Circuit Breaker verses Fuses
- Thread starter dercon
- Start date
- Status
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: Circuit Breaker verses Fuses
240.20(B)(1) is where you find the requirement for circuit breakers.
As you said, it's physically impossible to guarantee, so putting it into code for fuses would be ineffective.
240.20(B)(1) is where you find the requirement for circuit breakers.
As you said, it's physically impossible to guarantee, so putting it into code for fuses would be ineffective.
- Location
- Massachusetts
Re: Circuit Breaker verses Fuses
Many times circuit breakers are not required to open all poles when they 'trip'.
A typical 240 volt dryer breaker is not required to be common trip, only handle ties are required.
Handle ties only insure both poles are manual operated simultaneously but one pole can trip without effecting the other pole.
Are they?
Many times circuit breakers are not required to open all poles when they 'trip'.
A typical 240 volt dryer breaker is not required to be common trip, only handle ties are required.
Handle ties only insure both poles are manual operated simultaneously but one pole can trip without effecting the other pole.
peter d
Senior Member
- Location
- New England
Re: Circuit Breaker verses Fuses
Good point Bob. Multiwire circuits are a prime example of this.
Good point Bob. Multiwire circuits are a prime example of this.
peter d
Senior Member
- Location
- New England
Re: Circuit Breaker verses Fuses
Oh, if the question is cicuit breakers vs. fuses, I'll take fuses.
Oh, if the question is cicuit breakers vs. fuses, I'll take fuses.
Ed MacLaren
Senior Member
Re: Circuit Breaker verses Fuses
Both have advantages and disadvantages. Fuses are a "fail-safe" device. A defective breaker trip unit can only be detected by testing.
I wish there was some way we could educate the real estate and insurance folks about this.
Many of them think that fuses are obsolete.
Ed
Me too!
Both have advantages and disadvantages. Fuses are a "fail-safe" device. A defective breaker trip unit can only be detected by testing.
I wish there was some way we could educate the real estate and insurance folks about this.
Many of them think that fuses are obsolete.
Ed
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
Re: Circuit Breaker verses Fuses
The problem with fuses is twofold.
1. It is relatively difficult to change out a fuse compared to resetting a CB.
2. It is considerably easier to short out a blown fuse than a tripped breaker.
The problem with fuses is twofold.
1. It is relatively difficult to change out a fuse compared to resetting a CB.
2. It is considerably easier to short out a blown fuse than a tripped breaker.
Re: Circuit Breaker verses Fuses
How do you test a fuse to assure that it will function and is it within specs? Are fuses calibrated and checked before they are shipped? Or is it assumed by a matter of manufacturing statistics that the fuse you install will protect as the literature says. If a fuse blows can you check the fuse to assure that it didn't blow before it was designed to?
Sort of dumb questions but does this mean that we place a lot of trust in fuses that they will work as designed when it is difficult at best to verify that they will.
Do we assume that fuses are never defective?
Then what about breakers?
How do you test a fuse to assure that it will function and is it within specs? Are fuses calibrated and checked before they are shipped? Or is it assumed by a matter of manufacturing statistics that the fuse you install will protect as the literature says. If a fuse blows can you check the fuse to assure that it didn't blow before it was designed to?
Sort of dumb questions but does this mean that we place a lot of trust in fuses that they will work as designed when it is difficult at best to verify that they will.
Do we assume that fuses are never defective?
Then what about breakers?
B
bthielen
Guest
Re: Circuit Breaker verses Fuses
I wonder if the insurance companies look at it from a different perspective, right or wrong. I would agree that fuses are the safer bet but in the hands of the incompetent (not a negative term) DIY homeowner, circuit breakers are a safer bet.
My home is a prime example. When I bought it I discovered that nearly all of the 15A fuses had been replaced with 30A fuses. Probably because they were blowing them quite often since the home only had a 60A service supplying the system which had grown to include electric dryer, water heater, well pump, and range. Incidentally, the main disconnect fuses were also replaced with 100A rated. Fortunately, the wires went overhead in open air. With circuit breakers, this same homeowner would probably just reset them rather than be forced to replace them, which makes it easy to upsize and eliminate the nuisance tripping. For an inexperienced homeowner, replacing a fuse is much less intimidating and easier than replacing a circuit breaker. It is amazing the house hadn't burned down long ago.
Bob
I wonder if the insurance companies look at it from a different perspective, right or wrong. I would agree that fuses are the safer bet but in the hands of the incompetent (not a negative term) DIY homeowner, circuit breakers are a safer bet.
My home is a prime example. When I bought it I discovered that nearly all of the 15A fuses had been replaced with 30A fuses. Probably because they were blowing them quite often since the home only had a 60A service supplying the system which had grown to include electric dryer, water heater, well pump, and range. Incidentally, the main disconnect fuses were also replaced with 100A rated. Fortunately, the wires went overhead in open air. With circuit breakers, this same homeowner would probably just reset them rather than be forced to replace them, which makes it easy to upsize and eliminate the nuisance tripping. For an inexperienced homeowner, replacing a fuse is much less intimidating and easier than replacing a circuit breaker. It is amazing the house hadn't burned down long ago.
Bob
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Circuit Breaker verses Fuses
One thing to note, and I am not leaning one way or the other because all factors need to be considered.
Most standard (time-delay) fuses perform much worse than most new (since the mid 80's) circuit breakers for overcurrents in the 1.2 to 2x range.
For example average melt/tripping times, 120V, 30A load on a 15A OCPD:
Bussmann FRN-R15 - about 90 secs
Bussmann S15 - about 40 secs
Square D QO115 - trip time 7-25 secs
One thing to note, and I am not leaning one way or the other because all factors need to be considered.
Most standard (time-delay) fuses perform much worse than most new (since the mid 80's) circuit breakers for overcurrents in the 1.2 to 2x range.
