Fuse or Breaker
- Thread starter Woodyz
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ron
Senior Member
- Location
- New York, 40.7514,-73.9925
The biggest benifit of breakers are easy to reset after investigation. Fuses often are replaced by whatever happens to be around.
Can you test a fuse to see if it will work properly by responding to a fault or an overload?
If one fuse blows in a 2 or 3ph system what prevents single phasing? In a 240v 1ph 3w system if you blow a fuse in one line the remaining line will back feed threw a 240v load energizing the supposed de-energized circuit.
Regarding as to how a fuse responds to a over load, as I understand it an element has to melt. If it almost melts but doesn?t because the overload goes away will the fuse respond to an overload change? Of course fuses can provide a higher KAIC than circuit breakers if rated to do so.
Blow a fuse? Hope there is a spare. And fuses aren't cheep to replace.
Isn't it nice to have a breaker that clears all lines when one line calls for a trip and is able to be reset and closed without searching for a replacement breaker?
And, yes, if in doubt a breaker can be tested to assure its integrity.
If one fuse blows in a 2 or 3ph system what prevents single phasing? In a 240v 1ph 3w system if you blow a fuse in one line the remaining line will back feed threw a 240v load energizing the supposed de-energized circuit.
Regarding as to how a fuse responds to a over load, as I understand it an element has to melt. If it almost melts but doesn?t because the overload goes away will the fuse respond to an overload change? Of course fuses can provide a higher KAIC than circuit breakers if rated to do so.
Blow a fuse? Hope there is a spare. And fuses aren't cheep to replace.
Isn't it nice to have a breaker that clears all lines when one line calls for a trip and is able to be reset and closed without searching for a replacement breaker?
And, yes, if in doubt a breaker can be tested to assure its integrity.
- Location
- Bremerton, Washington
In my experience fuses nearly always offer better motor protection than a circuit breaker or MCP. If you size the fuse slightly above motor FLA, that will protect against single phasing, and the IEC overloads offer good protection from single phasing
When I install fuses I always provide spares.
When I install fuses I always provide spares.
davidr43229
Senior Member
- Location
- Columbus, Oh
A fuse offers many advantages over a Circuit Breaker as stated above, with higher AIC ratings and sized correctly prevents damage to the motor (Type ll Protection).
In addition is also provides better Arc Flash Protection with faster interruption of a Shortcircuit (fault) and can be better Selectively Coordinated to meet several of the 2005 NEC standards.
OSHA within 1910.334 states it is illegle to just reset a Circuitbreaker.
The "Job" of any Overcurrent Protection Device ( fuse or breaker) is to sit there indefinately until something else happends within that Electrical distribution system
Just my $.02
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
I agree that by following the fuse manufacturer sizing recommendations you can achieve great selectivity. However, when performing arc flash calculations, I have many many situations where a breaker will offer lower arc flash energy let through simply because of the time-current characteristics at the calculated fault/arcfault current.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
davidr43229 said:
This is true only if the fault current is large enough to cause the fuse to enter its current limiting range. In Bussmann's SPD they show that at 4kSCA a 400 LPS-RK1 fuse still has an arc flash incident energy (AFIE)level of >20cal/cm^2. I just finished an arc flash study where the clearing time of one installed LPS-RK1 fuse was >1.6 seconds because the branch circuit arc fault was only about 7x the fuse size. I have seen several situations where a KRP-C1200 fuse had to be exchanged with a KLU in order to lower the AFIE
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
ron said:
Ron,
I agree, but what happens to the selective system when one fuse is replaced with a different style or a different manufacture. How times have you opened a branch circuit disconnect switch to see three different fuses install? It seems that the fuses that are most likely to blow (and therefore most likely to need selectivity) are the ones most likely to be replaced with "whatever is on the shelf".
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
The choice seems to be driven by one of two things.
Money - fuses are often less money.
Production - people who are concerned about losing a few minutes of production often want breakers because they don't have to hunt to for a replacement fuse that may not be easy to come by, especially at 2:00 am.
Money - fuses are often less money.
