I was using a chop saw in the shop Wednesday and the next day It trips the 20 amp breaker. The saw data tag shows 20 amps so I'm guessing I need a dedicated circuit?
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Do circuit breakers go bad?
- Thread starter 930dreamer
- Start date
bczygan
Well-known member
Re: Do circuits breaker go bad?
They do go bad, but you may also have an inrush current doing it. Different breakers are more sensitive.
Bill
They do go bad, but you may also have an inrush current doing it. Different breakers are more sensitive.
Bill
2Big2Ride
Well-known member
Re: Do circuits breaker go bad?
I had to get a 20A High Magnetic (HM) circuit breaker to run my old(er) table saw. More on the inrush here: https://www.garagejournal.com/forum/showthread.php?t=233513
I had to get a 20A High Magnetic (HM) circuit breaker to run my old(er) table saw. More on the inrush here: https://www.garagejournal.com/forum/showthread.php?t=233513
brokenknee
Well-known member
Re: Do circuits breaker go bad?
Yep, have a metal chop saw that would not work on a Homeline panel, 20 amp circuit. I changed the breaker and still the same problem, had to add a 30 amp circuit.
Moved and had a Siemens panel 20 amp circuit and had no problem with tripping the breaker.
Yep, have a metal chop saw that would not work on a Homeline panel, 20 amp circuit. I changed the breaker and still the same problem, had to add a 30 amp circuit.
Moved and had a Siemens panel 20 amp circuit and had no problem with tripping the breaker.
Re: Do circuits breaker go bad?
Our 100 amp main breaker in our old house failed while we were on a 2 week motorcycle trip. Came home to a 4' puddle of blood from our upright freezer.
Talked to a electrician on the job the next day back and he said breaker was probably heating up. Sure enough, when I got home, main breaker was very hot to the touch. I put a fan on it until I could buy a new one next day and swap it out.
Had to pull the meter of course, but it fixed the problem.
Our 100 amp main breaker in our old house failed while we were on a 2 week motorcycle trip. Came home to a 4' puddle of blood from our upright freezer.
Talked to a electrician on the job the next day back and he said breaker was probably heating up. Sure enough, when I got home, main breaker was very hot to the touch. I put a fan on it until I could buy a new one next day and swap it out.
Had to pull the meter of course, but it fixed the problem.
like2wheel
Well-known member
Re: Do circuits breaker go bad?
Yikes, you motorcycle guys are *********.. How many bodies did you have in that freezer?
Yikes, you motorcycle guys are *********.. How many bodies did you have in that freezer?
OP
Stay away from that house. 
Mr_fixit
Well-known member
Yes, but it could also be that the tool draws more power the older it gets.
wyliesdiesels
Well-known member
Try using an extension cord.
Theres another thread on here about this exact issue.
Theres another thread on here about this exact issue.
OP
Originally I was using an extension cord= worked fine, next day same setup didn't work. Plugged in at the receptacle= no workie.
Richard Cranium
Well-known member
I have seen them that wouldn't stay on, or they wouldn't reset.
sberry
Banned
The mechanism also ratchets up from hi current starts. Once it resets it may be fine. I was welding from one a while back. Went to use a grinder and itv tripped. Reset it, never had a problem again.
Had a 2 pole fail about 10 yrs ago. It just quit .
Had a 2 pole fail about 10 yrs ago. It just quit .
wyliesdiesels
Well-known member
What brand of breakers do you have 930dreamer?
OP
I'm thinking Square D?
Aceman
Well-known member
Like mentioned above, look for a "high magnetic" breaker.
Chop saws tripping regular breakers is a very common problem.
Chop saws tripping regular breakers is a very common problem.
sberry
Banned
Yes, mine tripped a 20 and it's so close to the panel which doesn't really help. My helper ran another circuit, since we had 10 he used that. If I would have caught it would have been 12 but it goes to the one outlet. Used a 30, the cord on the saw is 14. Not saying this is exactly the way it should be done,,, disclaimer,, but it works. The saw will go north toward 40A if a guy leans on it, can't recall it ever tripping during a cut but would trip 20 every 3 or 4 starts. Has never sprung the 30.
