HRC Fuses

[NiHaoMike]

Still, high current accidents are quite possible at low voltages and not something you can simply disregard. Say the good old car battery. Brushless motors are also quite popular. LED lighting on larger scale may also involve high currents.

I still have a scar on my arm from 8 or so years ago when I tried to measure a PC power supply with a cheap meter set to amps. An unfused input can be dangerous even on some "safe" CAT I circuits.

[Kiriakos-GR]

I have the Extech EX330 meter

Yes the fuses are up to the specs , I just checked the manual of your DMM and your links.

[Kiriakos-GR]

Too much references about the IEC 61010-1 since 1.1.2004 ,
but the discrimination between  CAT I - II - III - IV , by it self it does not force any one to use HRC,
especially at CAT I & II .

And so even the cheapest meters can look as legal , if they wrote on them the true specs. 

Neilm , you had said that you had participate at multimeter testing.
Well this is " Internet " , and every one can say even that he is an astronaut .

Tell me something, at your testing at 4KV , how long time the voltage stayed at 4KV on the tests ?

[Neilm]

Neilm , you had said that you had participate at multimeter testing.
Well this is " Internet " , and every one can say even that he is an astronaut .

Tell me something, at your testing at 4KV , how long time the voltage stayed at 4KV on the tests ?

The high voltage is a pulse not a level. The peak of the pulse is dependent on the CAT rating of the instrument. 300V CATIII is (from memory) 4kV, 300V CATIV is 6kV, 600V CATIV is 8kV. The pulse is only a few microseconds long (I don't remember the exact length now but 60us rings a bell) with the rise and fall times specificed by another IEC standard. The pulse is superimposed on the 300V / 600V with a supply rating determind by the test you are doing. I will note that when we upgraded our facility at work the sub-station required upgrading.

The idea behind the test is that the pulse would cause a breakdown in the unit under test. This breakdown would then produce an ionised path of low resistance. This low resistance would then act as a short circuit to the mains supply that would then provide the energy to do damage. This test highlights problems with insufficient clearance within a unit, or with design problems with the protection circuit. For instance, if the protection circuit relys on a fuse the effect of that blowing can cause a very large voltage spike due to the inductance of the leads. This can bypass the protection if not clamped and cause a failure.

Yours

Neil

[Zero999]

The high voltage is a pulse not a level. The peak of the pulse is dependent on the CAT rating of the instrument. 300V CATIII is (from memory) 4kV, 300V CATIV is 6kV, 600V CATIV is 8kV. The pulse is only a few microseconds long (I don't remember the exact length now but 60us rings a bell) with the rise and fall times specificed by another IEC standard. The pulse is superimposed on the 300V / 600V with a supply rating determind by the test you are doing. I will note that when we upgraded our facility at work the sub-station required upgrading.

The idea behind the test is that the pulse would cause a breakdown in the unit under test. This breakdown would then produce an ionised path of low resistance. This low resistance would then act as a short circuit to the mains supply that would then provide the energy to do damage. This test highlights problems with insufficient clearance within a unit, or with design problems with the protection circuit. For instance, if the protection circuit relys on a fuse the effect of that blowing can cause a very large voltage spike due to the inductance of the leads. This can bypass the protection if not clamped and cause a failure.

You're right about the high voltage pulse arcing and causing a short circuit but I think the pulse itself could be dangerous.

An 8kV pulse linearly ramped up and down into 1k is is 1.92J which is pretty dangerous, think of a 33µF capacitor charged to 341V

[Kiriakos-GR]

I have awareness about the high voltage pulses , and I agree that mainly on the test are the PCB design problems ..

By supplying high voltage , you do not test fuses , but the PCB flaws and the complete design ,
if it survives or not.

 

 

[cybergibbons]

It's quite likely that the HRC fuse in most high end meters will take longer to blow that a fast-acting glass fuse.

Bollocks! Much of the ability to not rupture in entailed in interrupting flow of fault current in the shortest possible time!!!  That fault current wont just be flowing in the fuse it'll be flowing through the leads, the shunt the sockets and PCB all of which will let go spectacularly with sustained fault current! Many of the larger HRC cartridges have a rating of maximum number of cycles before interruption.

