My personal opinion follows:

I believe that fuses are far superior for protection against an overcurrent condition. Some types of circuit breakers fail and we have been made aware that they have a history that may not be the safest protection.

Terms Defined:

Overcurrent.

Any current in excess of the rated current of equipment or the ampacity of a conductor.

It may result from overload, short circuit, or ground fault.

FPN: A current in excess of rating may be accommodated by certain equipment and conductors for a given set of conditions. Therefore the rules for overcurrent protection are specific for particular situations.

Assume for discussion sake that you are 100% correct; i.e., that a fuse provides a "superior" level of overcurrent protection.

Which is more likely to present a safety hazard?

- a circuit breaker that fails to trip, vs.
- an uninformed homeowner who replaces a blown 15 amp fuse with a 20 or 30 amp fuse "because it was all I had and it got the lights back on"?



[This message has been edited by rlrct (edited 05-12-2004).]

Joe,
Are you serious, or trying to stir up some conversation?
Single phasing of equipment and replacement during emergency is the main reasons not to use fuses.

I agree with Joe. I never saw a fuse that did not blow on overcurrent or short/fault. If we all moved back to fuses, they could be designed so only the correct rating of fuse is installed for the conductor being protected. Toward the end there of the use of fuses that was being done with those screw in devices (I don't remember what they were called )that reduced the size of the socket so that only the correct sized fuse could be installed.

rlrct wrote:

If you're referring to a circuit breaker that fails to trip into the point of meltdown.. I think I'd rather have the 30A fuses... while I certainly understand 30A fuses on 14 or 12awg wire for general applications is a hazard.. At least theres some limit.. in a dead short situation, a 30A fuse would blow, whereas a frozen breaker, so to speak, wouldn't.. Besides, homeowners are getting pretty handy at changing breakers out over here when they think they're "too small"

-Randy
PS...Gene,... You referrig to the type "S" adapters?

-Randy

Use Type S Fuses!!

The fuse was first and still is, and CB's are not always reliable, especially the older ones!

FACT: The fuse will always Open or "B L O W"

rlrct: To prevent the misapplication of plug-type fuses often used in older style residential fuse panels, NFPA 73 - Inspection Code for Existing Dwellings, in 2.3.5 - "where evidence of overfusing of or tampering with Edison-based-type fuses exists, Type S nontamperable adapters and fuses shall be installed". Thus, provided the fuse panel was properly inspected, this misapplication can be avoided.

I think Mean Gene's comment really gets to the heart of the issue, that is that a fuse can provide reliable overcurrent protection over the life of the system. A circuit breaker can do this as well provided it is properly maintained and tested (and replaced when needed) in accordance with manufacturer's instructions, NFPA 70B and NEMA AB4. However, many installations do not do so much as simply "exercising" the circuit breakers periodically. Because the circuit breaker is a mechanical device this and other maintenance/testing procedures are periodically needed to assure proper operation and protection. Thus, often the only time we know a circuit breaker needs maintenance or replacement is after the problem occurred.

With respect to Ron's comment, single phasing is not a fuse/breaker issue because neither device will protect against all single phasing conditions - it is really only an issue for multi-phase motor loads and with that, the only thing that will protect against all conditions is a single-phase relay (with come with most new electronic overload relays). With regard to replacement of fuses. If the fuse opened due to a short-circuit, you have much bigger problems than simply replacing the fuse (you need to fix the short-ciruit first). Because fuses require replacement (and cannot be reset), that may actually be a benefit (and avoid a potential OSHA violation). In addition, if this is referring to mains and feeders in a system, it most likely was a short-circuit so automatic resetting should be avoided until verified to be an overload or fixing of the short-circuit. Thus, often resettability is only beneficial in branch circuits because most overcurrent conditions here are overloads.

Great, now just where it that I can get a few copies of AFCI fuses? Oh, BTW, I would also like to get some adjustable blow fuses and some common blow fuses for some industrial work.

I agree that the ‘S’ type fuses would effectively eliminate over-fused circuits.

One advantage of CB’s is the flexibility in constructing a breaker panel. Would you have a “snap-in” fuse holder similar to a CB such that circuits could be added by installing the appropriate fuse-holder in a panel’s empty slot? I suppose that if there were no such thing as a “half-size fuse holder”, that would tend to limit panel overcrowding.

With fuses as the primary OCP, how would you handle GFCI and/or Arc Fault protection?