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alfredeneuman
Well-known member
Where did you hear THAT ??
jeepinerdeep
Well-known member
Go Bad- Yep I have lost about 3 Square D QO breakers in the last 10 yrs. ( New 1972 ) One 60a and a couple small ones. Failure mode more swift and there was no reset even out of the panel.
On the other hand I had a Dewalt abrasive saw that I never could get to work on a 20a circuit. Inrush was just too high, I didn't like the saw so I never researched it. Sold it.
On the other hand I had a Dewalt abrasive saw that I never could get to work on a 20a circuit. Inrush was just too high, I didn't like the saw so I never researched it. Sold it.
OP
Breaker is a GE.
sberry
Banned
It was something I recalled from acseminar I took some 30 plus years ago. Seems, the best i can recall was this was the reason they often didn't trip on the first cycle but after 3 or so.
I certainly could be wrong, it was a long time ago and I was probably drunk when I was there and a lot of it was over my head anyway, still is.
As I mentioned earlier, I was using a Maxstar on a 20 and 1/8 lohy . I finished the rod which is really a size too big for that circuit. Few minutes later plugged in a common 4 1/2 grinder, as soon as I tick the switch it snapped the breaker. In decades,,, never tripped a breaker from one of those.
I certainly could be wrong, it was a long time ago and I was probably drunk when I was there and a lot of it was over my head anyway, still is.
As I mentioned earlier, I was using a Maxstar on a 20 and 1/8 lohy . I finished the rod which is really a size too big for that circuit. Few minutes later plugged in a common 4 1/2 grinder, as soon as I tick the switch it snapped the breaker. In decades,,, never tripped a breaker from one of those.
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alfredeneuman
Well-known member
The instantaneous aka magnetic trip mechanism is basically just a solenoid
Some of them have adjustable trips, but only in larger industrial breakers
Some of them have adjustable trips, but only in larger industrial breakers
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sberry
Banned
It seems they often work several cycles after a reset and then a tick sets them off, reset, work again the same way. Maybe they warm up, but the last time i had it happen with the little grinder it had sat several minutes and the previous weld was only a rod or so as best i recall.
Yes, even though I don't work with it I am aware some bigger ones are adjustable. As I sais, it was a long time ago and don't recall the exact context. Seems it was a Schneider guy .
Yes, even though I don't work with it I am aware some bigger ones are adjustable. As I sais, it was a long time ago and don't recall the exact context. Seems it was a Schneider guy .
American Locomotive
Well-known member
Circuit breakers have two components; they have a thermal time delay trip and an instantaneous magnetic trip.
The instantaneous magnetic trip is usually 10-15x the breakers rated current - so in some cases it could take 300A to instantly trip a 20A breaker. The magnetic trip is also extremely fast responding - as little as 1/2 an AC cycle (0.0083 seconds).
The thermal trip on the other hand can take anywhere from 2-3 hours to trip at very slight overloads, to as fast as 0.5 seconds at overloads approaching 6-8x the breakers rated current. As heat builds in the breaker, the thermal trip will kick in faster and faster with subsequent overloads. They sell breakers with all kinds of different trip curves for different applications.
I suspect big angle grinders, miter saws, etc.. can sometimes instantly trip breakers if the commutator stops in just the right location where it's nearly a dead short across the motor leads. They also sell special breakers with a higher than normal magnetic trip threshold just for these occasions.
The instantaneous magnetic trip is usually 10-15x the breakers rated current - so in some cases it could take 300A to instantly trip a 20A breaker. The magnetic trip is also extremely fast responding - as little as 1/2 an AC cycle (0.0083 seconds).
The thermal trip on the other hand can take anywhere from 2-3 hours to trip at very slight overloads, to as fast as 0.5 seconds at overloads approaching 6-8x the breakers rated current. As heat builds in the breaker, the thermal trip will kick in faster and faster with subsequent overloads. They sell breakers with all kinds of different trip curves for different applications.
I suspect big angle grinders, miter saws, etc.. can sometimes instantly trip breakers if the commutator stops in just the right location where it's nearly a dead short across the motor leads. They also sell special breakers with a higher than normal magnetic trip threshold just for these occasions.
