Fuses - converting from glass fuses to modern blade fuses

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JPB
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Re: Fuses - converting from glass fuses to modern blade fuse

#11 Post by JPB » Fri Jul 17, 2015 9:08 am

History wrote:Glass fuses can be repaired by unsoldering and passing a new piece of fuse wire through the fuse.
:|
That approach is no less worrying than the idea of wrapping the fuse in some foil from a tab packet!
Buy a new fuse.
History wrote:..//..I also don't make a habit of shorting stuff out.
I don't suppose anyone does but I've lost count of how many fuses I've met that had failed because of - for a couple of examples - the extra current required by the motor to cope with wiper racks that had been packed with some sort of rainwater/old grease fudge-style mixture, then there are contact studs that overheat and become loose in their substrate in indicator stalks, headlamp switches and similar high current locations. This wasn't so well known when every stalk switch was assembled around a suitably resilient chunk of phenolic resin but these days, even the good Lucas-style switches from James Paddock are built with plastic cores and all it takes is one good drive through a dark, windy storm to create sufficient use to melt the switch and kill the fuse.
In the case of this stuff, they really don't build them like they used to.
J
"Home is where you park it", so the saying goes. That may yet come true.. :oops:

tractorman
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Re: Fuses - converting from glass fuses to modern blade fuse

#12 Post by tractorman » Fri Jul 17, 2015 10:21 am

Thanks for the timely reminder John - I have a new switch for the Land Rover as the stalk on the original turns in its housing (and has a strange bend in it). I was considering relays near the lights and have a fairly heavy cable going there (for the horn and rad fan), so its an easy job to put relays on. However, I intended to be lazy and not fit the relays I had already bought! So it's back to plan A then!

Perhaps I shouldn't say this, but I once had a job to fit 15A fuse wire to 13A fuses! We were selling Electra Beckum 3kW saw benches where I was working (in 1980) and they were popping fuses like mad, prompting lots of warranty claims. The rep pointed out that the users (mainly small building outfits) should be using 110V and not 240 machines (but we didn't sell 110V ones!) and said they had been trying to get permission to make 15A fuses to get over the initial surge (which was higher due to the lengths of some extension cables dropping supply voltage), so suggested someone should make them...

I suppose that's better than my friend's method for his stick welder - a spout bolt with the head removed! I did manage to get him to use a 15A socket with its own fuse on the dis board, but failed to get him to BUY some 16A plugs, sockets and extension cables!

I hasten to add, I don't endorse either method and have a 16A socket and extension cables for my MIG and compressor! I have no doubts the person who moves here after I go will have to do some major rewiring as it's 20 years or so since I altered the garage wiring - it's done properly, well before Part P regulations (honest guv) ;)

Interestingly, the Passat used to blow the wiper fuse on piece (sometimes two or three a day). I stripped it down,cleaned and lubricated everything and couldn't find the fault - the motor current was well below the fuse value when it started up. I replaced the fuse with a breaker of the same value and it never tripped!

The alloy in the fuse will depend on the make to a certain extent - some slow blow ones have a little "spring" coil at one end of the wire or a waist in the middle of the alloy strip.

History
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Re: Fuses - converting from glass fuses to modern blade fuse

#13 Post by History » Fri Jul 17, 2015 7:49 pm

Resoldering a glass fuse with the correct rated fuse wire is nothing like silver paper botch. All I do is use the same process that the makers of the fuse use.

A lot of modern switch gear is total rubbish.

A design of fuse I like is the glass fuse in a screwed holder I forget what they call them. I done a fuse/distribution board for a mates boat using these and the finish product looked very tidy and robust. Marine stuff is better quality.

Circuit breakers should always have a fuse in the supply to the breaker. This is because its possible under certain circumstances for the contacts to weld shut.

Bob.

tractorman
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Re: Fuses - converting from glass fuses to modern blade fuse

#14 Post by tractorman » Fri Jul 17, 2015 11:23 pm

History wrote:
Circuit breakers should always have a fuse in the supply to the breaker. This is because its possible under certain circumstances for the contacts to weld shut.

Bob.
That rather defeats the point - and cost - of fitting circuit breakers then...

Perhaps I should rip out the breakers that were in the "new" consumer unit in the house - I can get away with it as the box was fitted before Part P regs came in (they are the IEE regs that say breakers must be fitted).

History
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Re: Fuses - converting from glass fuses to modern blade fuse

#15 Post by History » Sat Jul 18, 2015 7:08 pm

If the circuit breakers in a household situation don't break then the main fuse fitted by the electric company will blow. This is why the big fuse is there. Fuses are more reliable than any circuit breaker because fuses so simple.

Bob

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JPB
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Re: Fuses - converting from glass fuses to modern blade fuse

#16 Post by JPB » Sat Jul 18, 2015 7:33 pm

I'm not certain whether you're attempting to make us laugh, if so then I apologise for not being in tune with your sense of humour. Otherwise, there's a meme for this:

Image
J
"Home is where you park it", so the saying goes. That may yet come true.. :oops:

tractorman
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Re: Fuses - converting from glass fuses to modern blade fuse

#17 Post by tractorman » Sat Jul 18, 2015 7:40 pm

No, the main fuse is to protect against massive overload and were fitted long before circuit breakers. This is one of the cases where the fuse protects the cable leading to it - not the one from it.

There were problems about fifteen years ago when 10kW power showers became popular and the DIY stores started selling them to the consumer (rather than a professional installer). Main fuses were popping like mad, even though the (uprated) breakers weren't. A former colleague had a devil of a job explaining to customers that they should have contacted the electricity company to get a larger main fuse. As far as they were concerned, if a DIY store sold them the device, it was just a matter of wiring it up (no Part P in those days, so a DIY person could do wiring in bathrooms).

On more modern houses than ours, they fit 100A main fuses; though they replace 60A ones with 100A ones as and when the smaller ones blow and ours hasn't blown - yet. I'd hate to think of the state of the 20A cables on a ring main if there was enough of a problem to blow a 100A main fuse. However, I would suspect that the RCD will trip by the time the fire starts (unless it was our older split-load system, where the lights, immersion heater and cooker aren't protected by the RCD).

I will agree that something that heats up and melts is a lot more reliable than a mechanical device, there again, until the fuse blows, there isn't a way of guaranteeing that the fuse wire will melt at, say, 13.1A rather than 12.5A even if a fuse made with the same wire blows at 13A. Though one of my least favourite jobs was to replace the internal fuses on domestic deep fat fryers (popular in the 70s) - they seemed to melt almost as soon as the oil got to working temperature and the fryer was invariably covered in old oil!


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JPB
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Re: Fuses - converting from glass fuses to modern blade fuse

#19 Post by JPB » Sun Jul 19, 2015 10:40 am

:shock: Rich, thanks for posting that copy of the Citroen C4 wiring diagram..
J
"Home is where you park it", so the saying goes. That may yet come true.. :oops:

suffolkpete
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Re: Fuses - converting from glass fuses to modern blade fuse

#20 Post by suffolkpete » Sun Jul 19, 2015 11:19 am

The rating of a fuse is its continuous rating. If you plot the current against the time to blow, you will find that the "knee" of the curve, ie when it blows more or less instantaneously, occurs at around 2.2 times the rated current for a normal fuse, although this should not be a problem if everything is dimensioned properly because it all happens too quickly for the supplying wiring to heat up. Circuit breakers are designed to have a similar characteristic.
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