ECN Forum Forums General Topics of the Trade General Discussion Area I believe that fuses are far superior than circuit breakers!

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.