Fuses vs breakers

[mbrooke]

From another site:

https://www.youtube.com/watch?v=3dckmSgp1nw&feature=youtu.be

 

[charlie b]

We don't allow "drop links." So either post some information on what that link will show, so that a person can decide whether they are interested in following it, or this thread will have to be removed.

 

[mbrooke]

We don't allow "drop links." So either post some information on what that link will show, so that a person can decide whether they are interested in following it, or this thread will have to be removed.

One of my first drop links (thinking the video will be self explanatory) after several thousand posts, only to be met with discontent. This is why I am loyal to electrician talk, we discuss the bigger picture rather than quibbling over what we know not to be the case.


Anyway, in terms of the video fuses seem to provide better protection over breakers on many levels in though the only down side being single phasing.

 

[Jraef]

...
Anyway, in terms of the video fuses seem to provide better protection over breakers on many levels in though the only down side being single phasing.

In a video designed and produced by a company that does NOT make circuit breakers? I could have foretold that outcome without watching it (in fact I didn't watch it all, but I've sat through the same crud with Bussman).

The skewed viewpoint is not necessarily invalid, but it does leave out several parts of the story that might have been helpful to the CB side of the argument. A couple of important ones:
1) If the fault is significantly BELOW the available fault current rating of the fuse, it may not clear in time, or even at all.
2) Typically videos like this gloss over the important issue of single phasing in a 3 phase system, meaning that if one fuse blows, the others do not always do so in enough time to prevent damage to 3 phase motor loads. Circuit breakers always open all 3 phases when there is an overload on one phase. Again, I didn't watch it all, too slow and boring. But like I said, I've seen the Bussman version of this story, it's shockingly similar.
3) I did watch the section wherein they pop a 25A breaker and after 8 short circuit trips, it resets but the contacts don't close. That's a spurious argument. NOBODY in their right mind would EVER close a breaker 8 times into a bolted fault!!!

Both technologies have their place, neither is perfect, neither is evil.

 

[jim dungar]

Anyway, in terms of the video fuses seem to provide better protection over breakers on many levels in though the only down side being single phasing.

Fuses and circuit breakers have both existed for almost 100 years.

If there was a clear 'best device' the marketplace would have weeded out the bad one decades ago.

 

[mbrooke]

Fuses and circuit breakers have both existed for almost 100 years.

If there was a clear 'best device' the marketplace would have weeded out the bad one decades ago.

But they way I see it one has a trade off to the other. Fuses coordinate better, are fail safe, and in terms of unqualified personnel there is no breaker to keep closing back into the fault. Breakers are convenient and provide automatic 3 phase breaking.

 

[mbrooke]

In a video designed and produced by a company that does NOT make circuit breakers? I could have foretold that outcome without watching it (in fact I didn't watch it all, but I've sat through the same crud with Bussman).

The skewed viewpoint is not necessarily invalid, but it does leave out several parts of the story that might have been helpful to the CB side of the argument. A couple of important ones:
1) If the fault is significantly BELOW the available fault current rating of the fuse, it may not clear in time, or even at all.
2) Typically videos like this gloss over the important issue of single phasing in a 3 phase system, meaning that if one fuse blows, the others do not always do so in enough time to prevent damage to 3 phase motor loads. Circuit breakers always open all 3 phases when there is an overload on one phase. Again, I didn't watch it all, too slow and boring. But like I said, I've seen the Bussman version of this story, it's shockingly similar.
3) I did watch the section wherein they pop a 25A breaker and after 8 short circuit trips, it resets but the contacts don't close. That's a spurious argument. NOBODY in their right mind would EVER close a breaker 8 times into a bolted fault!!!

Both technologies have their place, neither is perfect, neither is evil.

Trust me, Ive heard some stuff. :jawdrop:

 

[rt66electric]

Ive seen lots of breakers fail to trip

Ive seen lots of breakers fail to trip

Ive seen lots of breakers fail to trip. or burn up.,,, or such or don't forget the Z-co "never-trip" breakers.

I have never seen a fuse "fail to blow"

BUT>>>>>>


A breaker is much safer to reset. and easy to find in the dark



A litttle-ole-lady gets the surprise of her like when she screws in another fuse to a "bolted fault"

 

[mbrooke]

Ive seen lots of breakers fail to trip. or burn up.,,, or such or don't forget the Z-co "never-trip" breakers.

I have never seen a fuse "fail to blow"

BUT>>>>>>


A breaker is much safer to reset. and easy to find in the dark



A litttle-ole-lady gets the surprise of her like when she screws in another fuse to a "bolted fault"

I agree a breaker is much easier to reset, but that can create more of a hazard. Before any breaker is reclosed a mego ohm meter test along to an investigation into what caused the fuse to blow should be conducted. While the breaker in the video simply failed by not being able to conduct power, in the real world an explosion is a possible alternative.

 

[jim dungar]

But they way I see it one has a trade off to the other. Fuses coordinate better, are fail safe, and in terms of unqualified personnel there is no breaker to keep closing back into the fault. Breakers are convenient and provide automatic 3 phase breaking.

Fuses do not always coordinate better. It is relatively easy to get breakers that will coordinate on line to ground fault currents in the <100A range, it is extremely harder to do this with fuses.

Breakers are designed and tested to be closed onto a fault. The UL 489 test says the breaker must open on a fully rated fault, it must be reset then closed onto the same fault, it must safely interrupt the fault again, then it must be replaced.

