mbrooke
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- United States
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- Technician
Anyone read the recent FPE whistleblower write up in one of the trade rags ? , unfortunately it met it's demise in the woodstove here ...
~RJ~
I missed it
The perfect combination of antiquated junk
- Thread starter peter d
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I missed it
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Half a minute? I missed that.
EVERY breaker has a trip curve. I couldn't find one for FPE Stab-Loks on the web, because they ceased to exist before people put things like that up on the web, and besides, they were all lies anyway, that's what they got in trouble for.
But, to the point made by others, a basic 15A thermal mag breaker will NOT trip instantly on a 65A current "surge". On a few curves that I have for various brands, the trip time at 4x rated current should be within 2-7 seconds. So if it was longer than 7 seconds, then I agree that breaker was faulty.
What the big issue was with FPE that took them down was that they falsified their records to UL with regard to trip times on the Stab-Lok product lines, so when problems showed up in the field and UL investigated, they found the fraud and pulled their labeling of FPE breakers, then lawsuits followed. That doesn't mean EVERY FPE breaker is bad, but when a breaker is SUSPECTED of being bad, there is plenty of evidence to back up the suspicion. But that's not a reason to be suspect of every and all breaker trip curves out there. UL is very vigilant on this issue, especially since the FPE debacle.
mbrooke
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- United States
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- Technician
FPE breaker time current curves can be found here, but need to register for free:
http://www.electricalmanuals.net/manual-categories/low-voltage-equipment/breakers/fpe
http://www.electricalmanuals.net/manual-categories/low-voltage-equipment/breakers/fpe
- Location
- Massachusetts
I know I am not telling Jraef anything here just adding that each fuse does as well. It would be very difficult to start a motor or transformer if OCPDs instantly tripped at their marked rating.
That 10 amp garbage disposal the homeowner wanted might draw 60 amps for a few cycles when turned on.
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
That an OCPD is designed to absorb a spike is a given we all accept.
The duration of the spike is what is intriguing here....
Disposals assume nuisance trips from lower settings , yet ground faults of just the right impedance may hum the flight of the bumblebee.
I think most here have been witness to this , in fact i've even had customers place their phones near panels ,resetting their 'vocal breakers' for my listening pleasure :lol:
This is not a short duration event, not 2,3,5,7 seconds, doesn't quite seem proprietary to any one make/model either. One would think enough magnetic flux builds up for the handle rating to mitigate it within this time ?
Having been under the impression the thermal qualities were slow , the mag trip fast ,is apparently not quite right then?
So i'm imagining all those circuits, components ,devices, lamp cords ,wire nuts , egc's, etc designed for 15 amps suffering the ill effects of this.....?
Some of this is starting to sink in....>
Vs.>
modified mag trip
~RJ~
The duration of the spike is what is intriguing here....
Disposals assume nuisance trips from lower settings , yet ground faults of just the right impedance may hum the flight of the bumblebee.
I think most here have been witness to this , in fact i've even had customers place their phones near panels ,resetting their 'vocal breakers' for my listening pleasure :lol:
This is not a short duration event, not 2,3,5,7 seconds, doesn't quite seem proprietary to any one make/model either. One would think enough magnetic flux builds up for the handle rating to mitigate it within this time ?
Having been under the impression the thermal qualities were slow , the mag trip fast ,is apparently not quite right then?
So i'm imagining all those circuits, components ,devices, lamp cords ,wire nuts , egc's, etc designed for 15 amps suffering the ill effects of this.....?
Some of this is starting to sink in....>
Vs.>
modified mag trip
~RJ~
- Location
- Massachusetts
What problem are we trying to fix?
Are we trying to find a way to prevent the huge numbers of electrical fires used to prove the need for AFCIs that never really happened?
Keep in mind, regardless of Peters on site observations the circuit breaker did function and prevented a fire. The homeowner had reset it a number of times before calling in an electrician.
Are we trying to find a way to prevent the huge numbers of electrical fires used to prove the need for AFCIs that never really happened?
Keep in mind, regardless of Peters on site observations the circuit breaker did function and prevented a fire. The homeowner had reset it a number of times before calling in an electrician.
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
mbrooke
Batteries Included
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- United States
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- Technician
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
rj,That an OCPD is designed to absorb a spike is a given we all accept.
The duration of the spike is what is intriguing here....