Sorry, this simply isn't true.

Most HRC fuses take a long time to blow at normal fault currents between 1 and 50 times rated as compared to a fast-acting fuse. There is a huge difference between operation under low current fault conditions (1-50 x rated current) and massive fault currents (10kA).

[Uncle Vernon]

It's quite likely that the HRC fuse in most high end meters will take longer to blow that a fast-acting glass fuse.

Bollocks! Much of the ability to not rupture in entailed in interrupting flow of fault current in the shortest possible time!!!  That fault current wont just be flowing in the fuse it'll be flowing through the leads, the shunt the sockets and PCB all of which will let go spectacularly with sustained fault current! Many of the larger HRC cartridges have a rating of maximum number of cycles before interruption.

Sorry, this simply isn't true.


Most HRC fuses take a long time to blow at normal fault currents between 1 and 50 times rated as compared to a fast-acting fuse.

Then I don't know how the hell your selecting your fuses but I'd suggest you buying something very sub-standard. perhaps your confusing ceramic bodied fuses or Motor-Start cartridges with HRC ones.

There is a huge difference between operation under low current fault conditions (1-50 x rated current) and massive fault currents (10kA).

So there is, but that does nothing to suggest that a HRC fuse by design should be slow to respond! To suggest there is, is insanity!
Where is the safety margin from extending the duration of a fault current condition? That's right there is no reason! 

When you purchase a quality HRC fuse your not just buying arc quenching you are buying a device that has overall superior parameter. You're (or you should be) paying for a fuse with a superior element material one that will rupture quickly albeit not spectacularly.

[Kiriakos-GR]

The first time that I have seen HRC fuses ,  was on Fuse box  that secures motors ...

Its known that in motors you do not expect instant Cut off !!

Even so , the shape looks to have nothing to do with the speed .
I bet that at 3 phases 380V , the HRC design is used , because it is high voltage " friendly " .

high voltage " friendly "  = 500V   ( industrial use )

If the HRC can stand up to 1000V or more , its an extra benefit of this design ( shape ).
And actually of how long they are , that is related with the PCB clearance , by using the resistance of air  as isolator.

And so if we could make the first list of benefits of using HRC, it could be :

1) Safe design to used for 380V installations and above.
2) Space saving design .. for low current  up to 25A  
The HRC fuses boxes that I have see , its made by plastic !!
And in multimeters we have the open type metallic PCB base.
3) Space saving design .. for aluminum panel boxes ( if you plan to build an AC stabilizer )
or an portable industrial device. 



 

[Uncle Vernon]

The first time that I have seen HRC fuses ,  was on Fuse box  that secures motors ...

Its known that in motors you do not expect instant Cut off !!

In Australia those were always know as motor starts. Which were specifically designed to endure a reasonable number of over-current start cycles. What we'd always regarded as standard HRC came in the exact same physical format. And plenty were sacrificed by being used instead of motor starts.

Even so , the shape looks to have nothing to do with the speed .

It does and it doesn't. As fault current control requirements rise you ultimately have to settle for a physically larger device.

But yes you are quite correct in the sense that for a given fuse size you can get a number of different ratings of a number of different applications.

If the HRC can stand up to 1000V or more , its an extra benefit of this design ( shape ).
And actually of how long they are , that is related with the PCB clearance , by using air resistance as isolator.

It's of particular advantage if your trying to secure or maintain CAT ratings for your device.  These topics started around multimeter fuses and make no mistake the speed of the fuses such as those you've pictured previously is one of the reasons better meters do not let the smoke out very often. 

IF HRC fuses were routinely as slow as has been claimed do you thing Fluke etc would have risked not adding some 15c fast acting fuses to supplement the HRC ones used? The don't add them because they don't need them, the fuses selected are lightning fast when they need to be. I've seen plenty of cheapo meters with intact glass fuses and vapourised PCB current tracks, You'll seldom if ever see a quality HRC fused meter with the same outcome.

[Kiriakos-GR]

Well every conversation about HRC fuses and multimeter's  so far,
it had the fate to not lead anywhere .
That's why I had bring industrial examples about the usage of HRC,
so to make this one more wide as conversation.

