Fluke 77 Fuse- Bussman KTK-15- Counterfeit?

[RobertM64]

Ordered replacement from Amazon.  Pic shows what I received (left) and the original fuse from the unit.  Important differences.  The Amazon one has a black and white label, the original is maroon and white.  The Amazon one does not have the multiple crimps on the caps.  Has only 3 vs. about 20 for the original.  The Amazon one is shiny vs the matt for the original (sign of a counterfeit per the Bussmann site). Weights are 7.83g for the Amazon and 7.43 grams for the original.  Original listing photo for the Amazon fuse is actually a picture of the original, not what was received.  Cost of received: $6.  Dozens of listings for the fuse on Amazon at $6-$10 show a picture of the original.  Suspect they send out the same as I received.  I'm guessing knowledgeable folk are already aware of this.  I have already put in for a return and would like to make sure I order a real one.   But digikey and mouser have this fuse at $28, which I am just not willing to pay.  So, what should I do?

[floobydust]

Hold it to your ear and shake it, it must be sand-filled for the high interrupt 100kA rating. I think that's the reason they are normally super expensive. Fakes are full of air. You can also weigh them as you did.
The end-cap crimp is not fluted, so I would be suspicious of them being counterfeit.
It's likely a 15A fuse but not trustworthy in Cat. III or Cat. IV environments.

Sometimes electrical suppliers sell these for a much lower price. I would try those local distributors instead of electronics types.

[WattsThat]

So, what should I do?

Buy electrical parts from an electrical products distributor, not an electronics distributor.

Can be found online for less than $10 from industrial electrical houses. It’s $15 if you buy from a convenience distributor like Grainger or similar. MSC is only $12. But of course there’s shipping.
 

[RobertM64]

Ordered from Witronics for $6.99, will see what happens.

[wraper]

Marking on the picture in it's datasheet is exactly like what you received. Marking like on your old fuse was discontinued a long time ago. It would be either counterfeit or super old stock if the fuse you received looked like original one.
http://www.farnell.com/datasheets/2079436.pdf?_ga=2.179835116.939436388.1598389001-1112704206.1581825782

Pictures of Bussmann fuse on RS website has similar crimping stile as your fuse.

[wraper]

I have already put in for a return and would like to make sure I order a real one.

How about asking question first and waiting a day or two for answers? If another fuse you ordered will be genuine, it will look exactly the same.

[bdunham7]

The company's actual datasheet and two reliable sources show the current product to be similar to, but not the same as what you got.  Also much different than your original, so the design has been updated--so the fakes are updated too.  I've purchased from Witonics and the products absolutely appeared genuine--and they have a much more prominent profile than you'd expect from a counterfeiter--so I think they are probably OK.  I suppose you never know for sure.

http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/product-datasheets-a/Bus_Ele_DS_1011_KTK.pdf

https://www.newark.com/eaton-bussmann-series/ktk-15/fuse-15a-600v-fast-acting/dp/63R7755

https://www.grainger.com/product/BUSSMANN-Fuse-4XC43

[wraper]

The company's actual datasheet and two reliable sources show the current product to be similar to, but not the same as what you got.

Marking is 100% the same, crimping of the caps certainly exists on genuine bussmann fuses. Very likely it depends on production line it was produced at. No 100% guarantee that is's genuine, but there is no suspect in it's appearance.

[Fungus]

Hold it to your ear and shake it, it must be sand-filled for the high interrupt 100kA rating. I think that's the reason they are normally super expensive.

Yeah, sand is sooooo expensive.

[floobydust]

lol, let me know how you assemble them and get the magic sand inside for cheap.

P.S. Asked Eaton WTF their Bussman fuse costs $38 CDN We'll see what they say.
 

[wraper]

P.S. Asked Eaton WTF their Bussman fuse costs $38 CDN We'll see what they say.

Ask distributors. Say at Conrad (Germany) KTK-15 costs $12 at qty of 1.

[bdunham7]

P.S. Asked Eaton WTF their Bussman fuse costs $38 CDN We'll see what they say.

Because some of their distributors have customers that are not price sensitive for lower cost, low volume items.  Witonics will sell you one KTK-15 fuse,  card-packaged and shipped for $6.99 on Amazon, so perhaps they make a buck?  Mouser will sell it to you for $28 + 7.99 shipping if that's all you order--and they make 25 or 30 bucks on the deal.  They've figured out that they'll likely sell about the same number at either price, so why not make 3000% more money?

https://www.amazon.com/Cooper-Bussmann-BP-KTK-15-Acting/dp/B000BPNM54/ref=sr_1_9?dchild=1&keywords=ktk-15&qid=1598459381&sr=8-9

[joeqsmith]

I recently pulled a PCB from the trash for a Fluke 7x.  Besides a quick power on and test, I haven't done anything with it.   The meter has two fuses.  A large HRC fuse that was missing and a smaller one which appears original.   On the PCB, the larger is marked 3A 600V, the smaller 0.63A. 

These two fuses are in series with the low current input.  Looking at pictures of the 77, they had a version with an unfused 10A input.  This appears to be what I found. 

I wonder what drove them to use two fuses in series.

