Best interrupting rating on 5x20mm 10A fuse for meter protection. - Page 1
Forum section: electronics / testgear

author: DX1
author_rank: Contributor
timestamp: March 27, 2023, 03:29:34 pm
content: Littlefuse do several 5x20mm fuses with 250V 1500A interrupting protection.Is this the best available? For use in multimeter to protect against accidentally applying current measurement to a voltage.Are any available with higher voltage/current interruption?Or are any multimeters available that can take 6.3x25mm BS1362 fuses(250V at 6500A interrupting protection)?

author: AVGresponding
author_rank: Super Contributor
timestamp: March 27, 2023, 05:28:33 pm
content: istr some of the Chinese brands use BS1362 fuses, my Uni-T 139C may, I'll have a look.EDIT: Ha, got distracted and forgot. Had a look now, it uses a 6x32 for the mA range, accessible through the battery door, and a 10A BS1362 for the 10A range, which you have to take the case apart to access.

author: Gyro
author_rank: Super Contributor
timestamp: March 27, 2023, 06:46:25 pm
content: Yes, 1500A 250V is the best you're going to find in 5x20mm.The UT61E is another one that takes BS1362 fuses (unless it's an uprated one with the big 20kA fuse and a 5x30mm mA fuse).

author: Alti
author_rank: Frequent Contributor
timestamp: March 28, 2023, 11:31:58 am
content: Quote from: DX1 on March 27, 2023, 03:29:34 pmYou misspelled the brand name or bought some really, really wonky fuses.Don't play with safety.Quote from: DX1 on March 27, 2023, 03:29:34 pmYou need to pick a solution adequate for application.Measurements in different environment require different protection measures, you know. If that is for laboratory environment, CAT I rated gear is adequate, 300V would do in your UK case. Here I would recommend IEC 60127-2/1 fuses. These are not rated for this exact voltage but as long as you stay below 1500A of prospective short-circuit current (PSCC), you should be safe.Just be aware those fuses, reliable, cheap and available in most grocery stores, are designed for <250Vrmsand<1500A PSCCandpower factor of 0.7 to 0.8.So no, you cannot charge 1F low ESR capacitor to 200V and get close to it with such meter because this energy is going to rupture the fuse, even without exceeding 1500A. The current during short-circuit has to ramp up slowly and be limited by reactance to give the link the time to interrupt the loop and pull down the arc well before current reaches 1500A. If you want to know more about "fuse abuse", ask mikeselectricstuff aboutdestructotronMCB. Same applies to playing with inductors, voltage must not raise too fast, and the energy dissipated has to be smaller than what it takes to melt quartz sand, before it evaporates, rupturing the housing.If you exceed parameters of the fuse, it is going to split the housing and then it might ruin your day. There are fuses that do not come with this tight current and voltage ramp-up limitation and can work even with very high and very low cos(phi) but these are not general purpose fuses designed for short-circuit and overload protection. Might work or might not work - just are not designed for the job and not tested for this.For CAT II or CAT III mains jobs - forget it. PSCC in my place is well over 2kA and I think UK single phase grid makes PSCC even higher than elsewhere.Get a clamp meter - use adequate tool for current measurements in distribution boards.