63A Switch Fuse Melted

2011

A work colleague noticed a burning smell from his consumer unit. This was the culprit:



I have seen three of this type of switch fuse fail in a similar fashion.
IMHO the design of the type shown below (this example is a Hager unit) is a far superior.
It is safer / more robust design as there are less connections and it is less likely that the fuse will be loose.



As far as I recall a number of this type (as shown in the first picture) were recalled. Anyone else remember this?

Just An Opinion

Yea I'm surprised these screw ins are still used in units today, far too common them coming loose.

LeBash

Just An Opinion wrote: »

Yea I'm surprised these screw ins are still used in units today, far too common them coming loose.

Probably because the drop in style caught fire a few years ago.

meercat

have come across this too ,a few times
luckily there was nothing flammable close to it

M cebee

fairly regular callout issue i'd say
i've certainly seen loads of them


funnily enough i don't recall too many issues with the 'recalled' drop-in types over the years:)


i think some cases are overload related related-dunno how many?

2011

M cebee wrote: »

i think some cases are overload related related-dunno how many?

An overload should not be possible.
If this unit was fit for purpose (and properly installed) the fuse should operate before the unit can experience an overload condition.

funnily enough i don't recall too many issues with the 'recalled' drop-in types over the years

I was referring to the type of switch fuse unit shown in the first picture as being recalled.

meercat

2011 wrote: »

I was referring to the type of switch fuse unit shown in the first picture as being recalled.

have to say i didnt know there was a recall on that type of fuse unit

Something like this happened in my parents' house many years ago, probably 1995 or so. Their 50A fuse blew after they went overboard with heavy appliances one night. It was one of the screw cap types. My dad replaced it with a 63A fuse from his toolbox but then the following morning we got a very strong smell of burning plastic from the consumer unit, turned out it was because of the fuse.

2011

meercat wrote: »

have to say i didnt know there was a recall on that type of fuse unit

...as far as I remember. It was just a particular make of the type shown.

meercat

2011 wrote: »

...as far as I remember. It was just a particular make of the type shown.

i thought it was a slide in type with a cover that flipped up but didnt engage properly causing arching

M cebee

2011 wrote: »

An overload should not be possible.
If this unit was fit for purpose (and properly installed) the fuse should operate before the unit can experience an overload condition.


I was referring to the type of switch fuse unit shown in the first picture as being recalled.

they do seem to burn out, rather than blow in some cases where the installation load is excessive


this wouldn't be the case in more expensive units with hrc blade fuses

M cebee

EEC D02 63A AC 22B
Gould 5861.063 DO63A AC22
Lindner 5861.063 DO 63A AC22
NES UE 440V 63A
REGIS OSLF 63 1P
Hi 240V/415V-63A
Hi DO2 63A 5.5W ac 22B


i was looking for info on that-i think those are the affected ones

jeez that was a major hype for registered contractors a good few years back

don't think i was called back to any that actually caused trouble

2011

M cebee wrote: »

they do seem to burn out, rather than blow in some cases where the installation load is excessive

Only if the unit is faulty or not fitted correctly.

The design intent is that a fuse should blow before the current exceeds the rating of the fuse holder.

2011

M cebee wrote: »

EEC D02 63A AC 22B
Gould 5861.063 DO63A AC22
Lindner 5861.063 DO 63A AC22
NES UE 440V 63A
REGIS OSLF 63 1P
Hi 240V/415V-63A
Hi DO2 63A 5.5W ac 22B


i was looking for info on that-i think those are the affected ones

jeez that was a major hype for registered contractors a good few years back

don't think i was called back to any that actually caused trouble

Yes, you are correct.
Here is a link to it.

M cebee

2011 wrote: »

Only if the unit is faulty or not fitted correctly.

The design intent is that a fuse should blow before the current exceeds the rating of the fuse holder.

not so sure about that ime

2011

M cebee wrote: »

not so sure about that ime

There is little point in having an over current protective device that is prone to melting if it experiences an over current.

Why do you think there was recall by Director of Consumer Affairs?

Bruthal

2011 wrote: »

Why do you think there was recall by Director of Consumer Affairs?

Main switch fuses that are badly designed or have a problem, can likely burn out when well below the fuse rated current.

It does not mean they are burning out only at the overloading stage, as if to indicate that this proves ones not involved in recalls, wont burn out when loaded at 60 or 70 amps.

hufpc8w3adnk65

I've replaced 3 of those types in 15/16 years and 2 of the hager type in the second pic.The hager ones are sturdier I think!more common you'd have too replace them as a result of a loose connection

Bruthal

2011 wrote: »

An overload should not be possible.
If this unit was fit for purpose (and properly installed) the fuse should operate before the unit can experience an overload condition.

Yea if the switch fuse is fit for purpose, it shouldnt be possible to overheat due to overload, as long as the fuse is properly fitted.

Bruthal

Mohammed Scruffy Animal wrote: »

I've replaced 3 of those types in 15/16 years and 2 of the hager type in the second pic.The hager ones are sturdier I think!more common you'd have too replace them as a result of a loose connection

Probably loose fuses is another main factor. Recalls are probably down to the fuse contact mechanism not working reliably.

