How fast are 'Fast Fuse' and how to identify?

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Hi,
wired fuses come in 3 speeds. fast, standard & slow (or time delay), the markings would be F5A, 5A, T5A.
All these are fairly slow compared to an MCB and extremely slow compared to BJT output device. Fuses rely on downstream robustness to survive the short term overload before the fuse opens. Transformers have a large amount of thermal capacity and hence lag to help them meet this overload.
The real purpose of fuses is to stop the equipment or house wiring catching fire.
 
If a fast fuse is specified, then it's best to forget the ones you have, and get some F5A ones. Look in a parts catalogue.
BTW there are ultrafast fuses designed to protect semiconductors, marked FF5A. Some industrial ones are designed to protect thyristors etc. in inverters for motor control. I'm not that sure how effective they are though, I only get to see the ones that have failed.:D
 
johnnyx said:
If a fast fuse is specified, then it's best to forget the ones you have, and get some F5A ones. Look in a parts catalogue.
BTW there are ultrafast fuses designed to protect semiconductors, marked FF5A. Some industrial ones are designed to protect thyristors etc. in inverters for motor control. I'm not that sure how effective they are though, I only get to see the ones that have failed.:D


Hey Johnny X, are you saying with the FF fuses, BJT's no longer need to protect the fuse? ;)
 
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