Fuses In Household Application

What is this "600v" representing? What rating is it?

http://www.electronicsforu.com/EFYLinux/efyhome/cover/sep2004/PolyFuse.pdf

http://en.wikipedia.org/wiki/Resettable_fuse

I'm talking about this fuse.

Can we replace main fuse(rewirable fuse/mcb) we use near energy meter in our household by this polyfuse? If not, then why?

redfred,

I want to clear my doubts. Thanks for helping me.

On considering a fuse, what all are its ratings?

What are the ratings of a conventional rewirable fuse/mcb we use in electrical circuit?

This figure shows "600V". The what is this voltage value indicating?

I've seen Bournes' advertise a Poly-fuse with a 60V level previously. I suspect that this has a typographic error of an additional zero. At the same time, maybe Bournes does have Poly-fuses that can handle such high voltages. I would need to do a lot of my own testing first to put this onto line voltage with my name, reputation and other people's lives on the line.

What are major applications,ratings,Limitations etc. of Polyfuse ?

Really!?!? You don't grasp the method of how to discern the applications, ratings, limitations, etc. from any manufacturer's data sheet. Well let me start with one of your unstated criteria, the advantages.

The advantages of a product will be the selling points of the product. These attributes will be at least 75% of any sales brochure. The quality of these attributes will often be the discerning difference between one manufacturer's product and another. Very often a company salesman will only know these attributes but a sales engineer will have a better grasp of the entire product.

The applications are usually a very easy to discern attribute for a product. The already known applications can be found in the manufacturer's reference database under....... applications. Every manufacturer wants their products to be used in this mode for this is the modality this product was design to operate. Use of this product in this mode will improve "good will" between supplier and designer as the product performs the designed job. This does not mean though that this is the only modality that a part can be successfully used. To find new modes requires how to discern the last two attributes in your list.

The limitations of a part can also be considered the drawback of that part when a system designer inadvertently exceeds the parts ratings. The ratings thus contain the advantages and limitations of a part. This is where a sales engineer (or application engineer) instead of a salesman can be helpful for they know what the part can and cannot do. The ratings of any part are what your engineer will be looking over to decide which part will work in your system.

Now to discuss a Poly-fuse application specifically, these protection devices do have many useful applications that work well. One scenario is in a daughter board and peripheral designs of a system, where the main system must continue to run even if the peripheral has a catastrophic failure that might self recover. Think about an external USB hub that might have a piece of aluminum foil (gum wrapper on a messy desk) accidentally shorting out the primary +5V supply. You certainly do not want the current protection of the computer's main supply limiting the current. This can cause the whole computer to crash at an unknown moment that can destroy critical data. However, placing a traditional fuse between USB output power and computer main will protect the computer but one brief accidental short circuit will render the the USB output useless until the fuse gets repaired.

All of this entire scenario will be obvious to a true electrical engineer. You need to hire one for your project. You do not have to hire an engineer full time, you might consider hiring one as a consultant for just your one project that needs proper circuit protection.

Can we use Polyfuse in both AC and DC circuits? Is there any specifications for it?

If you do not understand what the manufacturer's data sheet and application guide says, then you are not qualified to use this.

Let me put this in easier terms for you. Many people here have given you good advice. You either refuse to take the advice or are incapable of understanding the advice. Why do you come back?

Redfred, I don't who or why your posts 21 and 27 were voted OT, they were well thought out and understandable in the English language and dead on the subject matter. It's to bad that the OP can not grasp and heed the warnings that you have made so clear about the dangers involved. I guess it's like the old saying goes, "You can lead a horse to water but..." Anyhow, I gave you GA's on both, hopefully the OP has enough sense the listen. DJ

You really need to see the aftermath of a properly rated fuse in a 480volt system that blew under max. current draw and the instantaneous arc that developed, arcing from the incoming mains-jumping 1.5 inches to the metal frame work. It charred and melted everything in the surrounding area!! Not pretty. And sure as hell wasn't fun repair it either. Then, I think you would appreciate the safety of using the Properly Rated Fuse for Both Voltage and Current! DJ

The component you have mentioned is meant for over Voltage protection in electronic circuit. It works just like Zenor diode but it is applicable for AC circuits protection only. it Is called metal oxide Varistor (MOV) it is also Know as VDR & It is a surge suppressor having non linear VI characteristics. the voltage value indicates the component maximum with standing voltage. this component is generally connected in parallel to supply and load

Sorry but you are very wrong here. A poly-fuse is a very different component than a MOV or zener diode. A poly-fuse is in series with the load while a zener diode is parallel to the load.