Production - people who are concerned about losing a few minutes of production often want breakers because they don't have to hunt to for a replacement fuse that may not be easy to come by, especially at 2:00 am.
brian john
Senior Member
- Location
- Leesburg, VA
NOT BY PROFESSIONALS. A person that will install any fuse that is handy will replace a 20 amp CB with a 30 amp CB. You can't stop stupid acts.
We test circuit breakers, so I like to see them installed (more work) but I prefer fuses.
jim dungar said:
Jim,
With ANY overcurrent protective device there can be a range of available fault currents where the device may not operate quickly. What about a breaker with STD settings adjusted to hold of a fault for 6 cycles. This is why Arc-Flash studies are key to determining the level of danger, because there are so many factors associated. The bottom line is that when examined for speed of operation there is no comparison between a fuse and a circuit breaker, the fuses will open the circuit in less time under most circumstances, which will result in lower flash energies.
davidr43229
Senior Member
- Location
- Columbus, Oh
I am total agreement with this above quote.
In as far as
I can tell you that companies such as Goodyear, Honda, Ametek, Longenburger,PPG, Dupont, Playtex, Colgate, The Limited, Nationwide, Ohio State University and Delphi are all companies that have a trained Maintainence department, with Fuse stock, Circuitbreakers stock, Contactors, Motors, Switches, Berings, Belts, Solvents always in stock for most outtages. If the act of 1 single maintenance person would mirror the actions above, they wouldn't be working there much longer.
Just my $.02
I?ve always found this topic to provoke a lively discussion.
As a breaker man with bolted faults fuses it would agree would respond better to limit fault current. All that energy going into a bolted fault works to the fuse?s advantage in clearing the fault. A breaker can't use that and advantageously because it uses the speed at which the contacts open and the arc chutes ability to cool and dissipate the arc.
However, what are the statistics of bolted fault Vs arcing faults? Aren?t arcing faults more likely to occur and they can cause some big time damage if not cleared quickly. As an arcing fault escalates does the current feeding into the arc get greater or does it decrease?
With arcing faults? You really can't define the magnitude of an arcing fault because each arcing fault can initiate in a different way and the current feeding into the fault changes. A breaker may see the arcing fault in it's magnetic trip element and open immediately where a fuse element may take time to melt if the arc doesn't clear itself giving the fuse enough time to react. But who really knows as each incident will certainty be different and there will be no givens.
As far as motor protection? There is a misconception of fuses and MCPs protection motors because they don't. Thus the combination motor starter which consists of a contactor to start and stop the motor. The overload relay when is sized to protect the motor if it is overloaded by sensing the current it is drawing preventing motor damage by over heating, etc. And the fuses or MCP (magnetic only breakers) which protect the motor circuit and take the circuit off line should there be a failure in that circuit. This usually means that there has been an insulation break down in the motor itself and there most likely is an arcing fault to ground within the motor. Art 430.52 refers to ground fault protection which is what it's all about.
Again, arcing faults often start small and escalate. Remember that the motor is failing so you are not really protecting th3e motor but limiting damage an preventing a fire. With all confidence I believe that a properly applied and set MCP can be more closely coordinated to respond sooner to a motor which is failing. You aren't going to be able to do that with fuses. The arcing fault must be of great enough magnitude and be sustained for a long enough period of time for a fuse to react and clear. Again, is this true all of the time? Probably not, because the dynamics of every arcing fault is going to be different. I would like to think that you would believe that an arcing fault to ground in a motor would start out small, and a MCP with its instantaneous trip would most likely clear a low-level arc quicker.
In any event, unlike fuses, if an MCP trips it clears all phases and not just one, as such, single phase protection is not require unless it is required for other reasons.
As a breaker man with bolted faults fuses it would agree would respond better to limit fault current. All that energy going into a bolted fault works to the fuse?s advantage in clearing the fault. A breaker can't use that and advantageously because it uses the speed at which the contacts open and the arc chutes ability to cool and dissipate the arc.
However, what are the statistics of bolted fault Vs arcing faults? Aren?t arcing faults more likely to occur and they can cause some big time damage if not cleared quickly. As an arcing fault escalates does the current feeding into the arc get greater or does it decrease?
With arcing faults? You really can't define the magnitude of an arcing fault because each arcing fault can initiate in a different way and the current feeding into the fault changes. A breaker may see the arcing fault in it's magnetic trip element and open immediately where a fuse element may take time to melt if the arc doesn't clear itself giving the fuse enough time to react. But who really knows as each incident will certainty be different and there will be no givens.
