UL Class CC Fuse

Your concept looks sound, and I like the spring loading and symmetry. I don't know what a listing lab could "throw at it" to try to make it fail.

Thanks, makes me feel better. i sure hope that the UL standard does not prohibit it. Frankly, i can't afford the $1000 that the document costs

I like te concept, but what's going to prevent me (a gorilla) from putting a non-rejection type fuse in there and just jamming it in by spreading the two clips apart a little?

Excellent point! Thank you.

How about i make this rejection more rigid ? Like this perhaps....

This will be brass or phosphor-bronze. Maybe even beryllium copper if the traffic will bear. If these are still weak in your opinion, i can give this rejection projection (ah, poetry!) in the spring-steel clip.

What do you think ?

Why would you say that? He said in the beginning that he is re-designing a product for production and want's to improve it. Is there any harm in improving on an existing design? Or perhaps you think we should all continue using everything that exists exactly as it is now and never change anything? That my friend is called "stagnation".

Just to clarify, the existing design is also mine. i made it for my client in North India. No rocket science, just a compact, good-looking and good-performing IEC switch. A couple of patentable points, client is considering whether to patent.

Thanks for the defence, but you are wasting your breath on this heckler.

kvsridhar

I think maybe you are still missing the point. The point of the rejection tip on the fuse is that the corresponding clip "demands" it and non-rejection type fuses, i.e. those without the protrusion, will not make contact and will not be able to complete the circuit, rendering them impossible to use.

So the clip must be EXCLUSIONARY of all but the fuses WITH the protrusion. Your clip is INCLUSIVE of the rejection fuses, but is not EXCLUSIONARY of the non-rejection type. I could take a non-rejection type fuse, place it in the clip and it will still be making contact with the current carrying components.

i assumed that the contact is made on the main spring clips. And the constricted part is to prevent entry of a fuse which does not have the smaller 'nipple' of the CC fuse. i am under the impression that the lower capacity fuses have a FULL LENGTH end ferrule, which will be blocked by the smaller portion.....i got this impression from another fuse, not CC...

i could be wrong, i have to consult some friends in UL. "What is the fuse that should be rejected by the switch" is a question that i should be asking...thanks for the comment.

i have checked with Cooper-Bussmann and Littelfuse catalogs, and this is one rejection i could find....CC vs Midget fuse...

Midget fuse, same size as CC, but without the 'nipple', 600V but 10kA capacity usually (one type even has 100kA, but not good enough as per UL). The full ferrule at the top cannot enter the preventor as i have proposed.

This rejection is achieved i think. Have to ask customers what else must be excluded, if any.

In your first design, imagine that someone tries to insert a non-R fuse. The bent-over portion of the clip is supposed to prevent this, but with enough force the fuse could (maybe) spread the clip far enough for the full diameter to squeeze between. Perhaps the gray "backup spring" is rigid enough to stop this?

Having worked with industrial electricians for over 30 years, I know one definite fact, they can force anything to fit

The back up spring may not be needed if i decide to use phosphor-bronze or beryllium copper. i made the provision anyway, since i may end up using brass + spring steel clip.

Yes, it may then be strong enough to resist normal insertion force. But won't be 'gorilla'-proof. So i am thinking of the alternatives.

Thanks for your inputs.

I suppose the question is "how far will a professional lab gorilla go to defeat your system?" In this case, one could envision a piece of 10-mm copper tube ~35mm long being inserted as a "fuse."

I went to work on a crusher unit in a small gravel pit, complaint of burning up conveyor motors..... on arrival i found 225Kva Cat gen set no ground rod (or any other for that matter) a very shaky connection point from gen set consisting of a bunch of 10/4 SO cord twisted together and almost all the fuses in the disconnects for the conveyor motors ,and i mean this literally, wrapped in alum foil..... the explanation for this involved lots of shrugging and shuffling.... the best part was not only the alum foil but the three pieces of 10/4 twisted to a piece of1/4 SO to feed the 100hp motor running the crusher..... God watches out for the victims of IDIOTS..... mostly.... Oh and I almost forgot this is on a unit that is sitting on the ground with natural springs bubbling up through the framework just for that extra conductivity effect....

i know exactly what you mean. There was a horrendous accident in the 70's when some callous electricians had driven a 6" steel nail through a blown fuse. (Why? Money of course. The cost of a new fuse ≈ $25. The electrician charged $75 and put the nails through 'em). 11kV fuses, three of them in an old oil-filled fuse switch. There were 16 people in the neighbourhood when it was closed on to a dead short-circuit. The switch exploded due to 25 gallons of burning oil and sad to say, no survivors.What a tragedy that was.....

