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Motivation. I'm depressed - not miserable, just under-motivated - and posts frequently get rewarded by responses. My collaborator in London is away on holiday, and while I know that I ought to be getting on with building the circuit, I find myself easily distracted.

-- Bill Sloman, Nijmegen

In addition, by carefully selecting the fuses in various stages of the electric supply chain, you can selectively limit the extent of power failures due to a single point of failure.

If a single point fails, it should not cut the power from healthy circuits. By suitably selecting the fuse ratings and speeds, this can be achieved. However, one should be careful, if there are some thermal (I²t)+electromagnetic (I²) circuit breakers on the feeder side, the circuit breaker can be blown due to the I² peak, before the downstream fuse (I²t) is blown.

A fuse is not a good tool for protecting downstream equipments (motors, electronics), but some more accurate devices are usually needed.

Not always. You'd best check data sheet for any part number for continuous non-dissipative operation in the circuit in question.

RL

"All fuses are comply with the IEC standards..."

Sounds like the safe thing to do. Do you have a counterexample offhand?

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?-)

Here's a list of probably the most common parts used in North America.

marking VAC VDC 8/20 J W mfr S14K140E2 140 180 6000 55.0 0.60 Epcos P140L20 140 180 6500 75 0.6 Bournes

14D221K 140 180 6000 75 0.6 Meritek TNR14V221K 140 180 6000 55 0.6 Nipon Chemicon ERZV14D221 140 180 6000 55 - Matsushita SV140K14 140 180 8000 94 0.6 SEI Z15C221 140 180 55 0.6 Semitec TMOV15S221 140 180 10000 125 1.0 SET ROV20-221K 140 180 6500 124 1.0 TYCO

The tendency shows an ancient western/eastern split in naming conventions.

So, perhaps you can see the possibility for misidentification of operating voltage, or mis-margining.

RL

Agreed. A lot of the work in developing effective surge protection goes into selection and testing of fusible links that will not fail due to the surge event. At some threat levels, the best you can predict is n x surge level, before the fuse becomes compromised. Below a certain rated current level, this is not possible, so either surge protection has to be 'out-board', or under certain specified instances, the fuse made accessible for easy replacement.

The surge protection is supposed to do just that and the fuse has it's own job. Recent modifications to the UL1449 standard have required MOV manufacturers to requalify parts to demonstrate safe failure modes of the MOV in the event of overstress that results in thermal overload.

Even the generic dollar-store CCFL house lamp will use a 1A or 2A 'normal blow' fuse, if a nickel-film resistor isn't used instead, for double-duty inrush and fusing purposes. These are 15 and 25W devices with usually less than 22uF capacitive storage, for use under limited line voltage range in the domestic low-surge exposure environment ...........and you know how long they're 'expected' to last. In my experience, the fuses used here do their job.

RL

Epcos S20K250 - 250Vrms, varistor voltage 390. Marked with RMS voltage

Panasonic ERZV20D391 - 250Vrms, varistor voltage 390. Marked with varistor voltage.

Specifying a Panasonic "240V" MOV will get you 150Vrms.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

I'd second that. Different manufacturers have different conventions.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

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"Graham Stevenson, Sole Proprietor at Graham Stevenson Electronics, St Albans, United Kingdom".

He must have started getting more work.

-- Bill Sloman, Nijmegen

Yeah. Bloody nuisance, isn't it ...work?

I'm taking an advanced retirement day, waiting for an eight-to-fourer to call. Never give these guys the choice of 'anytime convenient' - they'll choose to pick the entire day........

RL

"All your fuse are belong to us"