How to *NOT* replace a fuse in a multimeter - Page 1
Forum section: electronics / general

author: tamtam
author_rank: Newbie
timestamp: February 23, 2012, 02:37:31 am
content: Today I heard a strange sound in a Fluke179 (NOT MINE!!!). I opened it and found this. Someone *changed* the fuse and tried to *make it fit well*. I'm not sure if I should nowor

author: PedroDiogo
author_rank: Regular Contributor
timestamp: February 23, 2012, 02:47:25 am
content: Still, it's better than soldering a wire between the contacts I guess

author: Short Circuit
author_rank: Frequent Contributor
timestamp: February 23, 2012, 03:04:15 am
content: Odd way of fitting a standard fuseBending the clips is easier and more reliable.(Just don't use the DMM in high current systems)

author: tamtam
author_rank: Newbie
timestamp: February 23, 2012, 03:11:51 am
content: Quote from: PedroDiogo on February 23, 2012, 02:47:25 amHm ... I guess not. The disc can move to the other two terminals (Volt and COM) and make a short while you measure the voltage. In the factory where I found this, they have a lot of big drives (up to 700kW) and some other big consumer (HF welding). So the next fuse is maybe 200A, 400A, 800A or even higher by 400V or more (some drives have higher voltage).Or ... If you have such friends, you don't need enemies.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: February 23, 2012, 11:30:25 am
content: IndeedEven applies to general EE use. Wouldn't be very happy to kill a circuit because somedickhead upgraded a DMM with some metal parts inside.On the subject of replacing fuses with generic types, I figured I check the ratings of these fuses. And itappears these low-cost ceramic anti surge fuses can handle quite a bit of overload as well;Original 400/440mA fuseshave a 1kV rating, so they have a surge handling capability of 2.5kAare rated for 10kA.A ceramic 500mA fuse likehttp://nl.rs-online.com/web/p/cartridge-fuses/7211597/is rated for 1500Amps.Not quite the same, but acceptable for most uses. And at 50 cents vs 10-30 bucks for those 'real' fuses...But when working on such equipment, I'd rather want to stick with the right fuses. You reallydon't want a DMM exploding when there is a chance of probing around live circuits carrying suchvoltages and currents.

author: Bored@Work
author_rank: Super Contributor
timestamp: February 23, 2012, 11:41:43 am
content: Quote from: tamtam on February 23, 2012, 03:11:51 amTime to look for new friends.

author: Unknown
author_rank: Unknown
timestamp: February 23, 2012, 11:41:55 am
content: I actually expected the bolt belonging to these washers to be in there instead of the smaller fuse. That would have fixed that annoying blown fuse problem.Quote from: Short Circuit on February 23, 2012, 11:30:25 amWhy would a fuse with a 1 kV rating have a surge capability of 2.5 kA? Fluke specs 10 kA. The ones I have here are the same, so it's not a recent spec change.Quote from: Short Circuit on February 23, 2012, 11:30:25 amMake sure to label the instrument as 'not for mains / high energy / dangerous voltages, only for SELV'. I don't see the issue with using smaller ceramic fuses for SELV measurements, but I would be hesitant to put them in an instrument labeled 'CAT IV 600V', just because of the confusion it may cause.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: February 23, 2012, 11:57:03 am
content: Quote from: alm on February 23, 2012, 11:41:55 amYou're so right. That figure doesn't make sense at all

author: Tube_Dude
author_rank: Regular Contributor
timestamp: February 23, 2012, 02:58:35 pm
content: Hi TamtamThink positive, just bend the clips, and you have earned 4 nice washers in the process...

author: G7PSK
author_rank: Super Contributor
timestamp: February 23, 2012, 06:16:24 pm
content: Why can't these meters have a trip like they used to have on the old AVO's then there would be no problem with fuses.

