I could have been able to give your issue some attention from the C-H engineers.
Having K&T wiring it is almost for certain that there is no EGC so that tripping the AFCI on GF would be very unlikely at best. As such the technology they is hosted about would be L-N arcing or series conductor arcing which they brag about unless there is a ground available of some sort.
I know I could have given your problem some attention should you not able to ID something that is obvious.
 
templdl said:
I only wish that this happened 15 years ago while I was a sales and applications engineer for C-H. I knew the AFCI design engineers at that time personally and was privileged to be a BETA test sight. I know that I could have been able to give your issue some attention from the C-H engineers.
Having K&T wiring it is almost for certain that there is no EGC so that tripping the AFCI on GF would be very unlikely at best. As such the technology they is hosted about would be L-N arcing or series conductor arcing which they brag about unless there is a ground available of some sort.
I know I could have given your problem some attention should you not able to ID something that is obvious.
Click to expand...

AFCI (and GFCI) breakers do not have a ground connection only a neutral and one or more hot connections. How is the ground involved in the detection of a fault using either of these devices?
 
All in all, an interesting service call. My younger help gained some experience. I am impressed with the latest CH AFCI diagnostics. We autopsied the original 15 amp and found the thermal portion burned in two. Still don't know how many resets that took. The breaker would still latch closed.
 
It is not involved in the detection of a fault, it may however be involved in the existence of a fault.

To trip a GFCI requires current to flow outside the hot and neutral conductors. If there is a EGC, either wire or raceway, present, that provides a potential path for that current.
Or a load with grounded metal connected to an EGC. If the fault can be confirmed to be in the wiring itself, then the current would have to be leaking through building structure or other paths to earth or another neutral. It can certainly happen, but it is less likely.
 
fmtjfw said:
AFCI (and GFCI) breakers do not have a ground connection only a neutral and one or more hot connections. How is the ground involved in the detection of a fault using either of these devices?
Click to expand...

Common faults are line to ground which is picked up by the 30ma gf element. The AFCI has been designed to detect undesirable in line arcing in a circuit as well as line to nuetral arcing all of which are amazing accomplishments to me and are dependent upon the electronics having the caspability to recognize the algorythims of an arc.
That is why I brought up the lack of an EGC in a K&T system and the AFCI's ability to detect and arc which does not involve a ground. As such the AFCI would depend upon its electronics in order to recognize if arcing is accuring. Such technology amaizes me and the example as described by the OP would present a great case study to me.
It has always been of my opinion that K&T wiring would be an excellent application for the AFCI if in fact they are able to detect arcing and simply arcing the ground faults.
 
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