[bdunham7]

I wonder what drove them to use two fuses in series.

8840A/8842A bench meters are the same way--they have a 2A current range with a 2A external fuse and an internal 3A HRC fuse in series.  This makes perfect sense and everyone ought to do it--the HRC fuse is just there in case of a high energy disaster, for the normal overload the external $0.05 fuse can take the hit.

You can get probes from Cal-Test that are fused, or you can add inline fuses holders for non-CAT type (CAT 0?) situations.  There's no point in blowing a $20 HRC fuse with a 9 volt battery.

[Fungus]

I wonder what drove them to use two fuses in series.

I have a Fluke 37 that has two fuses in series on the low amps range. One is a big 2A HRC fuse, the other is a cheap 600mA glass fuse. I think the idea is that the cheap glass fuse saves the expensive HRC fuse from the little mistakes, eg. measuring low voltages with the cable in the mA socket.

The HRC fuse only comes into play when you make the BIG mistakes.

[joeqsmith]

I wonder what drove them to use two fuses in series.

8840A/8842A bench meters are the same way--they have a 2A current range with a 2A external fuse and an internal 3A HRC fuse in series.  This makes perfect sense and everyone ought to do it--the HRC fuse is just there in case of a high energy disaster, for the normal overload the external $0.05 fuse can take the hit.

You can get probes from Cal-Test that are fused, or you can add inline fuses holders for non-CAT type (CAT 0?) situations.  There's no point in blowing a $20 HRC fuse with a 9 volt battery.

Let's assume that the 630mA fuse could flash over with the 300mA fuse they used (glass filled) and the solution for arc flash was to add the second fuse.   Why go to the trouble but don't address the 10A input?   Looking at pictures of a complete meter, it doesn't appear they used additional fuses in the leads that were shipped with it.   Did they have to kill a few people before they figured out both would require HRC fuses?   

[bdunham7]

Why go to the trouble but don't address the 10A input?   Looking at pictures of a complete meter, it doesn't appear they used additional fuses in the leads that were shipped with it.   Did they have to kill a few people before they figured out both would require HRC fuses?

I doubt anyone died.  Is the original Fluke 77 CAT IV rated?  Perhaps on the 10A range they are counting on your panel circuit breaker for the high energy interrupt. 

I've seen the results of cheap DMMs with unfused 10A ranges getting plugged into the wall and AFAIK it hasn't been a big deal.  Blows the end off the tip, blows the PCB traces off the circuit board and trips the breaker, in that order.  DMM and wall socket are toast, nobody dies.  It would be interesting to see that same scene played out with a bigger breaker, like >100A.

[Fungus]

lol, let me know how you assemble them and get the magic sand inside for cheap.

The same way you get the wire inside. 

(and if you're in China making fake fuses you get somebody to sit there with a little funnel)

[joeqsmith]

Why go to the trouble but don't address the 10A input?   Looking at pictures of a complete meter, it doesn't appear they used additional fuses in the leads that were shipped with it.   Did they have to kill a few people before they figured out both would require HRC fuses?

I doubt anyone died.  Is the original Fluke 77 CAT IV rated?  Perhaps on the 10A range they are counting on your panel circuit breaker for the high energy interrupt. 

I've seen the results of cheap DMMs with unfused 10A ranges getting plugged into the wall and AFAIK it hasn't been a big deal.  Blows the end off the tip, blows the PCB traces off the circuit board and trips the breaker, in that order.  DMM and wall socket are toast, nobody dies.  It would be interesting to see that same scene played out with a bigger breaker, like >100A.

Let's assume that it was no big deal.  If they felt worse case, it would be shunted across a CAT II outlet and that the homes circuit breaker was good enough,  why wouldn't this be true for both inputs?   Why install a large HRC fuse at all? 

What's really odd is we fast forward to the next revision of  the 77 with the fused 10A input.  Again we see only two fuses, one large, one small.  The large is now used for the 10A and the small is still there for the 300mA input.   The still call out a 630mA 250V fuse but have upped the large fuse to 15A 600V.   What ever drove them to add the large HRC fuse in series is no longer a concern.

It does seem like there is a story behind this. 

A bit of a search,  a member had uploaded their manual for the meter. 
https://www.eevblog.com/forum/testgear/fluke-77-strange-demise/

*****
Note the warnings added to the manual between the two versions.   With the later revision, for safety they reference IEC 348, ANSI/ISA-S82, UL1244 and CSA C22.2 No. 231.   
*****
Also, I have a flavor of that old Limitron fuse.  Slightly different crimp and label.   These are old enough to be rated for 600V AC only at 100KA unlike what we see today with additional DC ratings.   

[wraper]

Here is KTK-30 on RS components website which looks like the fuse in question https://uk.rs-online.com/web/p/cartridge-fuses/4588582/

[bdunham7]

Let's assume that it was no big deal.  If they felt worse case, it would be shunted across a CAT II outlet and that the homes circuit breaker was good enough,  why wouldn't this be true for both inputs?   Why install a large HRC fuse at all? 