While single-phasing may be a motor-related problem, what about 2-pole common trip OCP for 240vac appliances (ex. dryer)?

Gee!! Another fault?
http://www.joetedesco.com/blowup.jpg

Think this fellow was feeling a bit uncomfortable, or just getting ready to go home because his machines won't work?

I believe, that most engineers feel that fuses are better too, and electricians are very happy when fuses are specified!



[This message has been edited by Joe Tedesco (edited 05-12-2004).]

My comments regarding single phasing, was the instance when only one (or two) of three fuses (three phase) will blow.
Most older engineers also don't trust those fancy multifunction MV relays (ie Multilin) or fancy smancy PLC's, and still require electromechanical relays. Some are set in their ways.

Is there any reason (other than _cost_) not to simply put a fuse in series with a circuit breaker, coordinated so that the circuit breaker will trip in normal circumstances, but the fuse will blow if the breaker fails?

-Jon

I like breakers. I find them to be reliable.

removing a breaker is easier than removing a fuse when working on circuits.

Rather than stepping backwards, why don't we improve the standards for circuit breakers? There are some circuit breakers currently on the market that we know are prone to fail (GE, Siemens, Cutler Hammer BR series, Square D Homeline) and others we know do a very good job (Square D QO and Cutler Hammer CH series). The lower quality ones need to have the standards boosted.

I had a job with a Cutler Hammer CH 200 amp main disco and Siemens 200 sub panel. A 20 amp circuit had a dead short on it that would trip the 200 amp main, but not the 20 amp Siemens breaker. Makes you wonder what good the Siemens breakers are doing.

I'm with CharlieE, where's the AFCI and GFCI fuses? From someone who has been a champion of the AFCI, the fuse statement in Joe's initial post suprises me a little. Does the undeniable superiority of the fuse in an over-current situation outweigh the AFCI's bennefits? Or the GFCI's? In my own opinion, fuses are superior to circuit breakers in some applications and inferior in others. Unless all aspects of an application are factored in I don't think you can make a blanket statement such as "always use circuit breakers" or "always use fuses".

I used to prefer breakers.

Then I got a job as the electrician for a maintenance dept.

If a breaker trips, someone might reset it dozens of times before they let me know. And it could be dozens of different people.

When a fuse blows they come to me because I keep them in my shop. If they come back a second time, they do not get a second fuse untill I check it out.

Another thing, we have a few situations where if theres a short the 20 amp branch AND the 3000 amp main trip. Never had a main breaker trip when a branch fuse blew yet.

There are of course problems with fuses such as the no blow pipe type.

Joe,
A long time ago, ( I think you heard this story before ) I had a problem with one of my customers. It seemed after a thunder and ligtning storm the customer complained that they didn't have any power in their house. I went out and saw a 200 amp single phase service. There were 2 200 amp main service fuses and the rest of the panel had 40 Zinsco circuit breakers. All of the breakers tripped but the 2 main 20 amp fuses were good. I checked around, and reset all of the breakers and everthing worked OK. About a month or two later the same thing happened. This time it was a nice sunny dry day. The fuses were OK but all 40 circuit breakers tripped. I couldn't find anything. I knew the head lineman at the power company (POCO) and I asked him the check his transformer on the pole. ( Which was at the bottom of the driveway of my customer.) The POCO said that everything was OK. I think that after several months and a lot of phone calls, the POCO changed the transformer and everything was OK after that. My thoughts would be that there was a spike our surge that would trip the magnetic part of the circuit breaker but not affect the fuses.

Low-voltage molded-case circuit breakers have a tendency to “vent” during fault interruption—similarly rated fuses do not.

As for me, it all depends on the load characteristics and the Customer.

Fuses introduce the problems of Single Phasing when loads such as Motors and Transformers are conserned, but the problem may go beyond that.

Circuit Breakers may fail to open under excessive Fault conditions - like an improper AIR situation (installing a device with an AIC that is lower than what's available), or the device fails in the closed position.
Other Circuit breaker issues come from when they have been setup in a non-selective fashion - with either a "Fuse / Breaker Combination" or simply all OCPDs are Circuit Breakers.

Single Phasing issues may be brought on from a failed Breaker protecting a 20 Amp Branch Circuit (Fault on the Branch Circuit), and a Fused Main Switch with one-time / fast acting type Fuses. Seen it several times (troubleshoot calls).

As I said, it all depends on the installation. The decision to be made will reflect the hazards vs the consequences of each type OCPD.

