Can a trip fuse expire?

[Slarti]

Last night at about midnight, there was a clunk and the electricity went off.

When I came down to check, the main circuit breaker was in the off position and the fuse for one of the circuits had popped.

I turned the main one back on and watched things come back to life. pushed in the fuse and saw no change. Watched it for a minute or so and then went back to bed, only for the damn thing to go again as I was lying down.

Back downstairs, main switch on, left the fuse popped, checked the downstairs lights, went back upstairs checked the lights there and they were also working, so went to sleep.

This morning I worked out that the circuit that had popped was the one for the lights in the utility room and garages, so I've been out and looked at the wiring in the garages and the lamps and all looks to be OK. The only bit I can't do a visual inspection of is the wiring above the ceiling of the utility room as this is below a flat roof.

I know that I'm going to have to get a man with a meter to check things for me, but I'm wondering could the fuse have gone through age?

It looks like the white one in this image http://www.justclickelectrical.co.uk/blog/when-do-i-know-to-update-my-fuse-box-in-my-house/ and is at least 30 years old as it was here when we moved in.

Regards
Slarti

[dspp]

Fuses can fail for a variety of reasons other than excess current. If you replace it and it goes again then you should be suspicious of a circuit fault.
regards, dspp

[csearle]

...I'm wondering could the fuse have gone through age?.

Hi Slarti,

Nothing is impossible but I think it is relatively unlikely. Much more likely is that something on the circuit has developed a fault and your circuit breaker is doing its job.

You say that the main switch also tripped. Is it an RCD main switch (characterised by having a "Test" button)?

Regards,
Chris
PS Do all the the lights/equipment in the utility room and garage still work (while the breaker is in and before it pops out)?

[Slarti]

...I'm wondering could the fuse have gone through age?.

Hi Slarti,

Nothing is impossible but I think it is relatively unlikely. Much more likely is that something on the circuit has developed a fault and your circuit breaker is doing its job.

You say that the main switch also tripped. Is it an RCD main switch (characterised by having a "Test" button)?

Regards,
Chris
PS Do all the the lights/equipment in the utility room and garage still work (while the breaker is in and before it pops out)?

Yes the main switch is an RCD.

I'll do an experiment on the utility room lights and see what happens.
Not sure I'd get to the garage, so I'll have to send Mrs S out into the cold to watch

I'll report back
Slarti

[Slarti]

OK, that's a bit odd.

I turned all 5 light switches on, we opened the garage doors and Mrs S stood so that she could see into both and when I reset the fuse everything came back on, except the outside light.

So I turned each of the working lights off and the fuse didn't trip, held my breath and turned off the outside light and now, 5 minutes later nothing has tripped.

So it looks as if the culprit is the outside light, or its wiring. I've got things to do today that will prevent me from getting the ladders out so that I can change the lamp in the outside light and as I'm working away for a couple of days it'll be Thursday before I can have a go at it.

Again, once I have, I'll report back.

Thanks for the assistance
Slarti

[dspp]

Slarti -

I have now looked at your link. http://www.justclickelectrical.co.uk/bl ... -my-house/ I am fairly sure that white 'fuse' you describe is not actually a fuse. The brown things either side of it are real fuses that you put fuse wire in. The white thing is a circuit breaker that ?? Wylex ?? made to fit onto the same fittings in the old-style Wylex fuse boards as they worked towards what we now call consumer units. I am not an electrician (though I am an electrical engineer) and I have had dealings with many of these old Wylex units. Basically if this is your house and you are planning to stay in it a fair while I would be planning to replace the whole fuse board in the not too distant future with a new style consumer unit.

Meanwhile the good/bad news is that miniature circuit breakers (MCBs) which the Wylex white widget almost certainly is are able to fail, but don't often do it. So it is likely, but not guaranteed, that you have a real circuit fault. However there is a slim chance it is a MCB failure. The real bad news is that getting hold of a replacement for one of these old Wylex plug-in widgets is tricky these days. There is no way around this except getting an electrician out, and in the meantime leave that circuit de-energised if you cannot locate the fault yourself (it may be a light blowing etc*). Ask for an older electrician if you have a choice as the youngsters may not all have seen some of these items and so will be faster to condemn them prematurely.

regards, dspp

* it looks like our posts have crossed over.