The extension cord acts like a resistor/inductor and limits the inrush current. Removing the e-cord and the inrush seen by the breaker goes up, causing the trip.
lg
no neat sig line
nelstomlinson
Well-known member
American Locomotive nailed it. Breakers are intended to carry a steady load of up to 80% of their rated capacity, and so a 20A breaker will eventually trip due to heat with a steady load over 16A.
If you want to pull a steady 20A, you need a 20A/0.8=25A breaker. Then there is the inrush current, which is another problem.
If you want to pull a steady 20A, you need a 20A/0.8=25A breaker. Then there is the inrush current, which is another problem.
sberry
Banned
It wont trip at 16 on thermal, its a 20. Its rated to full load for 3 hours which is continuous.
vtsoundman
Well-known member
This is incorrect.
Breakers will supply 100% of their rating just about indefinitely. My experience in the lab testing various breakers for PQ gear also substantiates this conclusion - in fact, only 'good breakers' would trip @ 110% of rating in an hour or so.
Per the NEC, the max continuous load (>3 hrs ) cannot be more than 80% of the branch circuit OPD. This is why toasters and blow dryers can pull 1800W on a 15A circuit -> these are not considered continuous loads.
Borrowing this from here
Here's the trip curve for a 20 ampere Square-D QO circuit breaker.
The vertical axis is time in seconds, and the horizontal axis is multiples of current. I've highlighted in orange what two times the breakers rating looks like (40 amperes). As you can see, even at 40 amperes this breaker shouldn't trip for about 9 to 35 seconds. This is because it's relying on the thermal protection, and the bi-metal strip has to heat enough before it pulls the circuit open.
I've also highlighted in red what it would take to trip the breaker in one second, since an observer might consider a second "instantaneous". You'll notice that it should take between 4.5 and 8 times the breakers rating, before the breaker trips in under a second. That means your saw would be pulling 90-160 amperes, when the breaker tripped.
If your saw is pulling that much current, the problem is not the breaker, it's the saw. Increasing the size of the breaker is not the solution.
Check the saw for faults, including a short-circuit. You may also want to test/replace the breaker, as breakers can go bad.
Op, if you are plugging this saw into several locations, then the extension cord method is probably the only practical solution. Running the saw on a dedicated 20a ckt is necessary for more headroom during startup and running under load. If there are other loads running on this ckt at the same time, keep them off or move them. Since this ckt/receptacle(s) are general convenience, there are no NEC exceptions for ocp upsizing. You will need to replace with another 20A cb.
If you have a particular ckt that you are always plugging into, I would change that CB to a 20 amp high magnetic (HM) version. Verify if GE# THQL1120HM is compatible with your panel. Using this will eliminate the temptation to otherwise increase the OCP value improperly when using a standard delay cb in the magnetic region.
I can’t locate the trip curves specifically for GE THQL…HM, but in similar fashion, the magnetic trip curve for a standard SQ D QO 1P 20A is 6.0X – 11.0X rated current while the SQ D QOHM 1P 20A is 11.0X – 42.0X rated current.
Several mfrs. make these in the 15/20a single pole rating for residential/light commercial use. They’re just not a mainstream item and apparently not that well known. Shop the internet for pricing.
The link below shows the difference of a std trip curve vs. that of a HM style. Compare the blue color region to the green/yellow colors in the magnetic range. This is the operating region used in the cb while starting the saw. The green/yellow region gives more time to get up to speed w/o cb tripping. The thermal region quickly reverts back to the standard protection values of the blue curve. This is the region where “long-term” overloaded ckts get their protection from.
https://www.bing.com/images/search?...08008242809340737&selectedIndex=60&ajaxhist=0
If you have a particular ckt that you are always plugging into, I would change that CB to a 20 amp high magnetic (HM) version. Verify if GE# THQL1120HM is compatible with your panel. Using this will eliminate the temptation to otherwise increase the OCP value improperly when using a standard delay cb in the magnetic region.
