Blown 30 amp fuse - age?

[jssm18362]

Hi all

I'm not an electrician by any means but retired from mechanical engineering. I have inherited a semi-detached bungalow which has mostly old wiring from when it was built - mid 60's I think. About 2 am the 30 amp fuse blew for room sockets. Nothing has been changed recently and since the fridge was connected I just replaced the fuse and all is well. Could it simply be an age issue? Nothing should be happening at that hour.

Would £2000 be around the minimum I would be paying for a rewire? Not sure about the lagality of the current wiring - the most recent work was to install some storage heaters about a decade ago and these have modern fittings.

Thanks for any help.

Steve

 

[PrenticeBoyofDerry]

It could well be that the fuse has got tired and it's time has come.
If the new fuse has not blown, it is likely there is not a fault condition.
Most of your existing cable are of an age that it would be worth considering a rewire. As to it's safety you would be best having a period inspection done on it this will give you a good idea what condition the installation is in, how safe it is and how long it would be considered to continue to be safe.
The cost of a rewire would depend on the size of the house and what you want installing?

 

[Space cat]

Earlier this year, I had a load of trouble with random breaker tripping on our downstairs ring. The first one must have happened during the night when only the fridge and freezer were on so I moved these to a double extension lead plugged into a different circuit. The breaker reset without a hitch and everything was fine.

At this point I was considering the possibility of an intermittent fault in either the fridge or the freezer so it came as a bit of a relief when the thing tripped again a day later. And so I started the tedious process of checking around the ring looking for anything that might trip a 32 amp breaker but allow it to be reset immediately.

The fault turned out to be a bad wire coming through a wall to an outside socket. The (red) insulation on the live core was mostly black where it emerged from the outer sheath and the earth wire came away with the socket! My best guess would be that a leakage path from live to earth was slowly carbonizing until it finally burnt through and tripped the breaker - but in doing so it was blowing away enough metal to break the connection.

Since your wiring is old you might have a similar problem. If you have any outside sockets they would be the first place to look (power off of course) but the fault could be anywhere: any socket, any junction box or even a length of cable nibbled by mice. You'll have to check everything on the circuit, not forgetting FCUs that might be out of sight. Good luck, you'll need it.

 

[ban-all-sheds]

Did you really need to use 21 smilies in that post, 3 at a time?

 

[jssm18362]

Thanks for the prompt replies.


It certainly woke me up! I have had issues with a switched off light (new type) flickering too.

The semi is a two bedroom bog standard. I could perhaps do the rewiring myself but the regs don't attract me or the work involved!

Steve

ps The fridge is fairly new. Only new thing added recently is a mini-hifi and that was on standby.

 

[JohnD]

if you can trace a damaged cable or accessory, regulations allow you to replace the damaged item without having to notify.

consider the possibility of rodent damage, especially underfloor or in the loft.

btw if it is 1960's and a rewirable fuse, it is most unlikey to blow spontaneously and when lightly loaded.

hello mr grumpy

 

[Space cat]

I have had issues with a switched off light (new type) flickering too.

If, by "new type", you mean a compact fluorescent (aka low energy) lamp, this is a separate issue unrelated to your fuse problem. It's not unusual for these lamps to flicker when they're used with two-way switching. This isn't a 'fault' as such but a design flaw - but rather than go through it all I'll just point you here:

//www.diynot.com/forums/electrics/light-flashes-when-off.293478/#2136677

But there is another, more ominous, possibility. The earth wire in the switch cable might not be connected. It might not even exist! Without an intervening earth, the capacitive coupling between the live and switched live cores could make a CFL flash.

 

[bernardgreen]

Even with the earth wire in place the capacitive coupled trickle of energy from live to switched live is often enough to flash CFLs or make LEDs glow dimly.

The solution is

Capacitor 0.047uF micro Farads 250 volts AC in series with a resistor 100 ohm connected between switched live and neutral.

Which come pre-packaged as a contact suppressor from RS Components

RS Stock No. 206-7847
Manufacturer Evox-Rifa
Manufacturers Part No. PMR209MB5470M100

Most convenient place to fit is across the affected lamp in the ceiling rose.

There are other sources of the contact suppressors



Read more: //www.diynot.com/forums/electr...fan-in-bathroom.295236/#2151647#ixzz1dzE8XmUW

 

[bernardgreen]

Back to original question

For a 30 amp fuse to blow requires 7 kilowatts of power to be disipated somewhereand for long enough that the fuse has time to melt. This is disioated either in appliances working normally or at the location of a fault. In the case of a fault disipation of that 7 kilowatts of power is a serious fire risk if it is prolonged.

Assuming it was wired with 30 amp fuse wire then the fault is serious.

When a house changes ownership different furniture is put in place.

Badly installed cables that have survived for years trapped between floor board and joist may now be under heavy furniture and become squashed to the point they short out.

 

[jssm18362]

Perhaps it was just age or the rat idea could be the reason. It is probably the season for them to be about under the house. I hope the little blighter learnt his lesson - I'll expect to find some teeth embedded in a cable and a blackened corpse nearby. That assumes I can persuade some kid with candy treat to crawl about under there (joke).

There have been no problems with this circuit that I know of and the sockets are lightly loaded - only a fridge and some TV, Hi-Fi and computer stuff but probably all less than 1 Kw when all on which is rare.

The point raised about weight compressing cabling might be relevant to another problem. There is a fault in the lighting for a few rooms that I have not got around to checking. This occurred over a short period when the fuse blew and I put it down to some work on a cooker hood and wiring for the fan. There is one particular area in the loft where quite some weight is concentrated (over the best supporting walls below) and perhaps this has damaged the cabling. There is no flooring and the cabling is on top of the joists. The fuses are the old ceramic wired type. Everything appears to work normally still after I mended the fuse.

Thanks again for all comments - I think perhaps an inspection is probably wise.

Steve

 

[jssm18362]

I'll look into the flickering light - has not been much of an issue but it might mean the whole wiring does need a proper check.

Cheers, Steve

 

[jssm18362]

Seems a bit odd that everything appears to be working OK after I mended the fuse. I had a thought that perhaps it might have been the immersion heater but that is working fine too. All the appliances should fail at the fused plugs shouldn't they. Perhaps it was shoddy Chinese fuse wire (sorry China - different era) and do they suffer from thermal cycling fatigue?

Cheers, Steve

 

[securespark]

No. Sometimes, you get the CPD tripping before the 1362.

 

[Space cat]

All the appliances should fail at the fused plugs shouldn't they.

Yes, although it's always possible that a massive fault current might take out both fuses. But you can eliminate that cause quite easily. If a faulty appliance did it, you'll now have one that doesn't work.

Perhaps it was shoddy Chinese fuse wire --

No!

if it is 1960's and a rewirable fuse, it is most unlikey to blow spontaneously and when lightly loaded.

If you can't point the finger at an appliance, you have a circuit fault somewhere and you need to find it. It might be a socket, FCU or junction box that's got damp. That's why I asked if you had any outside sockets. Outside lights are sometimes fed from an FCU on a ring but somebody might have cut corners and connected one straight in. Or maybe the FCU kept blowing fuses so they put a piece of brass bar in there.

 

[jssm18362]

There aren't any external sockets that I can locate - there has been external lighting which is not working. Perhaps my dad (previous owner) used some dodgy fusewire - unlikely as he was quite capable with electrical things in general but he was no electrician.

Steve