I know it's an old thread, but it resonated with me. Have been tracing a starter/alternator/battery issue and toasted my old trusty sperry multimeter. At first didn't realize my mistake but then after the burnt smell I suspected I blew the fuse and then read up and understood the mistake. Opened up the multimeter and realized a fuse was the least of my problems
It was fried.
So I bought a nice Klein MM1000 and accidentally blew the fuse on it (two ways - one by accidentally leaving it in current setting while intending to test voltage, and also b/c the current measurement was spiking cyclicly b/w Amps and mA while I was in the mA setting and didn't realize it at the time).
Then realized that the Klein had the expensive and hard to find in a pinch High Energy fuses (same as fluke). I'm talking $15 for the 11A and $10 for the 440ma fuses individually (go to ebay for packs of 5).
I loved the Klein but knew I'd blow fuses in the future and didn't want to deal with hard to find and costly fuses. So I got annoyed by these fuses and looked into it further - why did some $60-$100 multimeters use the hard to find fuses and some use "easy to find at radio shack" fuses? And what constitues a "High Energy" fuse and do I really want/need it?
I found some good literature on the topic below:
1)
http://support.fluke.com/find-sales/Download/Asset/2041429_6001_ENG_A_W.PDF ("Choosing the correct fuse for your tester") - see the section "When does a tester become a grenade?". Basically
2)
http://support.fluke.com/find-sales/download/asset/1263690_6116_eng_h_w.pdf ("The ABCs of Multimeter Safety")
3)
http://cp.literature.agilent.com/litweb/pdf/5990-4578EN.pdf ("Think safety when selecting a handheld digital multimeter")
4)
http://www.newark.com/pdfs/techarticles/agilent/increasingSafetyForInstallationMaintenance.pdf ("Going The Extra Mile To Ensure Safety Of Field Engineers In I&M Application")
Here's more from the first fluke link:
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When does a tester become a grenade?
Manufacturers specify in manuals and often on the meter the required amerage, interrupt and voltage ratings for replacement fuses. If you select a fuse without these ratings, or even worse, place a wire around the fuse connections, believe it or not, you have just created a thermal hand grenade. You just need the right conditions to set it off.
You probably won’t get an explosion while working on a printer, computer, copier or equipment that has its own power supply (CAT I). You might even get away with working on branch circuits (CAT II) without setting it off. These two environments are fairly low energy and often have built-in fuse protection, circuit breakers and over-current protection circuits. However, its not a good idea nor a safe way to work. When you move to an electrical distribution cabinet (CAT III) or primary feed-lines (CAT IV), the protection circuits change significantly. In the distribution panel you have breakers between you and the power company rated at hundreds of amps instead of the 15, 20 or 30 amp breaker on a branch circuit. When measuring voltage on the input side of a breaker panel at a residence, the protection is now back at the utility pole or the substation. These breakers can carry thousands of amps before opening and take considerable more time to open than a branch circuit breaker.
So when you accidentally leave the leads in the amps jacks and place the meter leads across one of these voltage sources without an appropriately-fused tester, you have put your life in grave danger.
The plasma fireball
In this situation, the short represented by the wrong fuse (or the wire wrapped around the fuse connections) and the test leads are fed by an almost unlimited amount of energy. The metal element in the fuse (or wire) heats up very quickly and begins to vaporize creating a little explosion. In the case of the wrong fuse, the fuse enclosure may burst open from the force of the explosion to find an unlimited amount of oxygen to fuel a plasma fireball. The test leads may also start to melt, and very quickly fire and hot metal gets on your hands, arms, face and clothing. How long the energy remains applied to the tester, the oxygen available and the presence of safety equipment like face shields and heavy gloves will determine how serious your injuries will be. This all takes place in milliseconds and leaves very little time to react to the mistake. If you’re lucky, you may be thrown clear of the leads or tester and thus break the circuit. But luck is not much to count on, especially when you could avoid the problem altogether by using the proper fuse.
Using the proper fuse
Specially designed “high-energy” fuses are designed to keep the energy generated by such an electrical short within the fuse enclosure, thus protecting the user from electric shock and burns. These high-energy fuses are designed to limit the length of time the energy is applied and the amount of oxygen available for combustion. Fuses can not only be designed to open at a specified constant current, but at an instantaneous high current as well. This high current is specified as “minimum interrupt current.” Fluke uses fuses with a minimum interrupt rating of 10,000 and 17,000 amps in their testers. If you take a CAT III 1000 V meter with the test leads in the amps jacks, you will have a series resistance of approximately 0.1 ohms (0.01 for the shunt, 0.04 for the test leads and 0.05 for the fuse and circuit board conductors) between the leads. Now when you accidentally place the leads across a 1,000 volt source, by Ohms Law you will generate a current of 10,000 amps (E/R=I, 1,000/0.1 = 10,000).
You want a fuse that will break that current and do it quickly. In addition to the specially designed fuse element, the highenergy fuse is filled with sand. The sand will not only help absorb the shock energy created by the exploding element, but the high temperatures (up to 10,000 °F) generated by the energy will melt the sand and turn it to glass. The glass coats the element and smoothers the fireball by cutting off the available oxygen, keeping you and the tester safe from harm. As you can see, not all fuses of the same amperage and voltage rating are the same. For your own safety you need to be sure the fuses you use are the ones the engineer designed into the tester. Always refer to the tester’s manual, or check with the tester manufacturer to ensure you have the correct fuse. You can always get replacement fuses for Fluke testers by ordering the part number listed in the tester’s manual. Your safety is worth much more than the money it takes to purchase the proper fuse for which the tester was designed.
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