Systematic procedure for tracing repeated fuse blowing in domestic 5 amp lighting.

[JimboMarimbo]

Edwardian terrace with central hanging wire and bayonet sockets for light bulbs with one wall mounted rocker switch per room. Last week the only light that was ‘on’ in ground floor lounge went ‘click’ and the fuse had blown. After just replacing the cartridge fuse and with all light switches in ‘off’ position, I switched the circuit back ‘on’ at the fuse-box, and ‘click’ the fuse blew after maybe 3 seconds.

Trying to remain calm, I removed every light bulb (all LEDs) on the ground floor (upstairs has its own separate ring main installation) and once more replaced the fuse, which once more went ping after a couple of seconds.

From the knowledge of the professionals on this site who will have encountered such a problem before, what would be the most likely reason that they have found: I’m thinking fifty-odd years of light bulbs dangling from the ceiling might have twisted the wiring in the ceiling rose? Or maybe the wall switches for no apparent reason might become fragile inside? These are only guesses, and any word of help that nudges me in the right direction would be appreciated: where to start?

 

[Murdochcat]

I think you need a spark

5A cartridge fuses too

How old is the property / wiring ?

 

[ericmark]

I would think some rubber insulated wire is no longer insulated, could be a rodent of course with PVC, but no magic way to find the fault, it is a laborious task with a meter.

 

[Jurassicspark]

quite hard for a diyer to diagnose the issue if its a problem with the wiring. Any recent work carried out? Banging nails in the wall etc.

question. What type of light fitting is installed in the bathroom? Is it a IP one?

 

[sparkwright]

Could be anything. Outside light full of water? I know it hasn't rained lately.
Single insulated twisted flexes on pendant drops can get brittle at the lampholder, where 100 and 150 W bulbs have been used in the past. Though the light switch would have to be on to blow a fuse.
Rodent damage is the favourite.
Rubber cable more like 65 years+.
Cable trapped by a floorboard or nail quite common.

Photos would help, so we can see what cable has been used - if it is rubber, then it really needs changing completely.

 

[Scally-Ho]

IMO as the fault was also present with all ceiling pendants switched off, the fault is either within a rose or backwards and beyond. It could even be a problem within the CU. As an extra thought, is there a bell transformer fed by the lighting circuit?

 

[endecotp]

what would be the most likely reason that they have found

Customer’s claim that they had removed all bulbs before turning circuit back on turns out to be wrong, they had forgotten to remove the one bulb that had actually blown in the first place.

 

[JimboMarimbo]

Thanks, that's a lot, guys. A property this old with no inter-floor access to the ceiling roses, short of ripping up the first floor floor boards room by room, I will read through your individual posts and ruminate thereon.
As for "I think you need a spark" - if you mean 'sparks' rather than a 'of inspiration', I can hear "you'll be looking at a complete re-wire" from here, right now!

 

[SUNRAY]

Thanks, that's a lot, guys. A property this old with no inter-floor access to the ceiling roses, short of ripping up the first floor floor boards room by room, I will read through your individual posts and ruminate thereon.
As for "I think you need a spark" - if you mean 'sparks' rather than a 'of inspiration', I can hear "you'll be looking at a complete re-wire" from here, right now!

We don't jump on the 'Rewire' band wagon on here, with sufficient information we try to assess the situation then advise.

Are you able to take and post any pictures of wiring, such as unscrewing a ceiling rose cover.

 

[JimboMarimbo]

Thanks, noted.
I find that my stepladder is not going to get me to within safe distance for unscrewing the central rose, the Edwardian ceilings being 3M high.
I would assume that the problem will be on the ceiling rather than on the wall switches, and I thank you for (kinda) confirming this as the likely culprit (s).
I'm inclined to think I should phone a friend with a head for hights to unscrew and photo the roses one by one.
Once done I will post back.
Thanks again.

 

[Scally-Ho]

Another question .. are the ceiling roses plastic or older porcelain type?

 

[Harry Bloomfield]

I would assume that the problem will be on the ceiling rather than on the wall switches, and I thank you for (kinda) confirming this as the likely culprit (s).

You cannot assume that any particular part of the installation is at fault, the fault could be at a switch, a ceiling rose, or almost any part of the lighting wiring, although less likely a ceiling to lamp holder flex, if you are certain all switches are in the off position..

The old way they were wired, was from the fuse board, L+N to joint boxes, one associated with each switch light position, then L+N on to the next joint box, all hidden under the floor.

The more modern way, was to run L+N from the fuse board, to the ceiling rose, or the switch, then loop from that one along to all of the others on the circuit.

The way to determine where the fault is, is to split the circuit in two, somewhere near the midpoint of the loop of L+N, then test whether the fault is before, or after that point. You then split again at the midpoint, and test again. Divide and conquer, until you are down to the actual fault.

As above - provide some close-up photos, and you will get better help.

 

[AndyPRK]

2 tips from me.

If it’s a wylex fusebox, get a plug in 5A MCB. Save a lot of messing with fuses as a
Diyer. But it’s fround upon method.

Split the circuit in half (disconnect the circuit at a ceiling rose)
Repower circuit. That will tell you which half the fault is at.
Then keep splitting down.

It could also get half your lights working again.


Pics will really help us get an idea. Including fusebox.

 

[Harry Bloomfield]

If it’s a wylex fusebox, get a plug in 5A MCB. Save a lot of messing with fuses as a
Diyer. But it’s fround upon method.

I absolutely do not suggest the OP should do the above, but in addition to the above - a lamp-holder, 100w lamp, in series with the 5amp MCB, will avoid the MCB constantly being tripped. Lamp lit, equals fault still in evidence.

 

[Murdochcat]

Thanks, that's a lot, guys. A property this old with no inter-floor access to the ceiling roses, short of ripping up the first floor floor boards room by room, I will read through your individual posts and ruminate thereon.
As for "I think you need a spark" - if you mean 'sparks' rather than a 'of inspiration', I can hear "you'll be looking at a complete re-wire" from here, right now!

Absolutely disagree about the rewire comment. Problem is faults can appear monthly or even many years after the initial installation - it’s just one of those things

Have you removed ALL the bulbs AND even the ones that don’t work as some cheap and nasty imported led bulbs can fail AND then create a dead short