General > General Technical Chat
HRC Fuses
mitpatterson:
I hear Dave talking all the time about HRC Fuses in multimeters he reviews and I have a few questions:
* I know HRC means High Rupture Capacity(or something similar), but what good is that in a meter? it not like the glass breaking on a normal meter is going to cut you until you take it apart, or am i missing something?
* And if they are that much better, can you just replace the glass ones in a normal meter with HRC fuses of the same size and ratings? or is there something special there that would make this not possible? This may be a bit "Noobish" but i appreciate you reading this and replying. Also if this should be in a different section(like the beginner one or the blog one) feel free to have a mod move it where it goes.
Thanks
Psi:
As i understand it... when a normal glass fuse blows under extreme load. ie, you put your meter across something that can supply 1000's of amps at high voltage. The fuse wire inside instantly vaporizes creating massive pressure and heat which explodes outwards melting and breaking the glass case. You then have a shower of molten metal and glass moving out at high speed in all directions and cutting through the multimeter's plastic case as it goes, like a shaped charge cutting through the armour on a tank. So not the kind of thing you want to happen while you're holding the meter. HRC fuses don't explode like that, they are designed to handle the pressure safely.
ok, that was probably a bit overly dramatic, it's pretty uncommon for them to actually do that but you get the idea, glass fuses break easier making a mess inside your meter that you have to clean up and which may damager other parts inside or hurt you throught the case. HRC fuses are designed to prevent flashover, the sand inside them melts into glass and because glass is an insulator they stop any arcs from trying to keep the connection.
Uncle Vernon:
--- Quote from: mitpatterson on January 03, 2011, 03:50:57 am ---
* I know HRC means High Rupture Capacity(or something similar), but what good is that in a meter? it not like the glass breaking on a normal meter is going to cut you until you take it apart, or am i missing something?
--- End quote ---
Yes you are missing something, the other thread in this forum has gone off on quite a tangent about CAT ratings and life safety, these are far from the sole reason for selecting HRC fuses. In general semiconductors and PCB tracks are an excellent means of protecting standard rated fuses in electronic devices. A HRC fuse is designed to interrupt current flow in as few cycles as possible. HRC applies as much to the ability to respond quickly as it does to the ability to ensure high fault current flow can be broken
Cheap meters use the audible THARWARPPP!!! indication of this error and are reset by substituting a replacement meter with its smoke still intact. Your Fluke or better meter can generally cope with the inadvertent resistance measurement across the mains at least for a few seconds while flashing their display to indicate PEBMAC error.
And of course there is the inevitable meter left on amps before a mains measurement. Try that with a standard fuse and the current shunt and PCB tracks will become a shiny patch on the back of the meter case. That is the primary reason for selection of HRC. As CAT rating increase so too do the specifications but what is stated above still applies.
--- Quote from: mitpatterson ---
* And if they are that much better, can you just replace the glass ones in a normal meter with HRC fuses of the same size and ratings? or is there something special there that would make this not possible?
--- End quote ---
They are much better if the task is equipment protection, equally they are much worse if used in applications such as motor starting or capacitor charging. Can you replace the glass fuses in a multimeter with HRC fuses of a similar voltage and current rating? Of course provided you can find ones of suitable dimensions. You can find 00 and 3AG sized HRC fuses, but don't forget to top up the credit on the Visa Card before purchase. But sure you can put a $20 fuse in a $35 Dollar meter.
mitpatterson:
--- Quote from: Uncle Vernon on January 03, 2011, 04:30:14 am --- Can you replace the glass fuses in a multimeter with HRC fuses of a similar voltage and current rating? Of course provided you can find ones of suitable dimensions. You can find 00 and 3AG sized HRC fuses, but don't forget to top up the credit on the Visa Card before purchase. But sure you can put a $20 fuse in a $35 Dollar meter.
--- End quote ---
oh, wow, i didn't realize there where that much more expensive. Foe example if i wanted to find some at say, Mouser(http://www.mouser.com/Circuit-Protection/Fuses/_/N-5g3l/ ) what would i choose to find them? i don't see a HRC catagory, is there another name for them?
Oh and for the record, i got a $55 meter, lol
Uncle Vernon:
--- Quote from: mitpatterson on January 03, 2011, 04:43:37 am ---
--- Quote from: Uncle Vernon on January 03, 2011, 04:30:14 am --- Can you replace the glass fuses in a multimeter with HRC fuses of a similar voltage and current rating? Of course provided you can find ones of suitable dimensions. You can find 00 and 3AG sized HRC fuses, but don't forget to top up the credit on the Visa Card before purchase. But sure you can put a $20 fuse in a $35 Dollar meter.
--- End quote ---
oh, wow, i didn't realize there where that much more expensive. Foe example if i wanted to find some at say, Mouser(http://www.mouser.com/Circuit-Protection/Fuses/_/N-5g3l/ ) what would i choose to find them? i don't see a HRC catagory, is there another name for them?
Oh and for the record, i got a $55 meter, lol
--- End quote ---
They can be that expensive one off retail in AU anyway. I'm not in the habit of stressing my meters so I don't see too much need for a bulk buy. You can often get fast acting glass fuses which are better than standard but not up to being classified as HRC.
Try a google search on 3AG HRC.
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