[csearle]

Again, once I have, I'll report back.

Look forward to hearing your report.

The RCD usually only trips if there is a fault to Earth or a fast voltage spike. Your MCB usually only trips if there is either a moderate overcurrent for a longer period of time or a large overcurrent* for a shorter period of time.

When RCDs trip (after long periods of not tripping) it is often the case that liquid is involved. For lighting circuits that usually means a leaky outside light. (For other circuits it usually means a kettle/oil-filled heater/immersion heater/fridge/freezer/washing machine.)

You say that you

Watched it for a minute or so and then went back to bed, only for the damn thing to go again as I was lying down.

Which suggests to me that the RCD went the second time (otherwise I guess you wouldn't have noticed had it only been the MCB) so, given that the outside light is no longer working, I reckon it is/was water getting into said outside light. These faults can clear if the water drains or evaporates away.

We'll see.

Regards,
Chris
* Unlikely in your case as you wouldn't have been able to reset the MCB at all.

[jfgw]

The real bad news is that getting hold of a replacement for one of these old Wylex plug-in widgets is tricky these days.

Screwfix do them:

http://www.screwfix.com/p/wylex-6a-sp-t ... -mcb/48030

They simply plug in. If you are replacing a fuse with one of these mcbs, you have to replace the registration plate as well but these come with the mcbs and are held in with a single screw. If you are replacing an mcb with a new one, you simply have to pull out the old one and plug in the new one.

If the installation is this old, is the rcd a 100mA one or a 30mA one?

Julian F. G. W.

[Slarti]

Again, once I have, I'll report back.

Look forward to hearing your report.

The RCD usually only trips if there is a fault to Earth or a fast voltage spike. Your MCB usually only trips if there is either a moderate overcurrent for a longer period of time or a large overcurrent* for a shorter period of time.

When RCDs trip (after long periods of not tripping) it is often the case that liquid is involved. For lighting circuits that usually means a leaky outside light. (For other circuits it usually means a kettle/oil-filled heater/immersion heater/fridge/freezer/washing machine.)

You say that you

Watched it for a minute or so and then went back to bed, only for the damn thing to go again as I was lying down.

Which suggests to me that the RCD went the second time (otherwise I guess you wouldn't have noticed had it only been the MCB) so, given that the outside light is no longer working, I reckon it is/was water getting into said outside light. These faults can clear if the water drains or evaporates away.

We'll see.

Regards,
Chris
* Unlikely in your case as you wouldn't have been able to reset the MCB at all.

Well after various delays and interruptions I've finally managed to get up the ladder and do the deed.

The cover of the lamp seemed to be well seated to the frame as I had to use a screwdriver to prize it free, but when I got hold of the lamp, it was damp, not just cold so water must be getting in somewhere.

Inserted new lamp, turned it on and ping, both MCB and RCD had gone again.

I think I should get somebody to check the wiring, to be on the safe side.
And I may replace the unit as it is not exactly new and the seal between cover and base looks as if it may have gone.

What fun
Slarti

[csearle]

I think I should get somebody to check the wiring, to be on the safe side.
And I may replace the unit as it is not exactly new and the seal between cover and base looks as if it may have gone.

The water might well explain the RCD tripping but not the MCB. If you are planning to replace the fitting anyway then you could (after switching it off) dismantle and remove it, make sure the cores of the cable are all safely separated from each other, and turn it back on to see if the RCD/MCB still trips. This will help establish whether the fault is in the wiring or the fitting.

Regards,
Chris

[Slarti]

To finish this one off, I got an electrician around on Thursday and he discovered that the wires inside the fitting had been close to the lamp ans so, due to the heat 100W incandescent gives off, the coating had turned to to dust and the copper wire had degraded. This allowed contact with something, causing the trip out. (sorry about the technical terms)

He replaced the wire for about 2', to make the work easier and it is now working fine.

I have an LED lamp on order to replace the incandescent.

Thanks for all the help
Slarti

[csearle]

To finish this one off...

Thanks for the explanation Slarti, always good to hear the ending - especially a happy one.

Chris