author: Zero999
author_rank: Super Contributor
timestamp: February 23, 2012, 08:37:49 pm
content: Quote from: G7PSK on February 23, 2012, 06:16:24 pmBecause I doubt the breaking capacity would be anywhere near as high as the type of fuse used in a Fluke.

author: Pentium100
author_rank: Frequent Contributor
timestamp: February 24, 2012, 07:43:19 am
content: This is why you should always try to use a resettable fuse/circuit breaker instead of the regular one. Sooner or later, the fuse is going to blow, the owner, not having a spare, but needing the device working "this instant" will replace it with a piece of wire.Some time ago where I live we didn't have circuit breakers on the mains - just regular fuses - I bet at least 50% of them were replaced by wires. Now with resettable circuit breaker sthere is no need.

author: wkb
author_rank: Super Contributor
timestamp: February 24, 2012, 09:01:51 am
content: Quote from: Pentium100 on February 24, 2012, 07:43:19 amA resettable breaker with the 'break' capabilities of the fuse in the Fluke would probably be the same size as the whole Fluke itself..

author: Zero999
author_rank: Super Contributor
timestamp: February 24, 2012, 05:55:08 pm
content: Maybe they could use both?A resettable breaker with a lower tripping current than the fuse. In the case of most low current overloads the breaker will just trip and can be easily reset but when a large current causes the breaker to arc over, the fuse blows before any damage is done to either the breaker or the meter.

author: paul
author_rank: Contributor
timestamp: February 24, 2012, 08:44:56 pm
content: I found this fuse `repair` (fuses fused together?) inside a Fluke 189 at work when I replaced the batteriesno one owned upalthough it must of taken them a while to solder up.However I am glad, make that very glad, I spotted it before working on some mains equipment or a three phase supply.

author: SeanB
author_rank: Super Contributor
timestamp: February 25, 2012, 09:20:04 am
content: I had some machinery that used Diazed fuses, which are rated for 10kA breaking. Replaced with minature circuit breakers of similar rating, as I got annoyed with fuses popping randomly on switch on as they aged, and with replacements costing more than the mains rated breaker. As a bonus I got 3 phase tripping, which made things easier as a blown phase fuse could give strange faults. I later upgraded the supply side to add a 3 phase ELCB, and had to replace industrial heater elements that had developed non tripping leakage to the housings. Extra protection is always good.I did see a Fluke 77 that was used by Eishkom worker to measure a 11kV line. The fuse survived, along with the battery and the display. The inside of the case had a lovely copper coating, and a PCB that had absolutely no copper traces, except for the solder pads, in the lower section. That came in as a warranty claim.The lift at work still has Diazed fuses, and I used the spare fuses I had to replace those that had been "modified" by assorted lift mechanics if the blew, so as not to have fuses with external wire elements.

author: wkb
author_rank: Super Contributor
timestamp: February 25, 2012, 10:20:33 am
content: Quote from: paul on February 24, 2012, 08:44:56 pmNot too surprising given that these bloody fuses are typically not on stock and the absolutely ridiculous prices charged for them..I would not care working on household mains with this Fluke, there are no kA in sight there (more like 16A in systems in NL).

author: paul
author_rank: Contributor
timestamp: February 25, 2012, 07:53:47 pm
content: After watching Dave`s video of cheap meters (with glass fuses for protection) going bang I want the right fuse in my meter.I would not want that fuse protecting the meter whilst I am trying to measure something in a tight space with the meter right next to my face.This meter has been used to check three phase supplies and switch gear also logging charging voltages on 200Ah lead acid backup batteries, so if I do something dumb with the meter I hope that someone else hasn't done something dumber by `repairing` the fuse and putting it back in the cupboard for me to use.However I can understand it having to be bodged if you are desperate and dont have a replacement fuse.And you are right, Fluke fuses are expensive

author: Randall W. Lott
author_rank: Regular Contributor
timestamp: February 28, 2012, 02:53:12 am
content: At that rate, you might as well replace the fuse while measuring mains voltage. Haha, I'm just joking.