Scottish Power Main "the Bullet" Fuse Blown But Nothing Else, What Could Cause This?

Hi, I'm a landlord and currently have an issue where a main electric board fuse before the meter has blown but not a single fuse or rcd tripped or blew on my fuse board. What could cause such a thing? Surely if it was a faulty appliance in the flat then my fuses would have blown or tripped first? The tenant mentioned flickering lights buzzing and then a loud bang (likely the bullet going) then a little smell of smoke.

I've got an electrician returning to sort tomorrow but it'll take a while and needs the electric board to sign off before tenant can return. I'd appreciate any ideas in the meantime.

Thats more than likely a DNO job, not a sparkies. Sometimes the main fuse can blow simply due to old age.

Andy Guinness

Scottish power came out and replaced the fuse and tested their side but will not turn power back on till fuse box is replaced and tested, hence the need for the sparky.

Do these things really go with age? Is there any other possibilities?

It's mostly old age, how old is the fuse box?

Andy Guinness

My guess is that your fuseboard has BS3036 (rewirable) fuses, and that the fuse for the lights has had the wrong size fuse wire fitted. A fault has occurred on the lighting circuit - hence the bang, you wouldn't hear an HRC fuse blow - which has blown the incomer because it can clear the fault quicker than the (upgraded) rewirable.

Or maybe a fault on the Bus-bar side of the fuseboard or even main switch, before fuses load side.

Hi Riggy, I think you may have been spot on.

A wired smoke alarm, wired into the lighting circuit has completely fried, I mean melted and blackened, looks like a fault within the alarms circuit board. Scottish Power guy thinks that's what blew the bullet fuse. Weird thing is he had to come out twice as first time he didn't correctly restore power and my sparky couldn't do any work without juice to the property! So same guy comes back out and finds low voltage at their end. Turns out loose wire in downstairs flat where my feed comes from! They where having work done the day my fuse blew. I was hoping that might have been the cause but Scottish power guys says not. Says that couldn't blow the fire alarm, and that it had to be the other way round and that my flats dodgy wiring blowing caused vibrations in the cable downstairs working it loose. Can that really be the explanation? My smoke alarms been wired for 3 years without incident, nothing changed in flat electrically apart from that alarm in six years. Yet the day downstairs gets work done my flat blows up and there's a loose wire downstairs yet it's my circuits that caused it all!!! It's a striking coincidence is it not? I'd appreciate some advice on whether that sounds plausible as currently I'm taking a hit of £1000 due to tenants hotel bill and sparky fees made worse by bank holiday, won't be fixed until Wednesday!

I think they are taking you for a ride.

Had the fuse supplying the smoke alarm been replaced with incorrect wire, had it blown.

I don't think that's the case. Scottish Power guy is just giving his view on the original fault. He's fixed the supplier fault and gets no money from me for that, so should have no incentive to not be honest. Also his reasoning sounds very plausible.

The only thing nagging me is why did it happen on the day the downstairs owner has major work done near the electrical unit. Perhaps just coincidence.

No fuse blew in my box. I don't know if it was correctly rated as the box has been replaced. I have the box and it is old and the type Riggy said.

I have seen pieces of 2.5 copper wire fitted in 5 amp fuses. I would imagine a 60/80/100 amp fuse possibly would go before the copper cable.

Amazingly in this day and age people take one opinion over another without hard facts. I do take from your original explanation that a drastic event took place. This can be down to various factors and has nothing to do with vibration, though I could conclude that this is the expression used by that person to express what he knew nothing about.

The last time I had an event such as this was in a property some 5 years ago. A cable was buried without mechanical protection in concrete, water had flooded the ground floor and effected the cable. The resulting fault immediately blow the primary supply.

For all those in the know!

Why did the DNO primary fuse blow?

Loose connection in the head downstairs, hence why lights flickered. Fuse blew due to loose connection that's my thoughts, or they damaged cable downstairs.

Your landlords insurance, which under your care of duty you should have  will cover you for tenants temporary accommodation. It probably will also pay for the emergency electrician but it definitely wont pay for the upgrade/repair to the installation.

My view is old age of the fuse combined with the smoke detector fault. Without knowing if there was a correct size fuse or a nail in the fusebox no one ever will be able to accurately explain this. The connections at the  intake in the flat below had possibly not been touched for 50 years ( when were the flats built/converted ?) so things do come loose. The only vibration would not have been from this fault but from the work being carried out downstairs.

A  couple of years ago i was sitting round a freinds house having a cuppa, his wife turned the vacuum on  and it blew the main intake fuse. No faults, just the surge of the vacuum motor, maybe the fridge compressor  kicking in and old age.

Another point is as a landlord when is the last time you had the electrical installation inspected and a report issued ?

SLIPSHOD AND SLAPDASH said:

Another point is as a landlord when is the last time you had the electrical installation inspected and a report issued ?

Click to expand...

+1

The first two questions I would be asking before trying to come to any conclusions..

1/ What is the actual rating of this "main" fuse??  40A, 60A, 80A, 100A ????

as a flat it may not actually be a very large suppy fuse? 

2/ What does the last periodic inspection report state about the condition of the installation & the max demand?

We are assuming that the installation as whole was all in good condiiton...

need more info to make any suggestions..

The loose connection downstairs was it in the neutral by any chance?

If so then the loss of neutral on the supply may have resulted in 400 volts being seen on your installation and the resulting smoke alarm alarm fry up shorting and taking out the supply fuse as it reacts quicker then a rewirable.

Thanks mate

sparkytim said:

The loose connection downstairs was it in the neutral by any chance?

If so then the loss of neutral on the supply may have resulted in 400 volts being seen on your installation and the resulting smoke alarm alarm fry up shorting and taking out the supply fuse as it reacts quicker then a rewirable.

Click to expand...

Think about it very hard, how can that happen.  ? 

SLIPSHOD AND SLAPDASH said:

Think about it very hard, how can that happen.  ? 

Click to expand...

Take a 3 phase supply.  Each phase will be 230V wrt neutral.

Now disconnect the neutral. What voltage will each phase "see" now?

That depends on the impedance of the load on each phase.  In this case the load is a whole property.

So if the house in question has virtually nothing turned on, it's load will be a high impedance.  But if next door was doing some cooking, and some washing and ironing, it will have a very low load impedance.

So the (now floating) neutral will tend towards the heavilly loaded phase, and therefore could result in substantially more than 230V seen by the property with a very low load.

I'm not saying that's what happened here, but it could.

That was not directed to you Dave. This is a flat in a converted house, do you really think its 3 phase ?

Also the op said connections to his flat. But we will probably never know exactly

IF the property has several flats then it is likely that a 3 phase supply is present. the work in the basement could have disturbed the supply connections and resulted in a loss of nuetral as the cause of the events suggested.