Not many consider it. I still have some storage heaters and the shower would be about 40% of 80A so...
As for blowing the fuse: I did that on my last GF's place. So much for the assumption of some distance from the fuse - I was inside in v. cramped place and the fuse was about a metre of wire away on t'other side of the wall. After I could see again I 'phoned for rescue and in an hour it was replaced.
Old Wylex rewirable fuse box - metal clad version. If you leave the plastic fuse cover off, there is only a short path between the supply side of the fuse and the front metal case opening. When one of the rewirable fuses blows, the arc will often end up contacting the front metal case opening, causing a much bigger arc which is protected only by the main fuse. The plastic fuse cover actually sits inside the front metal case opening, preventing this when it's fitted.
In a block of flats which all originally had these Wylex units, and many had long-since lost the plastic front covers, blown mains fuses were a regular occurance.
In another case, I have seen a main cutout operating close to its max rating, which caused all the pitch to melt and run out of the head-end connection and make a mess. It's possible a poor connection might have contributed to this too.
Your fears are unfounded. 20mm fuses behave quite diifferently to incomer fuses
NT
Fears of what exactly.... As for teh fuses they are for a lab we run. We get the studetn to undersaqtnd that even an 1.5V battery has 'power' we get them to short it out to blow a fuse. In the book we are using it states use a 3 amp car fuse. I tried that and the fuse did not blow, so a useless sort of experiment that would have proved little. So I decided to get 1 amp 'normal' for the lab fuses of 1 amp. These can be seen to blow too. Now considering a 11.5V AA (alkaline) on short circuit these batteries can supply 3.6 amps as measured, so why don't they blow a 3amp fuse ? I had a pretty good idea, students, well they are here to learn. So if they have any real interest in their results thay might just ask why a fuse rated at 3 amps doesn't blow when 3 amps are passed through it ? I intend to given them some clues, both theory and in practice.
My intention is also to get them to learn how to cut and strip a piece of wire, where as some academics prefer us to buy quantities of pre-prepared leads, i.e stripped and ready for use in a box. I believe the basics should be clearly taught & understood, a couple of years ago I felt embarressed when a final year student that had been awarded a degree in electronic engineering came up to me saying his coil wasn;t working. He had nailed a coil of enammled copper wire to a board and annouicned he didn;t know copper conducted, after he put a metal, nail through the coil. But why shoudl I worry, he'll probbly get a managment tube in a power plant. Or perhaps he'll design the next wind turbin as that was his final year project !.
This isn't a "simple" internal move of just a meter(*). It's either moving three meters (one of which is E7) to an outside box or dropping one supply and moving a normal and an E7 meter outside. The cutout would also move outside. So large outside box, suitable hole in 12 to 18" rubble stone wall, hopefully isolators for each supply inside, as the distance from meters to CU's will be well over the prescribed amount.
When various DNO engineers have looked at their side of the supply there have been "hum, that could do with replacing/upgrading". The pole transformer is quietly rusting and is, apparently, only 16 kVA. With the night storage going flat out (9 kW+) and a 10 kW shower, there isn't any head room for the 3kW kettle. Yeah I know they can take gross overloads for a number of minutes but the regulation leaves a little to be desired. The NS heating coming on creates the best part of a 10 V drop in supply. Oh and the cutout is labeled 100A = 23 kVA...
Anyway had a call from ENW today with the results of the voltage monitoring (10 min averages) Max 253 Min 228. *Just* inside the allowed range, bother. My UPS said 255 but that is a 1 min average and the voltmeter is a bit "granular". How ever I also mentioned the difficults of getting a site visit, and the nice young (well she sounded young) lady sent through a *much* simpler form, which ought to provoke a site visit. B-) She also had a reasonable technical grasp of the 33/11 kV distribution, lines, backup lines, as well.
We might be getting somewhere but she did mention a base line price of £600!
(*) If it was I'd probably pull the cut out and move it myself Seals, what seals?
I blew one a few years ago at work. I removed a cooker switch and caused a LE short. The 80A BS1361 main fuse blew but the 30A BS3060 fuse stayed intact. The 80A fuse would probably have been 30 years old.
That's quite an achievement when following safe isolation procedures :-)
Owain
Rules are there to be broken.
I think I'd rather break the "don't pull the main fuse" rule.
Owain
Surely it was the apprentice's fault? ;-)
So are fuses..... ;-)
So I did wonder why I was asked if I'd ever heard of one blowing. I assume they must do otherwise they'd be pretty useless and not used.
Of course they serve a useful purpose
I didn't ask you, my response was to Peter C who suggested that the reason for some one wanting to fit a lower value main fuse was as a way for the supply co to reduce demand.
I was just pointing out that main fuses don't normally blow, so that was an unlikely reason.
The responses here have confirmed that, since all the cases people have recounted have involved some unusual event.
Is it the fuse or the cutout that is labelled up as 80A?
I'd assume so and te4h use of a fuse is for safety nothing else.
I must have missed that point ad I'd very much doubt it would effect demand.
Yep that's what fuse's are for, blowing in an 'unusual event' mostly related to too much current being drawn and a significant amount over what would normally be expected.
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