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Suitability of fuse for multimeter

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Gasboss775

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As a result of carelessness when measuring current I succeeded in blowing the fuses in all of my multimeters over a period of 2 to 3 years.
I note that my multimeters require a 500mA fuse it's a 5X20 mm "FF" type fuse. Would there be a problem with using a 500mA "F" type fuse as a replacement?
 
Quick versus very quick...how much did the multimeters cost? If less than the cost of the fuse, I'd go ahead and use the F or buy a new one. If cost was substantially more, I'd use the fuse called for by the manufacturer. My multimeter was in the $100 category, and I had to replace the fuse once. I used the proper replacement.

The fuse protects the meter, and it protects you from an overload that might cause smoke or fire. I suspect the F-type would suffice for the latter purpose.

John
 
Quick versus very quick...how much did the multimeters cost? If less than the cost of the fuse, I'd go ahead and use the F or buy a new one. If cost was substantially more, I'd use the fuse called for by the manufacturer. My multimeter was in the $100 category, and I had to replace the fuse once. I used the proper replacement.

The fuse protects the meter, and it protects you from an overload that might cause smoke or fire. I suspect the F-type would suffice for the latter purpose.

John

Thanks John,

I have 4 meters, 3 handheld, two of which were reasonably expensive ( around £50 / $75 about 20 years ago ) the third handheld one was cheap. The bench one was around £130 / $200, so I'd definitely want the proper fuse for that one! Haven't actually looked at the prices of these FF fuses, rumour has it , they're expensive. I'm about to have a look.
 
Multimeter fuses are not just to protect the multimeter. They are also to protect the user.

I've blown a few £5 fuses in multimeters. The fuses are often 30 x 10 mm, rated to 500 mA to 15 A, but usually with a 100,000 A breaking capacity. The idea is that if you manage to get a really big fault current, the fuse will still break it OK. If you use something less capable, the current will arc across the fuse and not be broken. Then the user realises and pulls the leads from the supply, and the current arcs to the leads, followed by the current arcing from where one lead was connected to where the other lead was connected, and then the current can really increase.

Where I used to work there were some serious 415 V supplies. Someone used a meter that wasn't fused to check the voltage on the bus-bars. The resulting arc trashed the entire electrical cabinet, melted the ceramic of some big fuses, and put 3 people in hospital. 5 years later, on the forehead of one of them, you could still see where his safety helmet had protected some areas of his face and not others. Apparently the multimeter didn't even look damaged.

I know most people on this forum won't have access to supplies with that sort of power, but I would always use the right fuse type for a multimeter, and be very wary of using a cheap multimeter on supplies with large potential short circuit currents.
 
It looks to me that "very fast acting" = FF according to the datasheet, and that is the description:
upload_2015-12-2_12-30-28.png


So, I would presume it is equivalent and would work.

John
 
Where I used to work there were some serious 415 V supplies. Someone used a meter that wasn't fused to check the voltage on the bus-bars. The resulting arc trashed the entire electrical cabinet, melted the ceramic of some big fuses, and put 3 people in hospital. 5 years later, on the forehead of one of them, you could still see where his safety helmet had protected some areas of his face and not others. Apparently the multimeter didn't even look damaged.

I would never have thought that such a destructive arc could form from as low as 415 volts, then again once the arc is established it has an incredibly low resistance ( negative resistance? ) and with bussbars presumably tens of Kiloamps could be sourced. I expect the individuals concerned were a lot more cautious after that!
 
I would never have thought that such a destructive arc could form from as low as 415 volts, then again once the arc is established it has an incredibly low resistance ( negative resistance? ) and with bussbars presumably tens of Kiloamps could be sourced. I expect the individuals concerned were a lot more cautious after that!
From what I understand, all the electricians across the company were more cautious after that.
 
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