Its good that we agree on the  " HRC as motor starts ".

The 95% of the HRC fuses that any one will easily locate on the market ,
it will be the slow ones for motors.

And if we start thinking , as the only known as Fast Fuses ( HRC type ) manufactures the BUSS and SIBA,
this conversation will end prematurely too.

Because we end up, at the two known brands that they monopolize the market ,
and control the pricing too .


What I am trying to do with all those conversations , are to investigate if there is another one player at the  Fast Fuses ( HRC type ), that we do not know about him !!

[Uncle Vernon]

Its good that we agree on the  " HRC as motor starts ".

The 95% of the HRC fuses that any one will easily locate on the market ,
it will be the slow ones for motors.

I don't agree with the 95%, I've always had to specifically order Motor-Starts. There are any number of suppliers for industrial ones. Flag ended, offset flag ended. Screw fit for those rotten old Red-Spot frames.

Back to a replacement suitable for meter fitment, I use so few  it's hardly been a concern. I treat it like a $20 "you wont do that again for while tax".

Not lending your meter will solve most instances of need! Even Especially to other techs or Sparkies, they know fuses are expensive so they'll seldom own up to blowing one of yours.

[Kiriakos-GR]

Back to a replacement suitable for meter fitment, I use so few  it's hardly been a concern. I treat it like a $20 "you wont do that again for while tax".

Not lending your meter will solve most instances of need! Even Especially to other techs or Sparkies, they know fuses are expensive so they'll seldom own up to blowing one of yours.

       

More Fuses on DMM gets burned when the meter are new ,  common mistake = of using the wrong Amperes input ..

At my 24  years on the field , I must have burn about four fuses on several meters,
I bet that my " Burning rate " are minimum .

But I have not yet burn an Fluke one , on this I am still " virgin " .    

[Uncle Vernon]

Back to a replacement suitable for meter fitment, I use so few  it's hardly been a concern. I treat it like a $20 "you wont do that again for while tax".

Not lending your meter will solve most instances of need! Even Especially to other techs or Sparkies, they know fuses are expensive so they'll seldom own up to blowing one of yours.

       

More Fuses on DMM gets burned when the meter are new ,  common mistake = of using the wrong Amperes input ..

At my 24  years on the field , I must have burn about four fuses on several meters,
I bet that my " Burning rate " are minimum .

But I have not yet burn an Fluke one , on this I am still " virgin " .    

I've had a fluke of some description since the mid 80's, cannot say I've ever destroyed one in use. (Having your meter run over by a fork-lift or bumped into a brine bath cannot really be described as in use.)  As for fuses over all those years I'd say my count was about 6. Two of which I'll own up to being the perpetrator of the dumb act. I've lost count of how many $100 meters I've seen blasted over a similar time frame.

Long before the days of OH&S (save them from themselves) nonsense, most employers learnt that providing Flukes (or equivalent) was the better option from a purely economic perspective.

[cybergibbons]

Much of the ability to not rupture in entailed in interrupting flow of fault current in the shortest possible time!!!

No, the ability to interrupt at massive fault currents is partly due to quickly stopping the flow of current. There are a lot of other factors. But at normal fault currents the time that it takes to interrupt doesn't matter - the fuse isn't going to exploded anyway.

Then I don't know how the hell your selecting your fuses but I'd suggest you buying something very sub-standard. perhaps your confusing ceramic bodied fuses or Motor-Start cartridges with HRC ones.

I'm saying that the bulk ("It's likely") of HRC fuses are slower to blow than a fast-acting glass fuse. Look at the data sheets - you'll be hard pushed to find a HRC fuse as sensitive as a the best fast-acting glass fuses, especially if you walk into a standard electrical supplier. The two commonly available types in the UK are gG (general purpose) and gM (motor), and both are pretty slow acting compared to say, the input fuse on my audio amplifier, which is a normal glass type.

So there is, but that does nothing to suggest that a HRC fuse by design should be slow to respond! To suggest there is, is insanity!