For example average melt/tripping times, 120V, 30A load on a 15A OCPD:
Bussmann FRN-R15 - about 90 secs
Bussmann S15 - about 40 secs
Square D QO115 - trip time 7-25 secs
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Circuit Breaker verses Fuses
One thing to note, and I am not leaning one way or the other because all factors need to be considered.
Most standard (time-delay) fuses perform much worse than most new (since the mid 80's) circuit breakers for overcurrents in the 1.2 to 2x range.
For example average melt/tripping times, 120V, 30A load on a 15A OCPD:
Bussmann FRN-R15 - about 90 secs
Bussmann S15 - about 40 secs
Square D QO115 - about 7 to 25 secs
One thing to note, and I am not leaning one way or the other because all factors need to be considered.
Most standard (time-delay) fuses perform much worse than most new (since the mid 80's) circuit breakers for overcurrents in the 1.2 to 2x range.
For example average melt/tripping times, 120V, 30A load on a 15A OCPD:
Bussmann FRN-R15 - about 90 secs
Bussmann S15 - about 40 secs
Square D QO115 - about 7 to 25 secs
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Circuit Breaker verses Fuses
One thing to note, and I am not leaning one way or the other because all factors need to be considered.
Most standard (time-delay) fuses perform much worse than most new (since the mid 80's) circuit breakers for overcurrents in the 1.2 to 2x range.
For example average melt/tripping times, 120V, 30A load on a 15A OCPD:
Bussmann FRN-R15 - about 90 secs
Bussmann S15 - about 40 secs
Square D QO115 - about 7 to 25 secs
One thing to note, and I am not leaning one way or the other because all factors need to be considered.
Most standard (time-delay) fuses perform much worse than most new (since the mid 80's) circuit breakers for overcurrents in the 1.2 to 2x range.
For example average melt/tripping times, 120V, 30A load on a 15A OCPD:
Bussmann FRN-R15 - about 90 secs
Bussmann S15 - about 40 secs
Square D QO115 - about 7 to 25 secs
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Circuit Breaker verses Fuses
One thing to note, and I am not leaning one way or the other because all factors need to be considered.
Most standard (time-delay) fuses perform much worse than most new (since the mid 80's) circuit breakers for overcurrents in the 1.2 to 2x range.
For example average melt/tripping times, 120V, 30A load on a 15A OCPD:
Bussmann FRN-R15 - about 90 secs
Bussmann S15 - about 40 secs
Square D QO115 - about 7 to 25 secs
One thing to note, and I am not leaning one way or the other because all factors need to be considered.
Most standard (time-delay) fuses perform much worse than most new (since the mid 80's) circuit breakers for overcurrents in the 1.2 to 2x range.
For example average melt/tripping times, 120V, 30A load on a 15A OCPD:
Bussmann FRN-R15 - about 90 secs
Bussmann S15 - about 40 secs
Square D QO115 - about 7 to 25 secs
bphgravity
Senior Member
- Location
- Florida
Re: Circuit Breaker verses Fuses
The only problem I have seen with fuses is the greater potential of single-phasing 3 phase equipment. Unless you install phase monitoring devices, you may not know a phase is lost until the equipment burns up.
The only problem I have seen with fuses is the greater potential of single-phasing 3 phase equipment. Unless you install phase monitoring devices, you may not know a phase is lost until the equipment burns up.
bphgravity
Senior Member
- Location
- Florida
Re: Circuit Breaker verses Fuses
The only problem I have seen with fuses is the greater potential of single-phasing 3 phase equipment. Unless you install phase monitoring devices, you may not know a phase is lost until the equipment burns up..
[ February 25, 2005, 04:01 PM: Message edited by: bphgravity ]
The only problem I have seen with fuses is the greater potential of single-phasing 3 phase equipment. Unless you install phase monitoring devices, you may not know a phase is lost until the equipment burns up..
[ February 25, 2005, 04:01 PM: Message edited by: bphgravity ]
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Circuit Breaker verses Fuses
Most fuses offer worse protection than circuit breakers (at least those since the mid 80's) for overloads in the under 2x area.
For a 30A load on a 120V, 15A OCPD:
Bussmann FRN-R15 class R fuse - about 90 secs average melt time
Bussmann S-15 plug fuse - about 40 secs
Square D QO115 breaker - 7-25secs
Most fuses offer worse protection than circuit breakers (at least those since the mid 80's) for overloads in the under 2x area.
For a 30A load on a 120V, 15A OCPD:
Bussmann FRN-R15 class R fuse - about 90 secs average melt time
Bussmann S-15 plug fuse - about 40 secs
Square D QO115 breaker - 7-25secs
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Circuit Breaker verses Fuses
Bryan, if the fuse is sized correctly it will offer protection from single phasing. When a motor single phases it draws more current on the other legs. Also IEC overloads have better protection from single phasing than NEMA.
Bryan, if the fuse is sized correctly it will offer protection from single phasing. When a motor single phases it draws more current on the other legs. Also IEC overloads have better protection from single phasing than NEMA.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Circuit Breaker verses Fuses
sorry, duplicate post
[ February 27, 2005, 10:46 AM: Message edited by: jim dungar ]
sorry, duplicate post
[ February 27, 2005, 10:46 AM: Message edited by: jim dungar ]
- Location
- Massachusetts
Re: Circuit Breaker verses Fuses
A 3 phase motor supplied from a 4-wire, 3-phase system is not required to have a 'common trip' breaker.
All that is required is a handle tie, 240.20(B)(3)
That is still a design issue even with breakers.
A 3 phase motor supplied from a 4-wire, 3-phase system is not required to have a 'common trip' breaker.
All that is required is a handle tie, 240.20(B)(3)
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