As far as motor protection? There is a misconception of fuses and MCPs protection motors because they don't. Thus the combination motor starter which consists of a contactor to start and stop the motor. The overload relay when is sized to protect the motor if it is overloaded by sensing the current it is drawing preventing motor damage by over heating, etc. And the fuses or MCP (magnetic only breakers) which protect the motor circuit and take the circuit off line should there be a failure in that circuit. This usually means that there has been an insulation break down in the motor itself and there most likely is an arcing fault to ground within the motor. Art 430.52 refers to ground fault protection which is what it's all about.
Again, arcing faults often start small and escalate. Remember that the motor is failing so you are not really protecting th3e motor but limiting damage an preventing a fire. With all confidence I believe that a properly applied and set MCP can be more closely coordinated to respond sooner to a motor which is failing. You aren't going to be able to do that with fuses. The arcing fault must be of great enough magnitude and be sustained for a long enough period of time for a fuse to react and clear. Again, is this true all of the time? Probably not, because the dynamics of every arcing fault is going to be different. I would like to think that you would believe that an arcing fault to ground in a motor would start out small, and a MCP with its instantaneous trip would most likely clear a low-level arc quicker.
In any event, unlike fuses, if an MCP trips it clears all phases and not just one, as such, single phase protection is not require unless it is required for other reasons.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
MO_EE said:
I don't believe there is sufficient independent documentation to prove this statement for most branch circuits, especially those below 100A using UL489 molded case circuit breakers at typical branch circuit arcing fault levels. I was just stating what I have observed from performing arc flash studies using commercial software packages. and, i do recognize there are differences betwqeen the performance of main, feeder, and branch protective devices.
brian john
Senior Member
- Location
- Leesburg, VA
I am no engineer but from what I have read (and expierenced) I agree with you....BUT David, I saw your statement coming from a mile away. I just expecte the "ABOVE" statement to be from you.
This is one of those topics that, in the end, most have to agree to disagree.
I prefer fuses in the industrial world I live in, supplemented with an adequate spares package. CB's are used sparingly, mostly in specific customer-specified locations. I've seen customers abuse both. Replacing fuses with larger rated fuses. Constantly resetting CB's. Removing a trip unit and replacing it with a higher rating. Replacing a din-mount CB with a larger unit. All while not bothering to troubleshoot why the problem happened in the first place.
Bottom line IMHO is there is plenty of room for both to be used, and to be abused.
I prefer fuses in the industrial world I live in, supplemented with an adequate spares package. CB's are used sparingly, mostly in specific customer-specified locations. I've seen customers abuse both. Replacing fuses with larger rated fuses. Constantly resetting CB's. Removing a trip unit and replacing it with a higher rating. Replacing a din-mount CB with a larger unit. All while not bothering to troubleshoot why the problem happened in the first place.
Bottom line IMHO is there is plenty of room for both to be used, and to be abused.
davidr43229
Senior Member
- Location
- Columbus, Oh
Brian John,
Nah...... I wanted others to chime in as well, but I did smile alot reading it!
I don't believe that there is sufficient independant documentation to dis-prove the statement either!
kc8dxx,
Just my $.02
Nah...... I wanted others to chime in as well, but I did smile alot reading it!
Jim,
I don't believe that there is sufficient independant documentation to dis-prove the statement either!
kc8dxx,
Amen brother.
Just my $.02
brian john
Senior Member
- Location
- Leesburg, VA
I was wondering if you were off line or just not paying attention.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
David,
It' just that I am against any statement that says (or implies) any one type protective ALWAYS provides lower arc flash incident energy than a different type. It is very easy to find examples that contradict any "absolute" statement concerning overcurrent protective devices.
It' just that I am against any statement that says (or implies) any one type protective ALWAYS provides lower arc flash incident energy than a different type. It is very easy to find examples that contradict any "absolute" statement concerning overcurrent protective devices.
- Location
- Massachusetts
jim dungar said:
Especially if the statement that 'fuses are better' comes from a fuse manufacturer engineer.
It's always good to consider the source of the information.
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