By design, a HRC fuse is a tube packed very tightly with quartz sand. This hugely increases the amount of heat transferred away from the fuse element, as compared to wire in air fuses. Because a fuse element breaks using heat, this in turn means that the element takes longer to break as it is harder to make it hot. It really is the case that HRC fuses, by design, would be slower to respond. They need to use careful design to make them faster again - mainly by material selection and element notching.

Where is the safety margin from extending the duration of a fault current condition? That's right there is no reason! 

So why aren't all fuses quick blow then? A number of reasons:

• Anything with a start surge requires a slower response time
• Discrimination in a distribution system requires that upstream fuses take longer to blow than downstream
• Fuses blowing repeatedly means that fuses need replacing more often, in turn meaning more maintenance, and then opening up maintenance workers to higher risk of an accident.

[mitpatterson]

all i have to say is WOW, only like 6 replies or so in direct regards to the original questions, the rest.... a bunch of people refuting others point's..... well i guess is what happens when i ask on a engineering forum ehh?, anyways, carry on, its interesting, and for someone who knows a bit more than i do probably interesting, lol.

[Uncle Vernon]

No, the ability to interrupt at massive fault currents is partly due to quickly stopping the flow of current. There are a lot of other factors. But at normal fault currents the time that it takes to interrupt doesn't matter - the fuse isn't going to exploded anyway.

In our multimeter scenario the speed of response is everything, how many half cycles of fault current will the components of the device sustain before something gives way explosively. We are talking a hand held device here.

I'm saying that the bulk ("It's likely") of HRC fuses are slower to blow than a fast-acting glass fuse. Look at the data sheets - you'll be hard pushed to find a HRC fuse as sensitive as a the best fast-acting glass fuses, especially if you walk into a standard electrical supplier. The two commonly available types in the UK are gG (general purpose) and gM (motor), and both are pretty slow acting compared to say, the input fuse on my audio amplifier, which is a normal glass type.

The bulk of ? Now that is somewhat different from your prior statement that my reference to fast action simply saw not true! It appears the goal post are being shifted now. And then we add terms "standard electrical supplier" and "commonly available types" we were after discussing the application of a specialist fuse and its use in a specialist device!  HRC fuses by application will seldom be a retail commodity. A great many of the HRC fuses used particularly those used around semiconductors will be fast acting.

 

By design, a HRC fuse is a tube packed very tightly with quartz sand. This hugely increases the amount of heat transferred away from the fuse element, as compared to wire in air fuses. Because a fuse element breaks using heat, this in turn means that the element takes longer to break as it is harder to make it hot. It really is the case that HRC fuses, by design, would be slower to respond. They need to use careful design to make them faster again - mainly by material selection and element notching.

No it doesn't make the case that HRC fuses are slower by design. There is considerable effort placed into the design characteristics of the fusible element in terms of it's dimensions, material selection and tolerance. That sliver of wire in a good HRC is not the same random chunk of nichrome you'll find in hardware store glass fuses. And yes that careful design is applied and yes it's another contributor to the comparatively higher prices of HRC fuses.

So why aren't all fuses quick blow then? A number of reasons:

• Anything with a start surge requires a slower response time
• Discrimination in a distribution system requires that upstream fuses take longer to blow than downstream
• Fuses blowing repeatedly means that fuses need replacing more often, in turn meaning more maintenance, and then opening up maintenance workers to higher risk of an accident.

And the start-up surge of a test instrument is? - Not applicable
Upstream systems? we are talking multimeters remember, what has upstream systems got to do with it?
Risks due to fuse replacement? Why not have all our fuses replaced with nails then or spent rifle cartridges, that'll be much safer, for sure. If a correctly sized fuse is blowing repeatedly then it is doing it's job meaning other aspects of the design or installation require attention.  I've seen more than a few contactors blown of the gear tray of a switchboard because some maintenance person decided motor start fuses would be a good idea and in doing so exceeded the duty cycle rating of the electric controls. If a fuse blows on a regular basis you need to ascertain why. 

[Uncle Vernon]

all i have to say is WOW, only like 6 replies or so in direct regards to the original questions, the rest.... a bunch of people refuting others point's..... well i guess is what happens when i ask on a engineering forum ehh?, anyways, carry on, its interesting, and for someone who knows a bit more than i do probably interesting, lol.

