The perfect combination of antiquated junk

peter d

Senior Member
Location
New England
Had an interesting service call today. Complaint of a breaker intermittently tripping and loss of power in a good bit of the house. We get there and see that the house has not been touched (electrically speaking) in decades. The panel is vintage FPE and most of the wiring is old BX. We turn on the offending circuit and hear a loud hum coming from the part of the basement. I get out my trusty T5 and see that the current shoots up to 65+ amps, but of course the trusty FPE breaker shows no sign of tripping. :roll: After a bit more sleuthing we find the offending short circuit in a DIY installed outdoor light gone wrong. All in all, I'm amazed that the house did not burn down with FPE breakers allowing high fault current (enough to make the cable hum) on old BX. Perhaps newer and more reliable breakers would have tripped faster but I'm not betting on it. :happyno:
 

user 100

Senior Member
Location
texas
I see to many that should have burned years ago, IMO.
I think the reason many old places w/bx don't go ahead burn up already and only smolder in spots is because of the saving grace provided by that thick steel armor and those steel boxes covering and concealing those crumbling rw conductors.

Say what you will but that old crap was more fire resistant than most of what we use in houses today and better at hiding hot spots.:D
 

user 100

Senior Member
Location
texas
All in all, I'm amazed that the house did not burn down with FPE breakers allowing high fault current (enough to make the cable hum) on old BX. Perhaps newer and more reliable breakers would have tripped faster but I'm not betting on it. :happyno:
The fact that it was mandated that bx had to have that bond wire added to it should be a telling sign about the old stuffs ability to carry fault current. However, with a good low r bx path and modern cbs vs. the non tripping garbage, one could probably rest easy.:)
 
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mbrooke

Batteries Not Included
Location
United States
Occupation
*
Had an interesting service call today. Complaint of a breaker intermittently tripping and loss of power in a good bit of the house. We get there and see that the house has not been touched (electrically speaking) in decades. The panel is vintage FPE and most of the wiring is old BX. We turn on the offending circuit and hear a loud hum coming from the part of the basement. I get out my trusty T5 and see that the current shoots up to 65+ amps, but of course the trusty FPE breaker shows no sign of tripping. :roll: After a bit more sleuthing we find the offending short circuit in a DIY installed outdoor light gone wrong. All in all, I'm amazed that the house did not burn down with FPE breakers allowing high fault current (enough to make the cable hum) on old BX. Perhaps newer and more reliable breakers would have tripped faster but I'm not betting on it. :happyno:
65 amps will pop a new breaker in a few seconds. FPE of course, has its own time current curve standard :lol:
 

peter d

Senior Member
Location
New England
So the 65A was coming back on the armor, the neutral, some combo thereof? What size breaker/wire was it, and 1p or 2p?
The hot was pulling 65 amps, breaker was 15 amp. Panel was too much of a disaster to start getting at the neutral, and given FPE's reputation, I wasn't about to start digging around in it.
 

rt66electric

Senior Member
Location
Oklahoma
12 ga or 14 ga ??

12 ga or 14 ga ??

I have noticed the "65 amp" on several troubleshooting occasions. It seems to be the max current that 12 ga wire can handle before melting itself into an "open". It also seems to be the same as the inrush on a 2 HP motor.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
65 amps will pop a new breaker in a few seconds. FPE of course, has its own time current curve standard :lol:
Looking at the curve for one brand of breaker the trip time for a 65 amp fault on a 15 amp breaker would be between 1.6 and 13 seconds. For a 20 amp breaker of the same type it would be between 3 and 22 seconds for the trip.
 
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mbrooke

Batteries Not Included
Location
United States
Occupation
*
Looking at the curve for one brand of breaker the trip time for a 65 amp fault on a 15 amp breaker would be between 1.6 and 13 seconds. For a 20 amp breaker of the same type it would be between 3 and 22 seconds for the trip.


But the breaker should still open, perhaps not in 2 cycles, but it still would not hold indefinitely like Peter D claims.
 

peter d

Senior Member
Location
New England
But the breaker should still open, perhaps not in 2 cycles, but it still would not hold indefinitely like Peter D claims.
The breaker was tripping but definitely far out of a safe time range according to the homeowner, enough to cause a loud, sustained hum in the basement when it happened. He said he would reset the breaker and it would trip again, but not instantaneously or even within 5 minutes.
 

iwire

Moderator
Staff member
Location
Massachusetts
But the breaker should still open, perhaps not in 2 cycles, but it still would not hold indefinitely like Peter D claims.
Peter did not claim that, I doubt he sat there for more than five seconds listing to that hum.

Talk to BigJohn he put FPE breakers under test and they passed.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Peter did not claim that, I doubt he sat there for more than five seconds listing to that hum.
It sounds like it was more then a few seconds, but yes, its not specific or relative:


The panel is vintage FPE and most of the wiring is old BX. We turn on the offending circuit and hear a loud hum coming from the part of the basement. I get out my trusty T5 and see that the current shoots up to 65+ amps, but of course the trusty FPE breaker shows no sign of tripping.


Talk to BigJohn he put FPE breakers under test and they passed.

The breakers BigJohn put under over current test were not the red handle breakers.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
The breaker was tripping but definitely far out of a safe time range according to the homeowner, enough to cause a loud, sustained hum in the basement when it happened. He said he would reset the breaker and it would trip again, but not instantaneously or even within 5 minutes.
Thats what I thought, it was more then 30 seconds if you were able to pull out an amp clamp.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Only a few seconds.



The current shot up almost instantaneously, there is no way I'm leaving a circuit with a dead short on a junk FPE breaker on for 30 seconds. :happyno::happyno:
Oh, ok, got it. So you put the amp clamp on the conductor and then turned the breaker on.


And the home owner told you it took some time to trip. But why do you think new breakers will hold 65amps for for some time?
 
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