Fuse and circuit breaker ratings encompass 1) current, 2) maximum allowable voltage, and 3) short circuit interrupting capacity. All three criteria need to be satisfied.

yes i was mistaken. I would like to add some more points These are not fuses but polymeric positive temperature co-efficient thermostats. These are made by combination of carbon and Polymer. The current range of the component varies according to combination ratio of carbon and Polymer.

It would be unwise if at all possible, as these type of fuses reset after a short time & if the reason for the tripping were not found then the power would be restored & either become unsafe or the tripping sequence starting again.

Ok. Thanks for giving information.

I found only a little information about Polyfuse on the net.

Can anyone give more information about Polyfuse. What are its major applications,ratings,Limitations etc.

Help...

Thermal cutoff - Wikipedia, the free…

Then go to a supplier web site and do some research. I'm fresh out of injectable polyfuse knowledge.

Then hire an electrician.

Poly-fuse is a brand name for PPTC (Polymeric Positive Temperature Coefficient Device), also commonly known as a resettable fuse (which is misleading as they do not break the electrical circuit, just limit the current).

Link

These are suitable for extra low voltage DC applications such as DC power supply protection, extra low voltage AC applications like speaker protection.

These are NOT suitable as house fuse replacements, either in practice or in any electrical standards or regulations I am aware of. They have nether the disconnection ability or fault current handling ability of a fuse or a miniature circuit breaker.

Link

What are the limitations and advantages of a PolyFuse ?

It depends on the application, but one of the overall advantages is it is a self-resetting current limiting device that operates quite differently to a fuse or circuit breaker.

The overall disadvantage it has (in many applications) is it limits current when it heats up but allows the current to flow when it cools (not always a good thing), also it has a low current rating (unlike a fuse or circuit breaker) and its operating heat can be a problem if not carefully managed.

Again, all application related, and some disadvantages are actually advantages in the right application. Think of it not as a fuse but as a temperature controlled variable resistor.

As I have already said in post #17, for the basics look on Wikipedia and try a Google search of "littlefuse polyfuse" or "polymeric positive temperature coefficient device" or PPTC for more general datasheet and application notes.

The latest edition of British Standard 7671 requires the use of resettable circuit breakers. Older installations have fuses and, while obsolete, there is no requirement to replace distribution boards unless new circuits are being run.

If in doubt, consult a qualified electrician locally.

Jobinhere,

I hope you take the answers you have received and use them to further your education. I am glad to see your follow-up posts also.

As I understand it, the "polyfuse" has one function--to temporarily limit the current during an overload condition. It does not interrupt the current and is not designed to provide any protection during a "short-circuit". This current limitation is by a physical change to the polyfuse's matrix--the heating expands the polymer to separate the conductive graphite particles and thus increase the resistance. This therefore limits the current in a way that is proportional to the amount of current trying to flow through the circuit. The fuse will have a characteristic curve of temperature rise and current flow. Its voltage rating is simply the maximum voltage that can be safely applied across the leads without a short-circuit being created between the two leads.

A traditional fuse has one (but usually several) metal components that have a fairly low melting point. As the current increases, it will create heat. At some point in time, the metal will melt or vaporize and cut off further current flow. The voltage rating is the maximum voltage that the fuse can safely interrupt. If the overload is fairly modest, the fuse can get fairly hot, but its resistance changes only slightly. Therefore the fuse is not limiting current. Instead it is cutting it off at a preset point. If the overload is very severe, the fuse will act quite quickly. In these conditions (much faster action than a polyfuse can every attain), the traditional fuse will effectively limit the current flow to a value that is safe for the equipment being protected.

A large variety of fuse types exist; designed for different voltages, currents, current limits, time delays, etc. Look at the manufacturers' literature for information about why different ones are selected. Look to the different codes for requirements that have to be met (and thus which fuses may or may not be selected).

A fuse will interrupt the current; a polyfuse will not. A fuse has a known interrupting rating (the short circuit current it can interrupt without an explosion); a plolyfuse will explode in a short circuit.

--JMM

Can we use Polyfuse in both AC and DC circuits? Is there any specifications for it?

Can we use Polyfuse in both AC and DC circuits? Is there any specifications for it?