True, to answer you original question. Fuses ain't necessarily Fuses . If a meter has glass cartridge fuses it's unlikely the manufacturer paid much concern to safety in use or misuse of the device.

Would you gain advantage fitting your meter with better fuses? Perhaps? However you will need to check the spec sheets to make sure your better fuse is better in all the relevant parameters.

My advice for what it is worth is be careful, which you should be doing anyway regardless of the meter you use or it's fusing. Don't use general purpose meters for serious applications which require a Cat III or Cat IV device.
Would I do the occasional mains presence test with a cheap meter? Yes at a pinch and with a lot of respect for the situation.

Remember no meter, lamp, buzzer, volt-stick will confirm a conductor as safe to touch! They can only confirm it is not so.

Working with anything that is above ELV (32V maximum) or anything capable of more than a few hundred milliamps requires a healthy degree of respect and understanding.

To summarise, if it was my meter and I was in a similar situation I'd leave the glass fused meter as the manufacturer intended, and remain mindful of this when deciding where i used it.   A HRC fuse will by no means guarantee you meter is now invincible, only careful design can achieve anything close to that.

[mitpatterson]

all i have to say is WOW, only like 6 replies or so in direct regards to the original questions, the rest.... a bunch of people refuting others point's..... well i guess is what happens when i ask on a engineering forum ehh?, anyways, carry on, its interesting, and for someone who knows a bit more than i do probably interesting, lol.

True, to answer you original question. Fuses ain't necessarily Fuses . If a meter has glass cartridge fuses it's unlikely the manufacturer paid much concern to safety in use or misuse of the device.

Would you gain advantage fitting your meter with better fuses? Perhaps? However you will need to check the spec sheets to make sure your better fuse is better in all the relevant parameters.

My advice for what it is worth is be careful, which you should be doing anyway regardless of the meter you use or it's fusing. Don't use general purpose meters for serious applications which require a Cat III or Cat IV device.
Would I do the occasional mains presence test with a cheap meter? Yes at a pinch and with a lot of respect for the situation.

Remember no meter, lamp, buzzer, volt-stick will confirm a conductor as safe to touch! They can only confirm it is not so.

Working with anything that is above ELV (32V maximum) or anything capable of more than a few hundred milliamps requires a healthy degree of respect and understanding.

To summarise, if it was my meter and I was in a similar situation I'd leave the glass fused meter as the manufacturer intended, and remain mindful of this when deciding where i used it.   A HRC fuse will by no means guarantee you meter is now invincible, only careful design can achieve anything close to that.

My main concern/question is basically, when and if I blow a fuse(which i blew the 10 amper 2 days ago while testing the current draw of a UPS(under no load) so yah, lol) should i replace it with a HRC/ceramic fuse or just buy another glass one?

[Kiriakos-GR]

@ cybergibbons

Has some good points about Glass Fuses ,
They are fast and easy to find , and they are in use for lots of years.
The HRC it could be called as  " New " player ..

But , the design of the porcelain fuse with the sand in it ,
its the older and well known.

Does the HRC mimics, the old classic design ?
And why?  

 

[Kiriakos-GR]

My main concern/question is basically, when and if I blow a fuse(which i blew the 10 amper 2 days ago while testing the current draw of a UPS(under no load) so yah, lol) should i replace it with a HRC/ceramic fuse or just buy another glass one?

The HRC fuses are larger in diameter than the Glass type , you can not install them in a Glass fuse holder.

[mitpatterson]

My main concern/question is basically, when and if I blow a fuse(which i blew the 10 amper 2 days ago while testing the current draw of a UPS(under no load) so yah, lol) should i replace it with a HRC/ceramic fuse or just buy another glass one?

The HRC fuses are larger in diameter than the Glass type , you can not install them in a Glass fuse holder.

I've asked this before, WHY, my glass ones measure 5 x 20mm, and the HRC/cermaic ones i found are the EXACT same size, granted even if they aren't HRC they are ceramic and fast acting, so probaly closer to HRC then the glass ones

[Kiriakos-GR]

they are ceramic and fast acting, so probaly closer to HRC then the glass ones

Ohh I see ,  yes ceramic 5 x 20mm and fast acting are an great choice ...

