Multimeter fuses

[tautech]

Before I would condemn the two-fuse system as problematic, .............

2 series fuses are a practical solution for protection of a measurement system where one might be inside the instrument and not readily accessible yet the other in an external cartridge type fuse holder at the rear of the instrument where it is one readily accessible and 2 a lesser rating to the internal fuse.
Either can be contained so not to blow plasma around delicate instrumentation when users make dumb errors.
Staging series fuse breaking characteristics is not difficult these days by using rapid or time delay fuses of slightly different amperages.

SDM3000 bench meters employ this strategy with internal 12A and external 10A slow and fast blow fuses.

[Fungus]

as a rule of thumb:
Regardless of what short-circuit-capability your transformer and the high-voltage network is, 3 meter of 1,5mm²  (somewhere between 15 and 16 AWG) singlephase 230V AC could only produce 2000 Amps short-circuit current due to the dampening effect of the thin copper...

Yep. That's basically the difference between CAT II and CAT III, i.e. the distance to the fuse box.

[Fungus]

if there is an issue, perhaps the fix is the one you suggested--updated fuse technology for the smaller fuse.  Here's a candidate with sufficient specs and it fits right in the same slot as the AGX-2.

https://www.mouser.com/datasheet/2/701/P404900rB_drawing-1633768.pdf

 

[joeqsmith]

2 series fuses are a practical solution for protection of a measurement system where one might be inside the instrument and not readily accessible yet the other in an external cartridge type fuse holder at the rear of the instrument where it is one readily accessible and 2 a lesser rating to the internal fuse.
Either can be contained so not to blow plasma around delicate instrumentation when users make dumb errors.
Staging series fuse breaking characteristics is not difficult these days by using rapid or time delay fuses of slightly different amperages.

SDM3000 bench meters employ this strategy with internal 12A and external 10A slow and fast blow fuses.

Assuming we are still talking cheap glass fuses used to protect a more expensive safety fuse so attempt to save a few bucks.....   

I've looked a some pretty cheap meters, many with glass fuses (marked CAT III 600V and up).  One meter I looked at had a blue condom  over it.   Maybe an attempt to contain the blast.   I wonder with an actual arc flash test, could you actually contain one reliably.   

Better just stop embellishing the meter's ratings.  With counties allowing the import of the shit, the markings basically are worthless anyway.  I'm actually surprised that top level companies don't lobby for this.   The hobbyist could still buy their properly CAT I rated meter with glass fuses for a couple of bucks.    Still what we have today isn't so bad.  I would imagine few industrial techs, electricians and the companies who hire them, are not running out to buy these low end products.     And the hobbyist who doesn't care about such things as arc flash can buy what ever meter they want and jump the fuses with wire to save a few dollars.  Life goes on....     

[tautech]

2 series fuses are a practical solution for protection of a measurement system where one might be inside the instrument and not readily accessible yet the other in an external cartridge type fuse holder at the rear of the instrument where it is one readily accessible and 2 a lesser rating to the internal fuse.
Either can be contained so not to blow plasma around delicate instrumentation when users make dumb errors.
Staging series fuse breaking characteristics is not difficult these days by using rapid or time delay fuses of slightly different amperages.

SDM3000 bench meters employ this strategy with internal 12A and external 10A slow and fast blow fuses.

Assuming we are still talking cheap glass fuses used to protect a more expensive safety fuse so attempt to save a few bucks.....   

A mixture and with different speed ratings:
SDM3000 family:
Rear panel fuse: 5x20 glass Littlefuse
Internal PCB fuse: 5x20 HRC Littlefuse

Pic of SDS3045X showing covered internal HRC fuse bottom left and external accessible fuse holder bottom right:

[joeqsmith]

CAT II 300V, no problem.  It's made for the lab not for an electrician.   Now is "... 2 series fuses are a practical solution for protection of a measurement system ..." for this particular meter actually true?  They claim 61326 and 61010.   Can you provide both reports?   

[tautech]

CAT II 300V, no problem.  It's made for the lab not for an electrician.   Now is "... 2 series fuses are a practical solution for protection of a measurement system ..." for this particular meter actually true?  They claim 61326 and 61010.   Can you provide both reports?

Maybe the factory has them on file as they no apparently longer list them on the websites but they do state this:

Information regarding product compliance is available on the datasheet for each product.
Contact your local Siglent office for more details if you have trouble finding what you need.
You can also write sales@siglent.com

Otherwise only this from the datasheet:
EMC Conforming to EMC (2004/108/EC) and EN 61326-1:2013
Safety IEC 61010-1; EN 61010-1; UL 61010-1; CAN/CSA-C22.2 No. 61010-1 Measurement CAT I 1000 V/CAT II 600 V
 

[bdunham7]

Better just stop embellishing the meter's ratings.  With counties allowing the import of the shit, the markings basically are worthless anyway.   

