the 60 am Supplier main Fuse blow up

[Zehroni]

the 60amp Supplier main Fuse blow up last night. called the local national grid, an engineer came around and replace it with 63A. I was rather surprised as to why this had happened. I asked the engineer who said it was overload. we only have the washing Machin, couple of laptops, the kettle few lights and hair dryer. is that too much for 60A to blow? we had much more load than that in the past but the fuse did not blow.
is truly the load or dose the age of the fuse contributed to that.

 

[flameport]

washing Machin, couple of laptops, the kettle few lights and hair dryer.

Those would be nowhere near 60A.

Fuses can fail if they are repeatedly loaded near or just above their maximum rating, but that could take years or even decades.

Another failure would be if there was a short circuit fault in the installation, and you have old rewireable fuses which are much slower to react than a cartridge fuse.

 

[Murdochcat]

Cartridge fuses can and do just fail - it’s rare but I’ve come across it on a couple of occasions. Fuse replaced by DNO and problem solved, and not repeated

 

[Zehroni]

Cartridge fuses can and do just fail - it’s rare but I’ve come across it on a couple of occasions. Fuse replaced by DNO and problem solved, and not repeated

I think this one is as you described "just fail" and i do hope it does not happened again. it was very scary last night to immerse in darkness without knowing what is going on, particularly if whole neighbourhood are lit. However the DNO were excellent, they came out straight a way.

 

[Zehroni]

Another failure would be if there was a short circuit fault in the installation, and you have old rewireable fuses which are much slower to react than a cartridge fuse

the house has been recently extended and all wiring including the main house are brand new. furthermore, all the circuits are connected to RCBO. Hence, I believe they would trip before the main 60A fuse. And that what confused me last night. non of the breakers in my CU was down, yet there is no electricity anywhere in the house.

 

[ericmark]

I cross fingers and hope it does not happen to me. My home could draw over 60 amp, but never see the load get that high, and it is not common for DNO fuses to rupture. Clearly if multi circuits are loaded to max, then total could exceed 60 amp, however 40 amp is my biggest RCBO and to have 20 amp draw from all other circuits does seem unlikely, only way I could really exceed the 60 amps is for two showers to be used at the same time.

So it does seem likely a faulty or stressed fuse in your case, as what you list gets no where near 60 amp. I can see my use and the max I have seen is when showers are used, but in the main the max is just before we go to bed, when making coffee, and the battery is charging. I will admit easy to forget about battery, it is charged 0:30 to 7:30 and since automatic easy to forget it happens. So 5172 watts is kettle 3000 watt, and battery 2000 watt plus lights etc.

Unless you have missed some thing like a battery being recharged, is seems unlikely due to overload.

 

[Zehroni]

Unless you have missed some thing like a battery being recharged, is seems unlikely due to overload.

thanks for your contribution eric no northing just the once I mentioned.

 

[jurassic sparkk]

Was there any recent electrical work carried out?
Are you on a looped supply?

 

[Zehroni]

Was there any recent electrical work carried out?

yes the whole house was rewired 3 years ago when the extension was built. all the circuits are on RCBO.

Are you on a looped supply?

what does this mean?

 

[Ragnar_AT]

A 60 amp fuse should be able to carry something like 90 amps for up to an hour (fusing current) and over 70 amps for an indefinite amount of time (non-fusing current), so an overload seems extremely unlikely.

The only possibility I could see (apart from old age) would be a short between the cutout and the CU, e.g. rodent damage or a rodent getting fried inside the CU but that wouldn‘t likely clear itself.

 

[ericmark]

It was common at one time to bring the supply from the street into one home, and then to another home. Common in ex council houses, however I can see no way this would cause a fuse to blow unless both homes fed from same fuse. I suppose that could be done, but seems very unlikely.

The looped supply has been causing problems with EV charging points, as the demand on the one cable is so high, but really can't see how this would effect what you have had.

 

[securespark]

I have told this story a couple of times on here, but it's a good one.

In the days of Norweb (in the NW), I obtained permission from them to cut the seals in the case of a rewire or board change. I would leave a cert and they would attend a few days after and reseal.

One day I was working on an estate in Chorlton doing a board change.
This estate apparently was the first in Manchester to be built with a leccy supply.

I had cut the seals and removed the fuse and busied myself disconnecting, fitting a new back board etc...

After a while, there was a knock on the door. It was a Norweb guy.

"Have you got electric?"

"No, I've pulled the fuse because I'm doing a board change."

"Bloody hell" said the bloke, "That explains it!"

"Explains what?" I asked.

"This whole side of the street is off downstream of this house!"

"Wait....." I started, trying to figure out what he'd said, "But me pulling an intake fuse for this house shouldn't affect anyone else."

It turned out that the PILC cable was looped from one house to the next, all the way down our side of the street.

But not only that, it was looped on the wrong side of the fuse, so pulling a fuse in any house would turn off the leccy in all the houses downstream of it.

I'm not sure the Norweb guy realised quite how wrong it was, but I made a phone call to their offices to report the situation.

As far as I know, the situation hasn't changed.

 

[ericmark]

That would clearly explain the problem. I was surprised when I had a smart meter fitted, to find that was all the guy does, and he was not permitted to up-grade fuse size, or do any other work, he drew the fuse to do the work, and noted fuse size, but that was the limit to what he was allowed to do.

So it could well be that a fault like @securespark describes could go on for years without being found. Back in the last century when I did work on domestic the clamp-on ammeter was rare, and we assumed turning off main isolator would mean no current through the fuse, so no chance of ionisation of atmosphere when drawing fuse, however what @securespark describes could very well cause a big bang as the fuse is drawn.

 

[ebee]

Indeed,
years ago in the days of area boards, Manweb, Norweb, YEB etc etc then our board sent an actual inspector out. These tended to be time served electricians with experience and additional training for inspection and connections.
Roll forwards a few years, one turned up to do the job and as he was leaving he commented "They might send the joiner to see I done it properly!"
Surprised I asked him to explain.
"Ho I been an inspector for many years but nowadays they train folk up, the one who usually follows me to oversee my work was a joiner until he went on a short course and now he is trained to check I do my job properly! I wonder when I get a decorator or roadsweeper to check my work?". He chuckled at the daftness of the system.