Best Practice: Fuses vs. Breakers?

zacslade

Member
Join Date
Oct 2014
Location
Phoenix, AZ
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84
Hi all,

It seems to me that breakers are invariably more convenient than fuses. Fuses are difficult to remove, and if they discharge then they have to be replaced, so you have to have the right kind in stock, etc, etc, etc.. With a breaker, you just flip the switch.

When is a fuse necessary instead of a breaker?

Thanks!
 
Hi all,

It seems to me that breakers are invariably more convenient than fuses. Fuses are difficult to remove, and if they discharge then they have to be replaced, so you have to have the right kind in stock, etc, etc, etc.. With a breaker, you just flip the switch.

When is a fuse necessary instead of a breaker?

Thanks!

What type of applications are you thinking of? VFD line protection, control circuit protection? Depending on how they are being used and what you are trying to achieve will make a big difference.
 
It depends on several factors, to highlight the quality of the protection you want and of course the cost.

If for example you want to protect a motor and its VFD then better an adequated breaker.

But for example to protect a heating resistors with a consumption of hundreds of amps then surely it will be much cheaper to use fuses.
 
That was a fairly good app note you linked to, tarik1978. An unbiased opinion that laid out the pros and cons in a well organized manner. I liked it.

Personally, I'm a fuse guy as long as you can use good quality disconnecting fuse holders, especially for branch circuit protection. In today's era of SCCR it is much easier to achieve an SCCR that makes life easy for the end user using fuses than using circuit breakers, at least at a reasonable cost. I personally don't perceive any benefits to be had from circuit breakers over fuses. Once you are into supplementary protection I can be swayed either way pretty easily.

A specific point the app note made that I wholeheartedly agree with is that using ease of recovery from an overcurrent event as a selection criteria is looking at the issue from the wrong end. If you are recovering from overcurrent events so often that ease of recovery from that event is a consideration, maybe you should address the cause of the overcurrent event. Those events shouldn't be occurring at all. If they are there are occurring, repair of the cause of the overcurrent event (cut wires that shorted, blown electrical component, etc) usually requires at least one order of magnitude more time to fix than resetting of the overcurrent protection, with very few exceptions.

Keith
 
The biggest problem with fuses.....finding and getting the one you need.....AND the correct size and type.
You do not know how many jobs I have been on that someone put time delay fuses on SCR circuits. There are some very fast electronic CBs out now.
Worse is ...."Well it was a 2 Amp and all I could find in stock was a 25 Amp.....and it fit."
 
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There are positives and negatives for each. I'd say most of it depends on application.

For instance, when it comes to fuses they have some advantages. They tend to be cheaper in the short-term. If a circuit is designed correctly, it really shouldn't blow. If you change a motor from 1HP to 2HP, you can use the same fuse block and just pop a new properly sized fuse in.

Circuit breakers are convenient when they trip. You can just flip them back on. While that sounds like a positive, it can also be troublesome and people (in my experience) aren't as likely to fix the problem, since it isn't costing them anything (new fuses). The other downside is, if you swap from a 1HP to 2 HP motor, you may have to get a whole new circuit breaker (unless you were smart and got one with an adjustable range)

Another great property of fuses (properly sized ones) is the SCCR rating. Circuit breakers will usually be between 10kA - 65kA while fuses usually start around 100k. If your customer has a high SCCR requirement, fuses are a no-brainer.
 
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There are currently circuit breakers with Z tripping curve suitable for semiconductor protection but I think they are very expensive
 

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