Each type device has good and bad points. Each one has a "Better Place" in the design of the systems at a given project.
Each one has its own drawbacks from failure or worse - replacement by unqualified persons.

Incorrect fault ratings on either type will have bad effects.

For breakers, it's obvious about an excessive SCA through the device than it can handle...
"BANG!!!"..."SMOKE!!!"..."FLAMES!!!"

Same for a fuse with improper Arc quenching ability. Arc inside the fuse will be sustained until something finally gives.

Then again, the 3/4" All-Copper Fuse Replacements don't offer much help either!

No way to outguess the most determined idiots, as they just keep turning out bigger, better idiots!
(had to include the typical disclaimer!).

For a Fuse type Main, these could easily incorporate an extended protection device - like AFCI or GFCI. It would be setup like a GFPE protected main switch (480Y/277 VAc 3Ø 4W 1000 Amps or more).
There are both types - Circuit Breaker and Fuse types. The Fault sensing device trips a multipole switch (looks like a breaker - but has no overcurrent protection elements).

Scott35

a properly sized fuse is better then a fpe or Zinsco NO-Trip Breakers

When I am called to repair a "bad breaker", which is a wiring problem or overload and not the breaker 99% of the time, I'll usually find that there's been someone that's tried repeatedly to reset the breaker (often against a dead short). This many times does damage the breaker. Fuses won't allow this type of problem, and the trouble can be fixed without additional damage being done to the electrical system.

With regards to installations with >10K fault currents:
The high interrupting capacity of fuses makes them much more attractive ($$$$$) than the use of high interrupting capacity circuit breakers.

I like fuses better...S

Thanks Scott:

The voice and opinion of a respected master electrician and seasoned mechanic is always welcomed, in addition to those who responded here and have real world experiences!

Yoa!

Don't hold your breath too long for AFCI Fuses may be just around the corner!!

Probably will be far less that those in the marketplace at the present time!

This was from Mike Holt's newsletter this morning.

This post has certainly generated alot of good comments. I have represented both the circuit breaker and fuse manufacturers in my past. I think the important thing to take away is that both fuses and circuit breakers can provide proper protection if proper maintenance and (testing for circuit breakers) are performed. Any device can be misapplied or improperly maintained. In addition, a fuse or circuit breaker may be better suited for a specific application. However, in my opinion there are less "concerns" with fuses compared to circuit breakers over the life cycle of the device.

With regards to the future of circuit breakers and fuses, I think we will see much improved features and protection from both devices.

With regards to arc flash protection, Ryan J appears to have picked a situation where a cirucit breaker can provide better arc flash protection. One caution here, what is the device type and ampere size...there really isn't enough information in his post to determine the application. With arc flash protection the, fault current, arcing fault current, type and size of the device has a great impact. There can be cases where a circuit breaker can be shown to provide better protection than a fuse, however, in general, I would argue that a fuse will provide better protection in the majority of cases. Another consideration can be the reliablity of operation. With circuit breakers you are relying on an expected response time that can only be confirmed with proper maintenance and testing.

We do have systems that prevent from insertig a too high rated fuse into a socket, but allow to use smaller ones. it's done by the diameter of the "diazed" fuse's front contact. the thicker, the more amps.
the socket has an interchangable insert or ring with the diameter for the right current.

we also have diazed fuse sockets that have a drawer where the fuse lies in. just pull it out of the module, old fuse out, new fuse in, and push it back in. works *almost* as fast as breaker resetting, 3ph fuse change in ~ 5-10 seconds, but difficult in the dark

One problem I have with the debate of fuses versus breakers is the final installation.

Fuses are tested and listed as open air devices. For proper application they must be installed in fuse holders and require an associated disconnecting means. Most 240V fusible devices are only rated at 10KA fault levels regardless of the rating of the installed fuse.

I have also seen many fusible switches which have not been exercised and so were unable to be opened when needed.

Finally, my experience has been that miniature molded case breakers (designed and built since the late 70s) are faster than fuses at clearing the low level faults encountered in residential applications. Fuses are faster at the higher level faults found in industrial settings. In fact the speed that these breakers operate at is part of the fuse-breaker coordination difficulties and why Bussmann no longer supports the up-over-and-down method of calculating fault levels.

