Consumer unit cartridge fuse size help

[HamsterJam]

Today I helped replace a faulty light switch at a friend’s house.
After swapping the switch, they re-inserted the fuse and the lights flickered on then went out.
On further investigation, the 5A cartridge fuse is too small in diameter and possibly length for the fuse carrier meaning it only makes an intermittent connection. The fuse looks the same diameter as a standard plug fuse which I think is 6mm.
Looking online, I can’t see larger diameter 5amp cartridge fuses. Can anyone shed any light (no pun intended) on this please?
The carrier is colour coded white.
Fully appreciate that in an ideal world the CU should be replaced with a modern unit containing RCBOs but it would be useful to have a fix until funds permit an upgrade.

 

[Sideways]

Borrowed from wikipedia

• BS 1361 for cartridge fuses for a.c. circuits in domestic and similar premises
• BS 1362 for cartridge fuses for BS 1363 power plugs
• BS 1363 for mains power plugs and sockets

So, the answer is BS1361 standard cartridge fuses for a consumer unit. Much fatter than plug top fuses.

Skinny UK plug top fuses are made to BS1363 and the UK 3 pin plug and socket they are used with are standardised according to BS1362

 

[HamsterJam]

Thanks @Spectric, useful but that doesn’t appear to be the solution for the situation I found…
BS 1361 (consumer unit) cartridge fuses vary in diameter according to rating with 5 amp being 5.3mm diameter.
BS1362 (appliance plug) cartridge fuses are all the same diameter irrespective of rating this being 6.3mm.
The fuse installed in my friends consumer unit is likely to be BS 1361 yet appears to be too small allowing it to literally rattle in the clips in the fuse carrier.
I would be very surprised if the fuse carrier in the consumer unit was designed to take 6.3mm BS1362 plug-top fuses and there was no indication of there being any wear or damage to the spring clips the fuse fits into. (I did consider bending the clips inwards to establish a good contact but they were very solid).
Another option might be the carrier is designed to take a higher rated (and hence larger diameter) BS1361 fuse but again, I find it difficult to believe anything other than a 5amp fuse would be used to supply a domestic lighting circuit and the carrier is colour coded white which IIRC is 5amps.
There are two lighting circuits in the installation in question and both were the same.
I’m still scratching my head over this one.

 

[MikeJhn]

What make is the Consumer Unit, not that its recommended, but they may make an MCB or RCBO that fits.

 

[Sideways]

This seems to give a good picture of common bs1361 fuses.
It does indeed include a 5a that's even smaller than a plugtop fuse.

https://www.stevensonplumbing.co.uk...EqHz9CxxtF6LSgddRzKvXQ7huxLhk_HHSZs13c3r1ZzL7

I'll admit, this caught me out as I skipped cartridge fuses at home and went from an ancient wylex rewireable CU to a new board full of RCBOs. I've replaced a few fuses in other people's fuse boxes but I don't think I've ever swapped out a 5A. People don't plug stuff into lighting circuits and changes to LED typically only reduce the load, so a properly installed lighting circuit just keeps working.

Is the fuse carrier Wylex style made in 2 parts ? The plug in carrier itself and the coloured skirt ? The carrier part should be colour coded somehow or marked with the amp rating. The two do match, yes ?

There are plenty of other types including the MEM ones with big coloured dots on the front made in just one piece, so just scratching my head here.

 

[Spectric]

Thanks @Spectric, u

I know both myself and @Sideways start with an S but we are not the same !

As for your problem that board sounds obsolete, does it actually have any circuits protected by a residual current device (RCD) ?

The only place you find cartridge fuses now in domestic is the incoming main fuse or within plugs. In industrial you find other odd looking types such as the bottle fuse.

 

[HamsterJam]

I know both myself and @Sideways start with an S but we are not the same !

As for your problem that board sounds obsolete, does it actually have any circuits protected by a residual current device (RCD) ?

The only place you find cartridge fuses now in domestic is the incoming main fuse or within plugs. In industrial you find other odd looking types such as the bottle fuse.

View attachment 187191

Oops - sorry @Spectric and @Sideways for confusing you - you both appear as an S on a brown background on my phone.
Yes, definitely an obsolete fuse board well overdue a change and there was no evidence of an RCD/RCCB anywhere although there is very little space near it with the meter hiding in an external meter cabinet.
I agree that the CU really needs replacing but our friend has limited means so I can’t see it happening soon.

As regards the make - I should have looked but didn’t. It did however have large coloured dots on the fuse carriers which were one piece if that helps. I don’t think it was MEM though as those are usually clearly branded and I don’t recall there being any specific branding on the carrier.
I’ll try to get make and photo of it next time I’m there.

 

[Sideways]

Maybe MEM

 

[Sideways]

Oops - sorry @Spectric and @Sideways for confusing you - you both appear as an S on a brown background on my phone.

Let's see if that helps

 

[Spectric]

I agree that the CU really needs replacing but our friend has limited means so I can’t see it happening soon.

I would say that having an RCD on the sockets is an absolute minimum when it comes to safety, these devices save lives and if the board is obsolete I really dread to think what the wiring is like so making an RCD even more important.

 

[HamsterJam]

if the board is obsolete I really dread to think what the wiring is like so making an RCD even more important.

To be honest, the t&e behind the switch I replaced was in very good condition. - 1.5mm white pvc outer sheath with red/black conductors. Earth correctly sleeved in green/yellow and the black sporting a red sleeve.
I can’t vouch for any of the other wiring in the house.

 

[Spectric]

with red/black conductors

That means it is old wiring, new colors are Brown and Blue since around 2005.

 

[Sideways]

So's mine.
45 years old and still fine.
The old wylex fuse board was only replaced 2 years ago.
Domestic T&E is designed to last 50 years +

 

[Dabop]

So's mine.
45 years old and still fine.
The old wylex fuse board was only replaced 2 years ago.
Domestic T&E is designed to last 50 years +

One thing to watch out for, 'some' of the old wiring gets insulation breakdown- looks fine on the outside, but if you cut back some of the outer insulation, its green on the copper and 'slimy' inside- and it can cause the insulation breakdown voltage can go lower (the oily stuff is still 'ok' but the green stuff can be conductive and cause tracking if there is any cracking or deterioration of the internal insulation- it can cause apparently good looking wiring to fail (commonly called 'green gunge' or 'greening' lol, is usually found in earlier TPE/T&E from the 1960's/70's with red/black colours inside but can sometimes be found in newer installations as well- in really bad cases you can start getting that 'green goo' oozing from the outlets holes, but its bad long before that happens!!!

By the time it gets like this- its BAD...

VIR or TRS (the black stuff from the 60's and earlier- 'usually' round, but sometimes looks like modern TPE in the 'flattened' form)- also has red and black internal colours is also extremely dangerous and should be replaced even if it 'looks ok'- it can become very brittle and crack if flexed, leaving exposed wires

In either case if found, a full insulation test and inspection should be done at the minimum, and a rewire is highly recommended...