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Old 02-16-2015, 10:35 PM   #1
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Default Do new breakers trip faster?

Do new breakers (manufactured/installed in the last 10 years) short circuit trip faster than older ones?

In the last couple months, I have experienced a dead short on a 20A 120V circuit that barely made a spark. I was certain that it was a GFCI circuit because I saw no sign of arcing.

I used to be afraid to dead short a non GFCI circuit (to identify it ) because the arc freaked me out. In the old days, it was like a mini welder for a while until it tripped. Sometimes it would take more than one attempt.

I was just wondering if they changed the specs or design to recognize a short and trip faster.
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Old 02-16-2015, 10:49 PM   #2
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Most newer breakers do trip faster on a dead short, while older ones varied a lot. Square D single poles trip the fastest at 6 times the handle rating. This paper makes mention of magnetic trip curves:

http://paceforensic.com/pdfs/Circuit..._of_Safety.pdf
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Old 02-16-2015, 11:09 PM   #3
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As far as I know they are designed to trip during a fault in a time frame that is measured in "cycles per second". I suppose that over time the manufacturers could figure how to gain more speed in the mechanics of it all.
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Old 02-16-2015, 11:19 PM   #4
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It all depends on the short itself, high resistance ones are going to be slower to trip, bolted solid ones are going to go thru the bell shaped curve faster and trip it better. Also the fault current available at each location will be different, so that explains why the fireworks are different sometimes. In a busy office building a short circuit can boom an electrician right into the burn unit or grave, so they are not something to mess around with.
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Old 02-16-2015, 11:25 PM   #5
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Square D has always made fast reaction time as a selling point with their breakers (QO- Quick Open, Homeline uses the same mechanism)
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Old 02-17-2015, 01:25 AM   #6
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Quote:
Originally Posted by RIVETER View Post
As far as I know they are designed to trip during a fault in a time frame that is measured in "cycles per second". I suppose that over time the manufacturers could figure how to gain more speed in the mechanics of it all.
Hard to speed up the mechanics. That's why fuses are faster than circuit breakers on short circuit - nothing mechanical.

I agree that breakers are faster now. Maybe by design and maybe because old breakers are tired and slow.
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Old 02-17-2015, 03:23 AM   #7
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Quote:
Originally Posted by 99cents View Post
Hard to speed up the mechanics. That's why fuses are faster than circuit breakers on short circuit - nothing mechanical.

I agree that breakers are faster now. Maybe by design and maybe because old breakers are tired and slow.
A lot of it has to do with manufacturers lowering the magnetic trip value. Some older breakers were over 35 times the handle rating with others like FPE and Bulldog not even having magnetic trip. Unless you were next to the panel and the utility gave you a good amount of short circuit current older breakers took their time to clear a fault. With those breaker you could short something out at the end of a circuit and the lights in the whole house would dim for a second or two

Over the last 20 years manufactures have settled at about 10x the rating.

Also a small contribution to the above is unlatching time and arc extinguishing time, which as a whole can add a cycle or two in clearing the fault.
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Old 02-17-2015, 07:34 AM   #8
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I've seen some serious FPE lightning bolts....

But now i'm curious, because i suspect the potential are older subpanel(s) fed via a Square D , or other magnetically lower main tripping before the branch circuits do....

~CS~
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Old 02-17-2015, 08:01 AM   #9
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As far as I know the standard for breakers does not even require that the breaker have an instantaneous trip function. That being said, as far as I know all of the breakers do have that function, but the trip settings for the instantaneous trip vary over a wide range...from about 6x to about 25x as I recall.
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Old 02-17-2015, 08:02 AM   #10
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And we are talkin' ground faults, not shorts right? I've found a good short to brighten up most jobs rather quickly....~CS~
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Old 02-17-2015, 08:11 AM   #11
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Quote:
Originally Posted by don_resqcapt19 View Post
As far as I know the standard for breakers does not even require that the breaker have an instantaneous trip function. That being said, as far as I know all of the breakers do have that function, but the trip settings for the instantaneous trip vary over a wide range...from about 6x to about 25x as I recall.
I'm told all molded case breakers used in resi are inverse time vs larger E frames /bolt in instantaneous .

That said , how much of a trip disparity can be expected, and under what conditions?