Anyone priced fuses lately? Sometimes when troubleshooting an intermittent problem I can go through a box of fuses in a day. Some are in the $20-30 apiece. Sure would be cheaper to just reset the circuit breaker.
We have, just a guess, over 100 different types and sizes of fuses on campus and trying to keep them all in stock is nearly impossible. We had had equipment down for days waiting for a fuse that no one stocks. I've only had one occasion that a breaker failed to trip. But, I have also had fuses get so hot they charred the cardboard and didn't blow.

We have such panels in Britain. In fact, in many ranges the same panel will accept either breakers or fuse carriers, so there's nothing to stop you fitting a mixture of both.

Fuses often have the edge on interrupt ratings, and under our wiring rules can be used to "protect" a C/B which would otherwise have too low an interrupt rating. For example, the typical domestic C/B is rated 6kA interrupt, which could be exceeded in many locations close to a sub-station, however the cartridge fuse used in the main service will have a much higher rating and will blow should a C/B be unable to break a dead-short condition.

Joe,
Please let me digress for a second.
I'm of the school of thought that says, that a CB is a fixed, Non adjustable Protection device.
Made to trip at it's design current.
Usually, these are not tampered with by the H/O.
Most come in Magnetic(short-circuit) and Thermal Protection (Over-current), usually in the same device.
Take your average fuse, it can be changed at will, for a higher current Fusing element, whatever that may be.
Your Forum is proof of that, mate!.

JBD, are we talking about the same thing??


An example would be a Safety Switch

You are correct but that is only when the Class R rejection fuse clips have been installed in the safety switch. There are many 30A devices that do not even have provisions for Class R fuses (especially pull out designs).

Also, the above mentioned favorite Type S plug fuses rated are only 10KA max.

It is not fair to "bash" all miniature breakers because of the old Zinsco and FPE problems. A comparable bashing of all fuses would be to look at the renewable link and standard plug fuse over sizing issues.

In reality, other than Zinsco and FPE, how many 50 year old breakers have been found to not trip? Yes, I know there are many that wouldn't reset but they still protected the conductors.

I remember something about an unofficial study some UL engineers did back in the early 80s. They went to their own houses and removed their load centers without disturbing the breakers. They then ran normal overcurrent tests on these breakers and found no appreciable loss of the original tripping characteristics.

And yes, I know there are different tripping characteristics between manufacturers and tripping elements, some breakers are "faster/better" than others. But I have never seen any factual indication that miniature breaker characteristics are inherently degraded by age.

Well I am EXTREMELY surprised to come across such a thread. On a DIY forum I would expect it, but not an one of this calibre.

Joe, with respect, how are you able to justify your comments, so far your arguments do not stand up to scrutiny. I am not sure about the internal workings of MCB's in the US, but in the UK their operational characteristics are far superior to any Fuse link.

In the UK we have three main types of MCB, Types B, C, and D.

Type B are designed to be used in Domestic and Commercial premises on circuits that do not have large inductive loads placed upon them, such as lighting and small power sockets. They have a momentary capacity of 3 to 5 times the rated current, but they will operate if a load exceeding 1.2 times their maximum potential loading occurs for more than 5 seconds.

Type C are designed for medium size Inductive and Capacitive loads, such as small motors and transformers etc up to about 7.5kVA, single (230V) or three phase (400V). The momentary capacity for Type C's are 5 to 10 times Full Load current. Like the B's they will only tolerate 1.2 times rated maximum for 5 seconds before operating.

Type D, also known in the trade as Motor rated, are designed for use on heavy Inductive and Capacitive loads, rated up to 125A single or three phase, they can protect some heavy duty kit. They will with stand bewteen 10 and 20 times full load for brief periods at startup.

If you need something rated above 125A, such as fire pumps for example, then these will be protected by the MCB on steroids, Moulded Case Circuit Breakers (MCCB) These are available from 63A single phase to 1850A three phase. These also have a higher switching and fault current capacity. Where as MCBs have a rupture capacity of 7.5kA or 10kA, depending on BS, the MCCB's have rupture capacities starting at 25kA. The biggest MCCB's (800A upwards) can have rupture capacities of up to 60kA.

To demonstrate this...



In case anyone is interested in the internals of the MCB's we use in the UK, here is something I knocked up for the AE3



[This message has been edited by FWL_Engineer (edited 05-16-2004).]

This information belongs in the forum that will have some interest in these products.

This equipment is not used here in the USA.

I still think fuses are better, thank you for reminding me about this discussion.

Most of the replies here are in support of my personal opinion.

I'm with Joe on this one. We've all seen breakers fail to open at one time or another where a fuse certainly would have blown.