I can’t locate the trip curves specifically for GE THQL…HM, but in similar fashion, the magnetic trip curve for a standard SQ D QO 1P 20A is 6.0X – 11.0X rated current while the SQ D QOHM 1P 20A is 11.0X – 42.0X rated current.
Several mfrs. make these in the 15/20a single pole rating for residential/light commercial use. They’re just not a mainstream item and apparently not that well known. Shop the internet for pricing.
The link below shows the difference of a std trip curve vs. that of a HM style. Compare the blue color region to the green/yellow colors in the magnetic range. This is the operating region used in the cb while starting the saw. The green/yellow region gives more time to get up to speed w/o cb tripping. The thermal region quickly reverts back to the standard protection values of the blue curve. This is the region where “long-term” overloaded ckts get their protection from.
https://www.bing.com/images/search?...08008242809340737&selectedIndex=60&ajaxhist=0
nelstomlinson
Well-known member
Can't argue with the trip curve. Looks as if you're right.
This is probably where I got my incorrect impression. I knew we designed for 80% of rated capacity for some reason.
Edited to add: but also see the info at this square-D link: https://blog.schneider-electric.com...g-confusion-80-vs-100-rated-circuit-breakers/
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Fixin'Stuff
Well-known member
Do circuit breakers go bad? Yes, but not very often. My last house had all of the 240 volt circuit breakers in a box on the side of the house. In Central Texas. On the WEST side of the house. One 60-amp breaker fed all of the 120 volt circuits, housed in a panel inside the garage at the other end of the house. One summer the breaker feeding the 120 volt circuits tripped off in the afternoon. 105-110 degrees, with the breaker box in direct sunlight. It had worked fine for 20+ years. I reset the breaker and all was well for a few days, then it tripped again. Yep, late afternoon, hot day, direct sun on the box.
Amprobe showed the house was only pulling 21 amps on one leg and 17 on the other, so nowhere even close to the 60 amp rating of the breaker. A trip to Home Depot and $9 later, I had a new breaker. Installed it and it never tripped again. I suspect that a spring had grown weak in the thermal-trip part of the old breaker and the heat of the afternoon sun was tripping it.
If you're interested in seeing how a modern breaker operates, there's a slow motion video of the internals of one here:
Amprobe showed the house was only pulling 21 amps on one leg and 17 on the other, so nowhere even close to the 60 amp rating of the breaker. A trip to Home Depot and $9 later, I had a new breaker. Installed it and it never tripped again. I suspect that a spring had grown weak in the thermal-trip part of the old breaker and the heat of the afternoon sun was tripping it.
If you're interested in seeing how a modern breaker operates, there's a slow motion video of the internals of one here:
slow
Well-known member
cool video, growing up I had a clear sample QO breaker, it was neat to see how it worked.
checkthisout
Well-known member
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- Sep 5, 2008
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In my personal experience I have found that they go bad if they are repeatedly tripped due to overload.
The bi-metal portion eventually deforms to the point that the breaker trips well under it's rated capacity.
Same thing happens if the breaker overheats due to a loose connection at the breaker. The heat generated damages the bi-metal strip. Same result.
The bi-metal portion eventually deforms to the point that the breaker trips well under it's rated capacity.
Same thing happens if the breaker overheats due to a loose connection at the breaker. The heat generated damages the bi-metal strip. Same result.
sberry
Banned
I just fooled with the meters today. 140 Maxstar and a 140 Linc wire feeder with 023. Could get them to pull 22 welding, adding 35 ft of 14 cord causes 6 to 8 v drop but very little change in current draw. About 3 or 4 volts on 50 ft of 12 cord added. Almost 100A on the feeder and with 22 in 92 out with 3/32 lo hi which was nice and toasty. I could turn it up to 98 and it took in 25, this is on a 20/120v. Didn't trip breaker.
As an operator couldn't tell the difference with the cords. Adding 50 ft of 14 is really minor, it's not why some machine worked or didnt. 50 ft 12 none. This class of machine could tolerate 100 ft of 12 without a problem.
As an operator couldn't tell the difference with the cords. Adding 50 ft of 14 is really minor, it's not why some machine worked or didnt. 50 ft 12 none. This class of machine could tolerate 100 ft of 12 without a problem.
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