HRC its nothing magic , its just an specific size and shape of fuse.  

sample..

[Chasm]

Fuses have a whole set of parameters, the current is only one of them.

current rating
characteristic (how fast)
voltage
rupture current
physical size / form factor
...and some more less obvious ones, like contact residence or resistance

HRC, high rupture capacity, says nothing more than that they can (safely) rupture a high fault current. BUT, this current is very much dependent on the both the form factor and voltage.

Form factor, no SMD fuse will ever rupture 10kA. (Without being ruptured itself. )

Voltage dependeny, say the BUSS ABC20 type, a 20A 32mm ceramic tube (non HRC) fuse like the one in the middle of the picture above, has a rupture rating of:
125V DC: 10000A
125V DC: 1000A
250V DC: 400A

The difference is that the HRC fuses usually give their rupture rating at their maximum rated voltage.

You can also buy HRC fuses with different acting characteristics. (fast vs. slow)
Speed does not affect how much current they can rupture.

[cybergibbons]

In our multimeter scenario the speed of response is everything, how many half cycles of fault current will the components of the device sustain before something gives way explosively. We are talking a hand held device here.

One of my meters is 10A continuous rated, but can measure 20A for 30s. I'm sure it could take 50A in a surge without damage. I certainly wouldn't want to replace my fuse due to a half cycle of 20.01A going through my meter!

HRC fuses are generally slower to blow than glass fuses at low fault currents. Take the Cooper Bussman DMM-B 11A fuse that is used in some Fluke meters (a fast-acting HRC). At 1s, it's taking approx 7I to blow. Compare to a Schurter FSF-5 glass fuse (just a random selection), which at 1s has blown at 3I. Then go to 0.1s - the HRC fuse is at 10I, and then at 7I.

This is the fuse that Fluke specify, and it costs over 20 times more than the glass fuse. It blows more slowly from 2I to 10I.

If, and only if, you end up in a situation where the current is greater than 10I, will the HRC fuse blow quicker. Putting 100A+ through a meter at mains voltage isn't an everyday occurrence. I'd say most meter fuses are blown at much lower currents

The same is true for the Littelfuse FLU fuses, HRC fuses designed specifically for multimeters.

So, you have said:
* The fuses on meters must be quick to blow to protect the meter
* The quicker the better, as that is everything in protecting the meter

So, by extension, the HRC fuses specified by the manufacturers would be some of the fastest available if this were the case? So why aren't they? Why can I find quicker glass fuses?

The bulk of ? Now that is somewhat different from your prior statement that my reference to fast action simply saw not true! It appears the goal post are being shifted now. And then we add terms "standard electrical supplier" and "commonly available types" we were after discussing the application of a specialist fuse and its use in a specialist device!  HRC fuses by application will seldom be a retail commodity. A great many of the HRC fuses used particularly those used around semiconductors will be fast acting.

You stopped referring to HRC fuses in meters specifically a long time ago and started making general comments about HRC fuses.
 

No it doesn't make the case that HRC fuses are slower by design. There is considerable effort placed into the design characteristics of the fusible element in terms of it's dimensions, material selection and tolerance. That sliver of wire in a good HRC is not the same random chunk of nichrome you'll find in hardware store glass fuses. And yes that careful design is applied and yes it's another contributor to the comparatively higher prices of HRC fuses.

A lorry is slower by design than a car. Put a huge engine, nitrous, and modify the gearbox in a lorry and it can beat most cars. But it's taken a lot of extra effort, and it still doesn't go round corners as well.

It's very difficult to make a HRC fuse quick, mainly due to the additional effort required to heat the fuse element. This is as a result of their design. You've pretty much backed up what I'm saying here.

Glass tube fuses aren't a random chunk of nichrome at all - take a look at some with a magnifying glass and you will see blobs and crimps to tune the response, coils to pull apart the fuse etc.

Risks due to fuse replacement? Why not have all our fuses replaced with nails then or spent rifle cartridges, that'll be much safer, for sure.

You deny that there is a risk involved with replacing fuses? Even in a multimeter, there are risks. What happens if the replacement is incorrect?