breakers II
- Thread starter wyatt
- Start date
- Status
- Location
- Massachusetts
Re: breakers II
Tony that sounds about right.
Kind of surprising isn't it.
Tony that sounds about right.
Kind of surprising isn't it.
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: breakers II
Ever notice how good breakers hold on construction jobs ? I have had temp lights maxing out breakers and hold all day.Romex would get down right hot and still hold
Ever notice how good breakers hold on construction jobs ? I have had temp lights maxing out breakers and hold all day.Romex would get down right hot and still hold
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: breakers II
Ever notice that the breaker has 40? C on it? That's the ambient temperature that the breaker is listed and tested at, from what I understand.
Yeah, it's a thermomagnetic breaker. Both temperature and the EMF of the circuit act to trip the circuit.
Ever notice that the breaker has 40? C on it? That's the ambient temperature that the breaker is listed and tested at, from what I understand.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: breakers II
No fuses are not necessarily better. The last time I did a comparison of tripping times, a 30A breaker trip faster than a 30A fuse would melt on a 15% overload.
From Square D's product FAQ website:
Question: What is the ambient operating temperature of a circuit breaker?
Answer: Circuit breakers are calibrated for use at 40 degree C. They should be re-rated if used at temperatures below 25 degrees C or above 40 degrees C.
No fuses are not necessarily better. The last time I did a comparison of tripping times, a 30A breaker trip faster than a 30A fuse would melt on a 15% overload.
From Square D's product FAQ website:
Question: What is the ambient operating temperature of a circuit breaker?
Answer: Circuit breakers are calibrated for use at 40 degree C. They should be re-rated if used at temperatures below 25 degrees C or above 40 degrees C.
Re: breakers II
"better" depends a whole lot on the application.
I believe you will find the fuse advantage comes primarily from the the fault current limiting
characteristics. This comes more in play with "short circuits" than overloads.
"better" depends a whole lot on the application.
I believe you will find the fuse advantage comes primarily from the the fault current limiting
characteristics. This comes more in play with "short circuits" than overloads.
Re: breakers II
Augie,
I agree. But then to address "short circuits" one can break them down to types of "faults," arcing faults and bolted faults. Then go one step farther and considered the percentages of occurrence of each type. Protection is directed towards bolted fault which I believe make up a very small percentage of faults. I wish I could lay my hands on the document but arcing faults make up the vast majority as I remember.
But it's sure nice not to go looking for a fuse but to simple reset, latch, and close a breaker.
And when one considers a 40degC breaker in a panel located in a basement which may be 20degC protecting cable in an attic which may be 50degC you do have to wonder how this protection works when there are so many variables.
One realizes that it is important to size the cable correctly, and maybe conservatively, derating it when necessary.
Augie,
I agree. But then to address "short circuits" one can break them down to types of "faults," arcing faults and bolted faults. Then go one step farther and considered the percentages of occurrence of each type. Protection is directed towards bolted fault which I believe make up a very small percentage of faults. I wish I could lay my hands on the document but arcing faults make up the vast majority as I remember.
But it's sure nice not to go looking for a fuse but to simple reset, latch, and close a breaker.
And when one considers a 40degC breaker in a panel located in a basement which may be 20degC protecting cable in an attic which may be 50degC you do have to wonder how this protection works when there are so many variables.
One realizes that it is important to size the cable correctly, and maybe conservatively, derating it when necessary.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: breakers II
If you look at these GE breakers, you will see that, depending on manufacturers tolerance (width of characteristic), at approximately 1 x the trip (marked on breaker), it will trip at 1000 seconds. It may permit an overload of as much as 1.4 x the trip for 1000 seconds, if the manufacturing coincides. You can also see the adjustment required when operating at different ambient temperatures.
We've had many 20A molded case breakers tested (primary injection tested), and most will trip at the values equal to or less than the left hand side of the tolerance band (on curve).
http://www.geindustrial.com/publibrary/FCS.jsp?id=38652.30055.13376.4767&format=PDF&file=GES-6201.pdf
If you look at these GE breakers, you will see that, depending on manufacturers tolerance (width of characteristic), at approximately 1 x the trip (marked on breaker), it will trip at 1000 seconds. It may permit an overload of as much as 1.4 x the trip for 1000 seconds, if the manufacturing coincides. You can also see the adjustment required when operating at different ambient temperatures.
We've had many 20A molded case breakers tested (primary injection tested), and most will trip at the values equal to or less than the left hand side of the tolerance band (on curve).
http://www.geindustrial.com/publibrary/FCS.jsp?id=38652.30055.13376.4767&format=PDF&file=GES-6201.pdf
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