circuit breaker vs. fuse

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maxall777

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My question is when should you use a circuit breaker and when should you use a fuse, or doesn't it matter as long as there sized right.
 
It can also depend on who you ask..... each "side" can provide you a good sell on their product....
Zog may disagree with me and he is certainly more qualified, but often it appears to me that it comes down to (a) the obvious ability to "reset" a breaker vs changing a fuse; (b) possible greater fault current limitation with fuses in some cases and (c) price, but as he said the discussion could take pages when you consider such things as selective coordination, series ratings, etc.
 
maxall777 said:
Lets say i have a machine and its full load is 60amps does it matter if i use a breaker or fuse.
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It certainly could. Often times the machine manufacturer will have a preference.
You need to look at the avilable fault current and the withstand rating of the machine as well as other factors.
 
do you have a schematic for the machine?
what does it indicate?
are you considering changing an existing machine?
why, blowing too many fuses and breaker is easier to reset? :D
 
hillbilly1 said:
The fuse manufactures say that properly rated fuses will reduce the incident energy of an arc flash greatly versus a breaker.
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And the breaker manufacturer's say that a properly rated breaker will reduce the incident energy of an arc flash greatly versus a fuse.
They are both correct. There is no single 'always right' answer.
It all depends on the amount of fault current and the time it takes the device to open. But at about 200A and below, both will have similar results.

But to the OP question, unless there are manufacturers specs saying other wise, at 60A it really doesn't matter which type of device you choose.
 
hillbilly1 said:
The fuse manufactures say that properly rated fuses will reduce the incident energy of an arc flash greatly versus a breaker.
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Sure they do, they sell fuses. They make current limiting fuses the magic cure for arc flash, in some cases they are very effective, in other cases not. What they fail to mention is the current needs to be in the current limiting range to be effective and with arcing currents being lower than bolted fault currents that is often not the case.
 
augie47 said:
It can also depend on who you ask..... each "side" can provide you a good sell on their product....
Zog may disagree with me and he is certainly more qualified, but often it appears to me that it comes down to (a) the obvious ability to "reset" a breaker vs changing a fuse; (b) possible greater fault current limitation with fuses in some cases and (c) price, but as he said the discussion could take pages when you consider such things as selective coordination, series ratings, etc.
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I agree with all of that, well said. There is not a straight answer to which is better, it all depends on what you want to accomplish. It is like asking which car is the best?
 
zog said:
Sure they do, they sell fuses. They make current limiting fuses the magic cure for arc flash, in some cases they are very effective, in other cases not. What they fail to mention is the current needs to be in the current limiting range to be effective and with arcing currents being lower than bolted fault currents that is often not the case.
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Thats why I prefaced my comment with "Fuse manufactures", it just depends on who is selling what.:roll: You sell breakers, right? :)
 
augie47 said:
(a) the obvious ability to "reset" a breaker vs changing a fuse; (b) possible greater fault current limitation with fuses in some cases and (c) price, but as he said the discussion could take pages when you consider such things as selective coordination, series ratings, etc.
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(d) Possiblity of a fuse single phasing a load.
 
And other things too, regarding arc flash the Instantanous functions can be an effective means of mitigation, clearing the fault as fast or faster(3-5 cycles) than most non current limiting fuses. In a substation you typically do not have INST trips on you main breakers, only on the feeders, because a fault on a bus duct or cable run could cause the main to trip and shut down half the plant, no delays on the INST trips so no way to coordinate them. So the main has a Short time delay which can lead to some very high arc flash levels.

Now if you have some top of the line communicating trip units with ZSI the breakers can "talk" to each other. A fault occurs on a bus duct, feeder and main breakers both see the fault current rise above the INST pick up points, so the main breaker says "Hey! Feeder breaker, do you have an INST signal?" if the feeder says "Sure do!" the feeder trips and the main does not. If the feeder says "Huh?? What INSt trip?" the main will trip.

A poor mans version of ZSI is "maintenence switches" which basically enables a temporary INST trip when the system is enabled (Usually a pad lockable switch) when "work" (Like opening and/or racking a feeder breaker for LOTO) needs to be done. This flip of a switch can reduce arc flash levels from 4 or worse to 1 or 2 in most situations.
 
As my input to this never ending debate, I always like to point out one important fact about fuses.

All of the benefits they can provide go right out the window when someone can't find the right one and replace it with the next size up, or worse yet, a large bolt, a piece of EMT or copper pipe.

copper_fuse2.jpg


I have never seen that happen with a breaker.
 
Jraef said:
As my input to this never ending debate, I always like to point out one important fact about fuses.

All of the benefits they can provide go right out the window when someone can't find the right one and replace it with the next size up, or worse yet, a large bolt, a piece of EMT or copper pipe.

copper_fuse2.jpg


I have never seen that happen with a breaker.
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So true but they will still just snap in a higher amp breaker when it starts tripping
 
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