What's really odd is we fast forward to the next revision of  the 77 with the fused 10A input.  Again we see only two fuses, one large, one small.  The large is now used for the 10A and the small is still there for the 300mA input.   The still call out a 630mA 250V fuse but have upped the large fuse to 15A 600V.   What ever drove them to add the large HRC fuse in series is no longer a concern.

I'm just speculating of course, but the 10A shunt and wiring would be stout enough to trip the breaker whereas the low current circuit might form an arc for a while at a current insufficient to trip.  If you are going to short a wall socket, short it good!

As for Fluke's historical design choices, no idea.  The 8840A/8842A meters only have a 2A input, current really isn't their thing.  A lot of these were sold to the government, perhaps there is a MIL spec involved? 

I have a 1996 Fluke test tools catalog and it lists the following under 'fuse information' for models 21/23/75/77:

P/N 871173: 630mA 250V fuse in series with either P/N 871202:3A 600V fuse or fusible resistor, R20--DO NOT SUBSTITUTE FOR R20.
P/N 892583: 15A 600V fuse.  Also recommended replacement for units with a fused 10A input using a 20A fuse.

So it seems their intent is to provide fusing sufficient to interrupt 600 volts without any specific mention of current interrupt or CAT ratings.  No specs on R20.

[joeqsmith]

Let's assume that it was no big deal.  If they felt worse case, it would be shunted across a CAT II outlet and that the homes circuit breaker was good enough,  why wouldn't this be true for both inputs?   Why install a large HRC fuse at all? 

What's really odd is we fast forward to the next revision of  the 77 with the fused 10A input.  Again we see only two fuses, one large, one small.  The large is now used for the 10A and the small is still there for the 300mA input.   The still call out a 630mA 250V fuse but have upped the large fuse to 15A 600V.   What ever drove them to add the large HRC fuse in series is no longer a concern.

I'm just speculating of course, but the 10A shunt and wiring would be stout enough to trip the breaker whereas the low current circuit might form an arc for a while at a current insufficient to trip.  If you are going to short a wall socket, short it good!

As for Fluke's historical design choices, no idea.  The 8840A/8842A meters only have a 2A input, current really isn't their thing.  A lot of these were sold to the government, perhaps there is a MIL spec involved? 

I have a 1996 Fluke test tools catalog and it lists the following under 'fuse information' for models 21/23/75/77:

P/N 871173: 630mA 250V fuse in series with either P/N 871202:3A 600V fuse or fusible resistor, R20--DO NOT SUBSTITUTE FOR R20.
P/N 892583: 15A 600V fuse.  Also recommended replacement for units with a fused 10A input using a 20A fuse.

So it seems their intent is to provide fusing sufficient to interrupt 600 volts without any specific mention of current interrupt or CAT ratings.  No specs on R20.

Obviously none of us can answer why unless we were on the team when it happened.  All we can do is look at the clues left behind.   For household wiring, that small filled fuse should have been fine.  The 100KA fault current fuse would be for something far beyond what we would see in a typical home.   I imagine their own test lab was evolving along with the standards.  Maybe with the unfused 10A, they couldn't create enough energy to open it up where the smaller fuse came apart.  If that were the case, it doesn't explain why the larger fuse in the low current path was removed in the next revision. 

It looks to me like they screwed up and somehow no one caught it until the next revision.  Maybe Fluke was expanding beyond what they were able to manage. 

Looking at the smaller fuse that was in the meter when I found it, it doesn't appear to be stock as it was marked 500mA.   Looks like they were smart enough to at least get something filled to substitute it. 

Also shown is that old Limitron KTK-15 fuse I mentioned.   Notice how the label is slightly shorter and the crimp is different than what was shown by the OP.   

[bdunham7]

If that were the case, it doesn't explain why the larger fuse in the low current path was removed in the next revision.

I was thinking that the 'R20 fusible resistor' was the additional protection for the low current path, although I have no idea what 'R20' is.

[bd139]

Wish I hadn't tripped over this thread. Just bought a KTK-15 for my new Fluke 25 from here which is "assuredly genuine": https://www.ebay.co.uk/itm/153138398750 ... Fingers crossed. 

Either way it'll be better than the previous owner's ID-10T fuse that was in it (and yes the fuse is soldered into the fuse clips as well) 



(the entire analogue board on this particular DMM has been scrapped for ref as the bottom switch wafer was also melted, I assume after the fuck-knuckle did that)

[joeqsmith]

If that were the case, it doesn't explain why the larger fuse in the low current path was removed in the next revision.

I was thinking that the 'R20 fusible resistor' was the additional protection for the low current path, although I have no idea what 'R20' is.

If the fusible resistor was cheaper, smaller and met their safety requirements, it makes you wonder why they didn't start out adopting this approach.   It looks like when they first made this change, the body size for F1 also increased.  Then in the later revision it seems like it's back to a smaller 5x20mm package.   Maybe just the hand drawings are not accurate.  I wasn't able to find part numbers for that larger fuse listed. 

It's interesting to see R1, the 1K fusible resistor in series with the sparkgap on the 77.   It appears the manual is 1984.    My first Fluke doesn't have such things and as a result, I damaged the meter a few times in the lab with some very low energy circuits.  They must have been learning the basics of how to make a more robust product back then.