(An ambient temperature derating curve also appears on page 3.) Note that the curves slope straight up on the left side, an asymptote as current approaches the rating (or, somewhat above it). Mind that it is only a typical curve - real parts will have min/max some distance around the ideal curve (the datasheet might show this, too).Įxample: Bussmann ATC blade fuses datasheet The current-time trade off is given by the time curve of the fuse. For example, it may open faster / at lower currents, at higher temperature - indeed, thermal fuses are optimized to encourage this effect their current ratings do indeed depend on temperature. They will detail exactly when the fuse is, and isn't, supposed to open, and other conditions which may affect it. Of course, exact ratings may vary - consult the datasheet. (A typical residential circuit might be rated say 10A, but might deliver several thousands of amperes into a fault.) The fuse only opens rapidly when the overload is extreme (fault conditions: short circuit current flow), 10s or 100s of times nominal. A typical fuse might take some minutes to open at 50% overload, and some seconds at 100-200% overload. In fact, fuses are rated to open at several times the rated current - and, this takes some time to happen. for some particular piece of equipment? With so many to choose from, they must be pretty precise (~10%), right?!Ī fuse is rated for a nominal current, for which it will never open, within ratings (ambient temperature, etc.).Ī fuse is NOT rated to open at some tiny increment above that current. Consider the range of ratings offered: do we really need 6.3, 8, 9, 10, 12A, etc. It's a common misconception, I think - and not at all an unreasonable one. I think this arises from an overestimated confidence in what a fuse actually does, how it works. We need more information to determine where exactly. Thus, without knowing anything else about them, two 10A fuses in parallel might have a combined rating somewhere between 10 and 20A. ![]() (If the currents do end up sharing perfectly, the rating will be exactly the total.) The fusing current will be less than or equal to the combined sum of current ratings.(Unless the resistance in parallel with it is infinite, it will not be carrying exactly the full current.) The fusing current will be higher than the highest single fuse in the combination.Without resistance being known, the only thing that can be concluded is this: If we know the resistances, we can know the current division, and thus how close two (well-defined) fuses are to opening, under some applied current. A fuse opens when its rated current has been exceeded, for some duration of time. The equivalent circuit here is two resistors in parallel, with some load current flowing through the combination. There are two issues with the question: it's too generic, and not very applicableįirst I will explain the problems with the question, then provide an answer comprehensive enough that one can figure out the answer for their particular case.We cannot accept responsibility for returned parcels which are undelivered, please retain your proof of postage etc., you may require it on the event of a claim with your carrier.The currently existing answers to this question aren't very good.Please help us to help you by completing the relevant returns form. All returns are to be accompanied by the senders name and address, account number, order reference number (these are found on the invoice), and reason for return.We cannot accept any items which have been specially ordered for you or manufactured to your specification for return.(We reserve the right to levy a charge to replace product packaging which is damaged or defaced). Items are returned complete with all packaging in good condition.Items should be returned unused in their original condition in order to secure a refund.Items are received in a resalable condition.Goods which prove unsuitable may be returned for refund if they are returned to ourselves within 14 days of receipt.
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