An unqualified person that would repeatedly close a breaker into a fault, is probably just as likely to replace a blown fuse with whatever they can find, negating any coordination and engineered protection which may have existed. This is one reason that fusible equipment must use rejection style clips for faults currents in excess of 10kA.

According to some sources, 3-phase bolted faults account for less than 0.5% of all faults, while line to ground faults account for about 95% of them.

 

[mbrooke]

Fuses do not always coordinate better. It is relatively easy to get breakers that will coordinate on line to ground fault currents in the <100A range, it is extremely harder to do this with fuses.

But don't some fuses come with a coordination ratio like mentioned in the video?

Breakers are designed and tested to be closed onto a fault. The UL 489 test says the breaker must open on a fully rated fault, it must be reset then closed onto the same fault, it must safely interrupt the fault again, then it must be replaced.

That is true, but there is no way to know if those 2 tries have already been exceeded. I know electricians who will reclose breakers. And while its not right by any means, it does happen. Also, what I the breaker is 30 years old, exceeded its 2 tries and then gets subjected to a fault again?

An unqualified person that would repeatedly close a breaker into a fault, is probably just as likely to replace a blown fuse with whatever they can find, negating any coordination and engineered protection which may have existed. This is one reason that fusible equipment must use rejection style clips for faults currents in excess of 10kA.

I agree, you make a good point.

According to some sources, 3-phase bolted faults account for less than 0.5% of all faults, while line to ground faults account for about 95% of them.

That sounds about right. And this is where breakers win. In theory the 2 remaining fuses can back feed the fault making the danger greater.

 

[jim dungar]

But don't some fuses come with a coordination ratio like mentioned in the video?

The coordination ratio only works for those specific fuses, if you go to a different manufacturer (e.g. lower cost provider) the coordination is lost. electronic trip breakers can be coordinated between 100A and 125A, to my knowledge the best fuse ratio is 1.5X. And yes, electronic trip breakers are expensive.

That is true, but there is no way to know if those 2 tries have already been exceeded. I know electricians who will reclose breakers. And while its not right by any means, it does happen. Also, what I the breaker is 30 years old, exceeded its 2 tries and then gets subjected to a fault again?

The 2x limit is at the fully rated maximum 3-phase bolted fault current, which only occurs as part of a wiring error. A breaker can be reset hundreds of times for the more common 'overload' fault. The real problem is not knowing what happens in between these fault levels.

That sounds about right. And this is where breakers win. ...

Did you just say that for 95% of probable faults, breakers are better?

 

[Tony S]

 

[mbrooke]

The coordination ratio only works for those specific fuses, if you go to a different manufacturer (e.g. lower cost provider) the coordination is lost. electronic trip breakers can be coordinated between 100A and 125A, to my knowledge the best fuse ratio is 1.5X. And yes, electronic trip breakers are expensive.

Ok, that makes more sense now But the price is better

The 2x limit is at the fully rated maximum 3-phase bolted fault current, which only occurs as part of a wiring error. A breaker can be reset hundreds of times for the more common 'overload' fault. The real problem is not knowing what happens in between these fault levels.

I agree, but I have heard of cases where breakers have exploded within their rated AIC. The problem with breakers is that the internals become glazed even on low level faults. Unless the breaker has some means to see its history, its a gamble.

Did you just say that for 95% of probable faults, breakers are better?

In some ways. But if the fuse is used in conjunction with an automatic opening switch then Id call that a win-win.

 

[jim dungar]

In some ways. But if the fuse is used in conjunction with an automatic opening switch then Id call that a win-win.

Which brings us back to the marketplace. Over 100 years and no 'automatic opening fused switch', especially not in the <200A <600V world.

 

[mbrooke]

Which brings us back to the marketplace. Over 100 years and no 'automatic opening fused switch', especially not in the <200A <600V world.

But doesn't large fused switchgear have a switching disconnect?

 

[Tony S]

For MV they do. A fuse with an explosive cap fires a pin against a trip bar to open the other two phases.

For LV the fuse in the pictures I posted earlier has a micro switch across the two threaded lugs on the fuse. That opens the supply (in theory, I had one go wrong and it got interesting.)

https://www.youtube.com/watch?v=yTdngnsyNSE

 

[purevoltage]

I was looking for some fuse info and found this thread. Very interesting discussion. I think one thing I did not see you guys mention was the arc flash gear you should have on for a fuse disconnect. Exposed live electrical parts would constitute some sort of arc flash boundary. Were a breaker if the dead front and panel cover are on you don't have to be in arc flash gear. Those are my two cents

 

[GoldDigger]

I was looking for some fuse info and found this thread. Very interesting discussion. I think one thing I did not see you guys mention was the arc flash gear you should have on for a fuse disconnect. Exposed live electrical parts would constitute some sort of arc flash boundary. Were a breaker if the dead front and panel cover are on you don't have to be in arc flash gear. Those are my two cents

Only if the dead front and cover are certified by the manufacturer as arc fault protection. Otherwise your PPE would have to provide ballistic protection against the flying cover as well as thermal protection. And then flash would follow the cover.

 

[romex jockey]

Fused disco's usually come with more AIC for less $$$

also, i thought i caught wind of some '17 code cycle fuse amendment ....

not sure....

~RJ~