Very true, but IMO some of the markings are 'worthless' in a different sense as a result of the obsession with mains power, transients and arc-flash.   A completely non-mains derived source would appear to be CAT 1, but what is the hazard level of something like an 800 volt electric car battery or a 950 volt DC solar array?  Does CAT 1/1000V sound sufficient?  The fuses in the meters that I actually use -- including the ones I put in my old 8505A-- would appear to be sufficiently rated to not go nuclear on the DC solar array, but the battery would have me wondering what the maximum fault current was.  It would certainly give the 10kA or 20kA DC interrupt rating a good verification test.

For the vast, vast majority of these meters there is little to no chance of them actually going near any actual arc-flash hazard as defined by IEEE-1584.  And that's probably a good thing.

[bdunham7]

SDM3000 family:
Rear panel fuse: 5x20 glass Littlefuse
Internal PCB fuse: 5x20 HRC Littlefuse

Pic of SDS3045X showing covered internal HRC fuse bottom left and external accessible fuse holder bottom right:

Is that the way the SDS3065X is too, with a CAT 2/600V rating?  Because I don't think there are any 5x20 fuses like that with a 600 volt rating.  That and the interrupt ratings on that size are pretty low.  I'd like to see a 1kV 10kA fuse even on a CAT 1/1000V meter.

[joeqsmith]

CAT II 300V, no problem.  It's made for the lab not for an electrician.   Now is "... 2 series fuses are a practical solution for protection of a measurement system ..." for this particular meter actually true?  They claim 61326 and 61010.   Can you provide both reports?

Maybe the factory has them on file as they no apparently longer list them on the websites but they do state this:

Information regarding product compliance is available on the datasheet for each product.
Contact your local Siglent office for more details if you have trouble finding what you need.
You can also write sales@siglent.com

Otherwise only this from the datasheet:
EMC Conforming to EMC (2004/108/EC) and EN 61326-1:2013
Safety IEC 61010-1; EN 61010-1; UL 61010-1; CAN/CSA-C22.2 No. 61010-1 Measurement CAT I 1000 V/CAT II 600 V

Yeah I read the data sheet which is why I asked for the report.   I don't have that level of interest to try and hunt it down but thought that with your comment about it being a practical solution for protection of a measurement system, that you had data (the reports) to back up that statement was all.   If it were a handheld device, I may take a swing at it.   

[joeqsmith]

Better just stop embellishing the meter's ratings.  With counties allowing the import of the shit, the markings basically are worthless anyway.   

Very true, but IMO some of the markings are 'worthless' in a different sense as a result of the obsession with mains power, transients and arc-flash.   A completely non-mains derived source would appear to be CAT 1, but what is the hazard level of something like an 800 volt electric car battery or a 950 volt DC solar array?  Does CAT 1/1000V sound sufficient?  The fuses in the meters that I actually use -- including the ones I put in my old 8505A-- would appear to be sufficiently rated to not go nuclear on the DC solar array, but the battery would have me wondering what the maximum fault current was.  It would certainly give the 10kA or 20kA DC interrupt rating a good verification test.

For the vast, vast majority of these meters there is little to no chance of them actually going near any actual arc-flash hazard as defined by IEEE-1584.  And that's probably a good thing.

Not being a safety buff, I don't have the background required to answer your questions.  My guess is that when the standards were being developed, very little was being done with DC.  At least not to the scale we had with AC and that's were the concern was.   That said, I don't think they make those HRC fuses both AC and DC rated for the fun of it.   I would imagine designing a fuse for 1000V DC with a 30KA fault current came with a bit of research and cost.     

I would imagine anyone working with high voltages and high energy levels (AC or DC) knows what is required and has the proper training.  Myself, I am not an electrician and its rare I am involved with anything that's a concern.   Again, when I do, I use a meter with no fuses.   Clamp only.    For home, I just want the a meter that is robust enough that when I do something stupid, the meter doesn't go to the recycle bin.  This is why I test the meters at very low levels.   

[Kosmic]

I've looked a some pretty cheap meters, many with glass fuses (marked CAT III 600V and up).  One meter I looked at had a blue condom  over it.   Maybe an attempt to contain the blast.   I wonder with an actual arc flash test, could you actually contain one reliably.   

My old HP 974a (Rebranded Yokogawa) has something like that on the mA range. Always weird to see that they were trying to save a bit of money on a expensive meter like that. Then again it was mostly targeted at lab application where it's always CATII and lower.

[nightfire]

I was browsing the recent SIBA catalogue and noted some explanations in the preface section:

"4.1 The glass tube
If the maximum expected short-circuit current (prospective cur-
rent Ip) is not greater than 35 A or max. 10 Irat, then a miniature
fuse-link with an unfilled glass tube is used. This fuse-link has the
advantage of a relatively low voltage drop"

So it seems that maybe this version has been chosen to provide for a low voltage drop and therefore better accuracy/lower burden.

[nightfire]

Uhh- just looked a bit further with the 5x20mm fuses, and in short: the simple glass-tube fuses have a way lower resistance (and therefore heat dissipation) than their sand-filled ceramic counterparts. We are talking a factor of 3 or 4 here...