Disposals assume nuisance trips from lower settings , yet ground faults of just the right impedance may hum the flight of the bumblebee.
I think most here have been witness to this , in fact i've even had customers place their phones near panels ,resetting their 'vocal breakers' for my listening pleasure
This is not a short duration event, not 2,3,5,7 seconds, doesn't quite seem proprietary to any one make/model either. One would think enough magnetic flux builds up for the handle rating to mitigate it within this time ?
Having been under the impression the thermal qualities were slow , the mag trip fast ,is apparently not quite right then?
So i'm imagining all those circuits, components ,devices, lamp cords ,wire nuts , egc's, etc designed for 15 amps suffering the ill effects of this.....?
Some of this is starting to sink in....>
Vs.>
modified mag trip
~RJ~
What you are missing is that "magnetic flux" does not build up over time. It reaches a maximum once in each half cycle and goes back through zero again.
The magnetic force has to be large enough to overcome spring resistance and then the trip will happen, just like a snap switch going over center.
For practical purposes (not considering mechanical inertia) there is no time element involved in the trip other than the length of time if takes the contacts to open once the trip is committed.
P.S. I usually consider a spike to be a reference to a sub-cycle event rather than a motor starting surge.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Obviously, the solution is to duct tape the breaker handle in the ON position so that it won't trip any more. I am surprised that none of you bright boys came up with it.I did not leave the breaker on long enough to find out. Generally speaking, when you hear a loud abnormal hum, that's a good sign that something is wrong and you should shut the breaker off.
mbrooke
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- United States
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- Technician
Can you explain this further? Are you saying only 1 half cycle of current can unlatch the mechanism? :dunce:
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- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Of sufficient magnitude, yes, that's why it is referred to as an "instantaneous trip".
The current doesn't have to physically force the power contacts open, that's done with spring force. All the trip unit does is move a pawl on a catch that is holding the mechanism closed against the spring force. It doesn't need to move much to release it, just a fraction of an inch. The way the inexpensive resi breakers work is that there is a horseshoe shaped current path that all current needs to take. High current flow causes magnetic fields in those components to repel each other (look up "Ampère's force law" to understand this). If the current rises slowly, the components can absorb the mechanical force and spread it out so that it doesn't trip, giving the thermal element time to react. But a fast rise of that current makes it so that the mechanical force increases rapidly with no time for dissipation and it moves the pawl off the catch. From that point on, it's just the time it takes for the contacts to separate enough for the dielectric needed for the available voltage to stop current from flowing as the arc is quenched.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Yes, for the magnetic trip.
I can "trip" a snap switch by pushing steadily harder and harder until it finally actuates, or I can apply a slightly larger force suddenly by bouncing something off the switch handle.
There is a certain amount of motion required to move the handle of a snap switch from the rest position to the tripped position. The internal mechanism of a mag breaker is designed to minimize the corresponding distance.
Jraef explains it in much more detail.
mbrooke
Batteries Included
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- United States
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- Technician
So I only need a half cycle spike to open the breaker? Must this spike be sinusoidal?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
No, and if the maximum amplitude is high enough it also does not need to be a full 1/120th of a second.
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
:lol: :lol: i needed that Ggun....Obviously, the solution is to duct tape the breaker handle in the ON position so that it won't trip any more. I am surprised that none of you bright boys came up with it.
~RJ~
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Yes, and if you fail, you have to spend a year holding the breaker handle ON instead of using the duck tape... :angel:
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Illustrated version:
The red line indicates the power path. You can see where it makes a sharp "u-turn" at the top and comes back down to the load terminal. That's where the magnetic forces cause the device they call the "magnetic armature" to press against the release catch. If the current increases slowly, nothing happens there, but the bi-metal section slowly begins to deform and eventually moves the release catch. But if the current spikes fast, the armature can't spread out the force fast enough and moves it first.
The red line indicates the power path. You can see where it makes a sharp "u-turn" at the top and comes back down to the load terminal. That's where the magnetic forces cause the device they call the "magnetic armature" to press against the release catch. If the current increases slowly, nothing happens there, but the bi-metal section slowly begins to deform and eventually moves the release catch. But if the current spikes fast, the armature can't spread out the force fast enough and moves it first.
mbrooke
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So this all takes place in half a cycle, even less? I mean the armature being pulled in.
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