...As cumbersome,and archaic as they are,I also concur with Joe regarding their reliability..The downside is...imagine a 42 circuit panel board filled with those things...Sheeesh!! At very least,a breaker design that would incorporate "fuse" technology wouldn't be a bad idea..There goes my Square"D" endorsement...
Russ

I think what this thread is saying is that circuit breakers in the US are lower quality than in the UK.

That is not to say fuses are not used, service cutouts contain large pattern HRC BS1361 Ceramic Fuses, and there are many applications were BS88-2 or BS88-6 Fast Blow or Slow blow Ceramics are used.

There are instances where the use of circuit breakers may not be a viable option for operational issues.

However I still believe that MCB's, RCBO's and RCD's are far superior to fuses in general situations. In 21 years in this job I can honestly say I have only ever come across a about a dozen knackered MCB's, and all the UK ones fail safe anyway..that can be a pain, but it's a way of finding out there is a problem.

Well, as interesting as another debate would be, I say both have their set-backs...the most obvious to me is the manufacturers gaurantee on the circuit breaker...they are all gauranteed to operate properly "1" time...after that , all bets are off...

On the other hand, fuses seem to beg to be over-sized by "handy men" all over the world !!!

So, what to do ?...put a lock on the panel and give the key to the closest "qualified personel"...as we all know, they never re-engineer anything !!!

Not sure how you arrive at that conclusion. Certainly they may have slightly different characteristics, but that doesn't make them inferior as you need to take the other ways in which an installation differs into account. You can't condemn every U.S. circuit breaker just because of Federal Pacific!

By the way, terms like RCD, RCBO etc. are not used in the U.S. and will probably confuse the issue here.

480 Kicks, (if I can be so informal)

Actually, UL listing requires all circuit breakers to undergo two trips at rated current then at fault levels. After these two series of trips nothing is guaranteed.

How many times have you gone into an older house that still has a functional fuse panel?
The fuse panels will and have lasted a long time. But almost every one I have seen for the last several years has lots of oversized fuses. Those 30 amp fuses don't blow so the HO does not have to got to the store and buy a new fuse. At least they can reset there own breakers and are not as likely to buy 30 amp single pole breakers. It's more work to replace the breaker than to reset it, but with a fuse you have to replace it any way.
With proper sizing IMHO circuit breakers are a better for houses and small commercial buildings.

House I am in now, 40 year old Federal Pacific fuse panel. Whole row of pullouts and 4 rows of the "idiot proof" fuses.

Dryer fuse would occasionally blow. 30 amp cartridge on 8 AWG wire. (dryer on the other extreme of the house).

Downstairs watching tv one evening and I hear a buzz coming from the panel. Little investigation and I find the dryer pullout too hot to touch and the buzz is the arc from the buss to the fuse.

I heartily agree that fuses being the once and done kind of machine, seem to more reliably open a circuit, as long as arc flash hazards are taken into acount. But the problem I have seen is that the infrastructure holding them in place might be at the end of it's service life.

The FP went in the trash and a Sq D homeline now lives in it's place.

TW

It kind of surprises me that so many of you are limiting this discussion to only houses, and beating the "Stablok/Zinsco dead horse" some more.

OK Scott I will get out of houses.

Many of our commercial customers specify fusible switch gear over breakers.

One of them has a strange policy of sizing the fusible switch one size larger than needed.

If we will be installing 40 amp fuses they ask for a 100 amp switch, 200 amp fuses would need a 400 amp position.

Every fuse we install in their gear has to get fuse reducers.


[This message has been edited by iwire (edited 05-20-2004).]

I think that this is a false debate. While the two products seem to address the same concern, there are clearly different circumstances that favor each.
CB's don't require the homeowner to find a hardware store open on Sunday night. Nor will one be tempted to go through a box of fuses while "troubleshooting." After a few trips, people tend to figure out that you don't run the microwave and air conditioner at the same time. With the installation of new CB services, homeowners are finally updating the grossly over-strung circuits that, in the past, they 'fixed' by over-fusing. Moreover, since it takes some time to trip, I can actually measure the current draw as I track down the problem.
Fuses do react faster- and for when things go real bad, fast is good. It's no accident, though, that fuses are typically used together with other overload devices. Even without other devices, fuses can often be sized closer to the desired level.
And, as others have posted, ther's more to 'safe' than fuses and CB's. GFCI's and TVSS have prooven their utility, and AFCI's may yet do the same.