Regards.

In our setup a qualified Engineer got 300A Copper braid soldered inside an NH Fuse 300A Semiconductor grade.

Nothig un-expected.

Hi kvsridhar,

In your initial post you stated;

• "These come with a "rejection" feature (to prevent fuses of lesser capacity being used), so my switch will have to have that."

Or in other words it would prevent you from installing a fuse that had a lower rating but would allow a fuse with a higher rating to be installed.

To me this seems to be the wrong way round and potentially dangerous as it would allow the installation of a fuse with a higher rating and this pretty much defeats the purpose of having the fuse there in the first place

On the other hand if it were the other way around and prevented fuses with higher ratings from being installed it would allow a lower rated fuse to be installed which would blow sooner rather than later and therefore still protect the circuit from being overloaded.

Sorry if my statement has been ambiguous. The UL rejection feature is to prevent an inferior fuse (less rated voltage, less short-circuit capacity) being fitted in a switch meant to take a superior fuse (600V rated, 200 kA sc capacity). As i mention in another post, the rejected fuse, "Midget", has less SC capacity, and must not be used on circuits capable of delivering 200kA short circuit. Both are 30A fuses, and measure 1.5" long x 0.41" dia. Please see the images i have provided in that post...

Have i made myself clearer now? Please respond, thank you.

Ok, now I know what you mean.

There are two different issues being considered.
First is the nominal fuse rating, such as 1,3,6,10,15,20,25, or 30 A.
Second is the short-circuit interrupting capability, such as 100,000 or 200,000 A.
The rejection-type fuses (and corresponding fuse blocks) are based on #2.

If you look, carefully, at the fuse holder, you will see that the ferrel end is contacted on the end of the fuse (rejection feature #1)

The distance between the contacts is set, so that a inferior fuse can not make a circuit between the two contacts.

Yor design is feasable provided the circuit is completed on the ferrel end, and not on the cap (clip). The circuit completion, through the ferrel end, and not the cap, defeats the "gortlla" concept. The only problem I see is coming very close to patent infringement. Complete your design and talk to a patent attorney. The cost is more; however, the benefits outweigh the cost of an infringement case.

The question you have to ask yourself, and no one can answer it for you is, "Will the market support my design?" Your design may be perfect, and costly. Good enough gets the contract.

Free advice is worth exactly what you pay for.

Thank you for your comments.

However, since my original post, i have discovered that contacting on the cap using the spring clip is not prohibited. There are at least two European designs for CC fuses that i have now discovered, which use contact clips somewhat similar to my proposal. Also, the UL Class J fuse holders use such spring clips which contact on the diameter of the cap and not on the end.

Regards all.

Really a ***** discussion as a new design or improving the existing design.

I had also worked on such a project [ yes you may call it] where the demand was to minimising "GO"time of failed UPS to bring it within back-up time.

Solution was found in changing the type of fuse from UL Screwed-On to Push-On

All comments realise that CR4 have a good collection of Thinkers as well.

GA to all

Thank you all friends for your help, please keep your remarks coming ...

Where am i at this point ?

1. Is it permissible to make contact on the periphery of the end caps, as opposed to the end faces (as in the patent image) ? Yes, see the designs of Ferraz-Socomec and ABB (Stromberg). And many fuse bases for Class J fuses.

2. What are the fuses that must not be allowed ? Midget, J.

3. Is the rejection feature gorilla-proof ? Not yet, must follow up on new clip design using some FEA and then actual testing on different materials, PhBr, CuBe, Spring steel.

Thanks again, and as i said, more comments eagerly awaited.

A "J" fuse is so much bigger than a "CC" fuse that rejecting it should be no problem. The whole game here will be to reject non-R miniature fuses. The "fork" or whatever surrounds the "button" should probably be rigid. In general, barrel contact seems to make better sense than end contact, but I don't know for sure. (Just some ideas.)

i have been having some correspondence with Cooper-Bussmann on this the last few days. i was pleasantly surprised that i got very prompt responses despite the holidays.

Information provided by C-B :

1. The rejection feature must mainly address the Midget fuse and the French fuse of the same dimension. All other cylindrical fuses are either too small or too big.

2. There is no objection by UL whether the contact is on the face (as in the Cooper patent) or on the barrel (as i intend to do)

3. The CC fuse is meant to be assembled only one way (not invertable), so i must provide the rejection feature only on one side, the bottom.

This is wonderful. Thank you all for your valuable inputs and especially to tornado and Jraef who made me sit up, think and refine my design.