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05-07-2010, 03:31 PM
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#16
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Member
Join Date: Jul 2008
Location: Canada (s/w ON.)
Posts: 2,294
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Testing a breaker
Quote:
Originally Posted by trosenda
Hi,
I have a 20 amp square D home line circuit breaker that trips very intermittently, seemingly without any excess load. The circuit serves 6 outlets with one computer that draws ~300 watts and 160 watts of lighting.
The breaker is 6 months old but I can't think of other issues in the circuit so I would like to know if this is the problem. I could just change it and hope for the best but because it trips so rarely I won't know for weeks if the problem is solved. Is there a way to test the functionality of said breaker?
Thanks,
Thomas
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A 20 amp breaker should carry a 2400 watt load! If I wished to test this I would plug in portable heater(s), noting the wattage rating of each unit.
Any electrical device will work, such as a toaster, toaster oven, a microwave or even hair dryers.
A computer would be a poor choice as its load may not be constant.
Once the total wattage of all the devices exceeds 2400 watts the breaker should trip!
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05-07-2010, 03:57 PM
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#17
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Licensed electrician
Join Date: Sep 2007
Location: Maryland
Posts: 5,984
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Testing a breaker
Depending on the amount of overload the breaker will carry more than it is rated for. For example a 20 amp breaker does not trip at 20.05 amps.
__________________
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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05-07-2010, 04:04 PM
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#18
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Tool Geek
Join Date: Jun 2008
Location: Pacific Palisades CA
Posts: 2,444
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Testing a breaker
Quote:
Originally Posted by trosenda
I have a 20 amp square D home line circuit breaker
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Thomas, I just realized that the C/B you describe comes in two flavors.
Which one is yours?
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05-07-2010, 11:34 PM
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#19
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Inspector/Instructor
Join Date: Dec 2009
Location: NC
Posts: 369
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Testing a breaker
Quote:
Originally Posted by PaliBob
A contractor that does a lot of work in industry may have a C/B tester.
I am in possession of a 25 year old C/B Tester made by EIL, but while I think they are now out of business, there are other sources.
The one I have was used by my old contractor boss when I filled in as a Temp. The reason I have it now is that since he retired, he wants me to put it on E-Bay for him.
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COOL! Would love to have this. Probably cant afford though. Its Neat! 
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05-08-2010, 03:26 PM
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#20
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Member
Join Date: Jul 2008
Location: Canada (s/w ON.)
Posts: 2,294
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Testing a breaker
Quote:
Originally Posted by Jim Port
Depending on the amount of overload the breaker will carry more than it is rated for. For example a 20 amp breaker does not trip at 20.05 amps.
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Hmmm! Now I'm curious! At what point does it trip? 20.10 amps?
There must be some variables, such as ambient temperatures etc!
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05-08-2010, 03:35 PM
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#21
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It was a dark and stormy
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,954
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Testing a breaker
Quote:
Originally Posted by PaliBob
Thomas, I just realized that the C/B you describe comes in two flavors.
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If the OP has the GF option I think you found the cause!
http://www.google.com/search?hl=en&s...=&oq=&gs_rfai=
Quote:
Originally Posted by Wildie
Hmmm! Now I'm curious! At what point does it trip? 20.10 amps?
There must be some variables, such as ambient temperatures etc!
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If you find a trip curve, it shows the limits.
These limits probably mean that 95% or 99% of the breakers sold fall within those limits.
BTW, Hosfelt 'former PN#56-192, puts out 3A at 12V, so probably 12A into a short circuit. It's $10.
20 ea. of these would give you an awful lot of current at a safe voltage.
DIY at its best!
Last edited by Yoyizit; 05-08-2010 at 03:49 PM.
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05-08-2010, 03:43 PM
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#22
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Sparkaholic
Join Date: May 2010
Location: Miami, Florida
Posts: 184
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Testing a breaker
Could also be arcfault breaker
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05-09-2010, 06:33 AM
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#23
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Tool Geek
Join Date: Jun 2008
Location: Pacific Palisades CA
Posts: 2,444
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Testing a breaker
Homeline Breakers come in a lot of flavors but I think the OP most likely has the ground-fault one pole 20A or the Arc Fault breaker.
Thomas, What variety of C/B do you have?
.
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05-10-2010, 10:35 AM
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#24
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Member
Join Date: Oct 2009
Location: Missouri
Posts: 37
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Testing a breaker
Just a regular Square D home line 20 amp breaker ie. Not a GF or AF breaker. If it had been a GF or AF breaker I would have been looking for those problems in loads on the circuit.
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05-10-2010, 11:17 AM
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#25
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It was a dark and stormy
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,954
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Testing a breaker
Quote:
Originally Posted by trosenda
Just a regular Square D home line 20 amp breaker ie. Not a GF or AF breaker. If it had been a GF or AF breaker I would have been looking for those problems in loads on the circuit.
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You could make a circuit that waits as long as necessary and indicates an overcurrent if one exists the next time the breaker trips. It would be a very simple Event Recorder.
But if the breaker trips and no overcurrent event is captured, I don't know what to say. 
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05-13-2010, 04:23 PM
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#26
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Member
Join Date: Oct 2009
Location: Missouri
Posts: 37
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Testing a breaker
Hi,
So it tripped again last night in the middle of the night. That's the 3rd time in three weeks. So.. today I switched the breaker for another and I bought a clamp mater to test the circuit power draw. With everything on: lights, and computer it draws 6.3 amps. However when the laser printer warms up or prints there is a peak draw of 23 amps  . (That's me - surprised) .
I don't actually think that was the problem because the printer should not be doing anything at night nor does the circuit trip with that peak current draw when I'm working here during the day. but... the printer is a recent acquisition and I did not have the problem pre-printer.
If the new breaker doesn't solve it I will move the printer to another circuit and see what gives.
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05-13-2010, 08:23 PM
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#27
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It was a dark and stormy
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,954
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Testing a breaker
Quote:
Originally Posted by trosenda
there is a peak draw of 23 amps . (That's me - surprised) . |
The RMS current draw may be lower. These things seem to draw pulses of current several times per second. When mine printed the lights flickered.
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05-13-2010, 08:39 PM
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#28
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Xtreme DIY'r
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
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Testing a breaker
Quote:
Originally Posted by trosenda
However when the laser printer warms up or prints there is a peak draw of 23 amps . (That's me - surprised) |
What happened to not much draw on this circuit 
Laser printer changes everything
Every place I have worked larger laser printers are on a dedicated circiut
Is the laser printer left on at nite ?
It will keep the fusing element hot & will draw power
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05-13-2010, 10:11 PM
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#29
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Member
Join Date: Oct 2009
Location: Missouri
Posts: 37
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Testing a breaker
The printer is like the $150 best buy laser printer nothing large or fancy. It still seems weird that it should be the cause of the occasional circuit trips even if it is cycling through some sort of warm up at night because nothing else is on at that time and it doesn't do it during the day.
The clamp meter claims to calculate true root mean square
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05-14-2010, 01:54 AM
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#30
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" Euro " electrician
Join Date: Apr 2006
Location: WI & France { in France for now }
Posts: 4,965
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Testing a breaker
Quote:
Originally Posted by trosenda
The printer is like the $150 best buy laser printer nothing large or fancy. It still seems weird that it should be the cause of the occasional circuit trips even if it is cycling through some sort of warm up at night because nothing else is on at that time and it doesn't do it during the day.
The clamp meter claims to calculate true root mean square
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What model and brand name the clamp on amp meter it is ?
Due some are not really worth a hoot.
Merci,Marc
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