~CS~
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Old 02-17-2015, 08:13 AM   #12
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Quote:
Originally Posted by 220/221 View Post

I used to be afraid to dead short a non GFCI circuit (to identify it ) because the arc freaked me out. In the old days, it was like a mini welder for a while until it tripped. Sometimes it would take more than one attempt.
I watched a guy turn a 6" long conductor (in a metal box) into a 2" long conductor before I got him to quit trying to trip the breaker by flashing the conductor to the box. Circa 1975 in a remodel job in downtown Norfolk. This was the same guy that did not understand you could not put two hot conductors from the same phase (different breakers) with the same neutral.
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Old 02-17-2015, 08:16 AM   #13
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Hopefully he gained some smarts since then Lou.....~CS~
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Old 02-17-2015, 08:26 AM   #14
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My Knipex circuit breaker tester still works after cutting through live cable - once with a fresh Siemens panel and once with a fresh QO panel.
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Old 02-17-2015, 11:39 AM   #15
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Quote:
Originally Posted by meadow View Post
Most newer breakers do trip faster on a dead short, while older ones varied a lot. Square D single poles trip the fastest at 6 times the handle rating. This paper makes mention of magnetic trip curves:

http://paceforensic.com/pdfs/Circuit..._of_Safety.pdf
Even though it's over thirty years old, it's an excellent article meadow, thanks for sharing.

For me, it drives home the myths in those days and the misconceptions blindly followed by experienced professionals.

Also a very strong hint as to the development of AFCI protection. I think I will change my mind and support AFCI protection throughout the home.

Once again, I digress. Sorry.

Borgi

Last edited by 51360; 02-17-2015 at 11:44 AM. Reason: Clarity addition
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Old 02-17-2015, 02:37 PM   #16
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Quote:
Originally Posted by chicken steve View Post
I'm told all molded case breakers used in resi are inverse time vs larger E frames /bolt in instantaneous .

That said , how much of a trip disparity can be expected, and under what conditions?

~CS~
The only breakers that can be instantaneous only are the ones that are part of a listed combination motor starter.

I believe that all most all of the common breakers are thermal magnetic. The thermal part provides the inverse time function and the magnetic part provides the intantaneous function.

The trip will be based on the breaker trip curves and the actual current flow.
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Old 02-17-2015, 03:52 PM   #17
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Quote:
Originally Posted by Borgi View Post
Even though it's over thirty years old, it's an excellent article meadow, thanks for sharing.

For me, it drives home the myths in those days and the misconceptions blindly followed by experienced professionals.

Also a very strong hint as to the development of AFCI protection. I think I will change my mind and support AFCI protection throughout the home.

Once again, I digress. Sorry.

Borgi


Welcome!

Keep in mind that lowering the magnetic trip and GFP will do exactly what an AFCI will do.


















Quote:
Originally Posted by don_resqcapt19 View Post
The only breakers that can be instantaneous only are the ones that are part of a listed combination motor starter.

I believe that all most all of the common breakers are thermal magnetic. The thermal part provides the inverse time function and the magnetic part provides the intantaneous function.

The trip will be based on the breaker trip curves and the actual current flow.
Instantaneous trip only breakers (at least from NEC rules) are used for fire pumps and critical process situations.

You are correct, UL does not require magnetic trip, though most breakers do have it simply because of manufactures adding it into the breakers.
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Old 02-17-2015, 04:33 PM   #18
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Quote:
Originally Posted by 220/221 View Post
Do new breakers (manufactured/installed in the last 10 years) short circuit trip faster than older ones?

In the last couple months, I have experienced a dead short on a 20A 120V circuit that barely made a spark. I was certain that it was a GFCI circuit because I saw no sign of arcing.

I used to be afraid to dead short a non GFCI circuit (to identify it ) because the arc freaked me out. In the old days, it was like a mini welder for a while until it tripped. Sometimes it would take more than one attempt.

I was just wondering if they changed the specs or design to recognize a short and trip faster.


Not sure , but in the early 80's I have seen a coworker burn 18 inches of 12 awg wire to get a 20A I-Line breaker , to Trip !



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Old 02-17-2015, 06:28 PM   #19
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Interesting topic.
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