Fuse size, how often does one check it?

[ericmark]

The re-wire I had done was cheap, I knew this and it suited me, the garage was powered from a switched FCU in the bedroom with an overhead cable, in the garage there was just one double socket, and a switched FCU as a light switch with two simple bulbs. I was good enough when fitted, but then realised I really needed a double socket either end of garage and also two way switching of the lights, from main door and side door.

Because the light switch was a FCU to turn into two way I replaced it with a grid fuse holder and two way switch, after changing I then went to swap the fuses, I had expected to find a 3A for the lights, as there would be little point in a fuse same size as the one in bedroom.

However found fitted with 13A, not really a problem, and likely it breaks no rules, however I now wonder what else? Had I not swapped it to two way switching I would have not opened the fuse holder, simply no need to look. It is 9.5 years before it needs an EICR and although one may look at a MCB size, how often does one actually draw a fuse to see what size it is.

 

[EFLImpudence]

Likely a light doesn't really need a fuse at all, it's just what we do.
Without looking (or someone doing something stupid) it could be no more than 13A.

Can the light cause an overload sufficient to melt the cable?
Is the cable capable of handling the fault current of the upstream OPD?



I do like the way you maintain everyone has an EICR every ten years.

 

[ericmark]

As I say not really a problem, the 13A fuse in the bedroom would protect cable even if a bolt was used in the garage, in fact if they had used a simple light switch, it would have been easier to convert to two way. But I realised I have never bothered checking fuse sizes at home. I would never fit wrong size, so what is the point checking? Only with some one else's house would I look.

 

[JohnW2]

As EFLI has implied, when one is talking about fixed wiring, hence a minimum of 1mm² cable, and provided that the cable is not buried in thermal insulation then, if you are one of those people who feels/believes that the fuse "is only there to protect the cable", you might as well always use 13A fuses in FCUs.

I wouldn't do that (and I don't think you would, either), but I am not "one of those people"!

Kind Regards, John

 

[sparkwright]

It seems to me once you start looking closely at someone else's work you do find some surprising issues.

I had a look at a budget partial re-wire job someone had done. Looked reasonable at first glance. I loosened off one light switch (to replace some rather ill-fitting 3.5mm screws) to find one earth wire not in the earth terminal with the other one.

Then I removed another light switch (as I needed to fix a BT cable round the architrave and this was where the next cable clip needed to go) and there was a broken live wire.

Another job I found a 16 amp MCB serving a lighting circuit.

Another job I found joists hacked into to accomodate poorly positioned down lights.

I am forever finding 13amp fuses fitted where perhaps 3 or 5amp ones would be more suitable - though we don't want a long debate about that.

Nothing new here of course, but goes to show what still goes on with professional electricians nowadays.

 

[DaveHerns]

How many people would find a 13amp fuse in the FCU for their boiler if they looked?

 

[sparkwright]

How many people would find a 13amp fuse in the FCU for their boiler if they looked?

TBH, not many. Boilers do seem to be the appliance people are careful to fit a 3amp fuse.

People do worry about the circuit boards in boilers getting wrecked as expensive to replace, yet a recent discussion here suggested there would be internal fuses for this.

 

[Risteard]

Another job I found a 16 amp MCB serving a lighting circuit.

Something which is expressly permitted by BS7671 presuming that everything is designed appropriately.

 

[sparkwright]

Something which is expressly permitted by BS7671 presuming that everything is designed appropriately.

Yes, agreed, but I think the one I had seen was more likely to have been an error, probably mis-read the 16 for a 6, because I think it's fair to say in the real world people nearly always choose a 6amp protective device for lighting over a 16amp one.

 

[JohnW2]

People do worry about the circuit boards in boilers getting wrecked as expensive to replace, yet a recent discussion here suggested there would be internal fuses for this.

I rather doubt that, if it had to operate, any fuse, on the PCB or external, would often protect micro-electronics from irreparable damage.

Kind Regards, John

 

[sparkwright]

It was drummed into me years ago that boilers should have 3amp fuses, so I always make sure of this and it gives me peace of mind.

 

[JohnW2]

It was drummed into me years ago that boilers should have 3amp fuses, so I always make sure of this and it gives me peace of mind.

Fair enough. Similarly, as you probably recall, it was drummed into me years ago that fuses did not exist only to protect cables, and that I should always use the smallest fuse appropriate for the load. That's why I must be one of the most prolific users of 1A BS1362 fuses I once found some 0.5A ones, but haven't seen them for many years!

Kind Regards, John

 

[sparkwright]

Fair enough. Similarly, as you probably recall, it was drummed into me years ago that fuses did not exist only to protect cables, and that I should always use the smallest fuse appropriate for the load. That's why I must be one of the most prolific users of 1A BS1362 fuses I once found some 0.5A ones, but haven't seen them for many years!

Kind Regards, John

Yes, I was also taught that fuses did not exist only to protect cables, and to use the smallest fuse possible to match the load.

When I would buy a pack of fuses from Woolworths, the card would indicate which size fuse for each typical appliance, and suggested wattages for these appliances would also sometimes be listed.

I seem to remember a black and white television was recommended to have a 3 amp fuse, and a colour television to have a 5 amp fuse.

 

[winston1]

It was drummed into me years ago that boilers should have 3amp fuses, so I always make sure of this and it gives me peace of mind.

But is has been pointed out many times that those same boilers are used on the continent straight off 16amp circuits with no problems.

 

[sparkwright]

But is has been pointed out many times that those same boilers are used on the continent straight off 16amp circuits with no problems.

Ok.