Once overheating starts, oxidation begins, likely making the problem worse, accelerating the failure process.

M cebee

the different types of neozed fuse unit should work reliably under overload conditions

i'm not convinced they always do

Bruthal

M cebee wrote: »

the different types of neozed fuse unit should work reliably under overload conditions

i'm not convinced they always do

No id be doubtful myself if all switch fuse units continuously loaded at 70 amps for example, would reliable work for its expected lifespan, or very long at all.

If it was loaded at 80 to 90 amps, the fuse would probably operate reasonable quickly. But at just over the fuse rating regularly, and sustained, a fair bit of heating would seem likely.

If it is designed for 63 amp fuses and is supposed to be fit for that purpose, the housing should be rated for 100 amps or something of that sort possibly, as they could be overloaded well into the 80+ amps for sustained periods without the fuse going.

2011

Bruthal wrote: »

If it is designed for 63 amp fuses and is supposed to be fit for that purpose, the housing should be rated for 100 amps or something of that sort possibly, as they could be overloaded well into the 80+ amps for sustained periods without the fuse going.

Well put.

The manufacture should to look at the fusing characteristics and design the switch fuse accordingly.

If it could guaranteed that the unit would never experience an over current condition then it would be possible to argue that a switch fuse is not required in the first place.

Bruthal

2011 wrote: »

If it could guaranteed that the unit would never experience an over current condition then it would be possible to argue that a switch fuse is not required in the first place.

The fuse/holder would be more to protect the busbars and link wires more so than itself really. But with 63 amp MCBs protecting the tails to the MCB board, the board itself would only seem to need a switch alright.

If a new meter is staying beside the MCB board in an installation in a rewire these days, is the MCB required then? I thought it might only be a requirement when the meter goes out into an outside box, rules wise anyway.

M cebee

Bruthal wrote: »

The fuse/holder would be more to protect the busbars and link wires more so than itself really. But with 63 amp MCBs protecting the tails to the MCB board, the board itself would only seem to need a switch alright.

If a new meter is staying beside the MCB board in an installation in a rewire these days, is the MCB required then? I thought it might only be a requirement when the meter goes out into an outside box, rules wise anyway.

-no i don't think you need to protect tails if main DB and meter are side by side



if the main ocpd(10ka 63amp mcb) is fitted in the cabinet then i think a 'main isolating switch' should suffice in the main DB

can't see the benefit of 2 63amp ocpd's in series unless i'm missing something obvious

2011

Bruthal wrote: »

The fuse/holder would be more to protect the busbars and link wires more so than itself really. But with 63 amp MCBs protecting the tails to the MCB board, the board itself would only seem to need a switch alright.

Yes.

If a new meter is staying beside the MCB board in an installation in a rewire these days, is the MCB required then?

Not sure. I am not a fan of these MCBs TBH.

Bruthal

M cebee wrote: »

-no i don't think you need to protect tails if main DB and meter are side by side



if the main ocpd(10ka 63amp mcb) is fitted in the cabinet then i think a 'main isolating switch' should suffice in the main DB

can't see the benefit of 2 63amp ocpd's in series unless i'm missing something obvious

The only benefit I see was you can completely disconnect the MCB board, and also possibly avoid operating the ESB cutout if there was a short.

I was thinking it is a rule requirement only if out in an outside box alright, more than a couple of meters away.

2011

Bruthal wrote: »

The main benefit I seen was you can completely disconnect the MCB board, and possibly avoid operating the ESB cutout if there was a short.

Is there not an isolation switch on the ESB meters though?

Bruthal

2011 wrote: »

Not sure. I am not a fan of these MCBs TBH.

No, nor am I to be honest.

Bruthal

2011 wrote: »

Is there not an isolation switch on the ESB meters though?

Yes, so there is even less benefit to having them. Pointless really, apart from maybe avoiding blowing the main cutout fuse in a short.

Not really worth the hassle.

2011

Bruthal wrote: »

Yes, so there is even less benefit to having them. Pointless really, apart from maybe avoiding blowing the main cutout fuse in a short.

Even at that there is every chance that the cut out fuse would blow first if there was a short.

Not really worth the hassle.

Sometimes there just seems to be a policy to make up rules for the sake of being seen to do something.

M cebee

i'm not sure that it's a good idea to remove the switchfuse/mcb from the distribution board and replace with switch


it might be safer to leave the 2 in series in case there's a prob and you have tampered with pre-assembled DB


although i've done it as it goes against my logic to have 2 63amps in series

Bruthal

2011 wrote: »

Even at that there is every chance that the cut out fuse would blow first if there was a short.

Sometimes there just seems to be a policy to make up rules for the sake of being seen to do something.

Yes indeed

Bruthal

M cebee wrote: »

i'm not sure that it's a good idea to remove the switchfuse/mcb from the distribution board and replace with switch

No I wouldnt think that was being suggested, just that it is sort of redundant with the MCB in the line.

M cebee

Bruthal wrote: »

No I wouldnt think that was being suggested, just that it is sort of redundant with the MCB in the line.

yah i was talking to myself really

Bruthal

M cebee wrote: »

yah i was talking to myself really

A sure sign of madness, as seen in my location on the left.

Andrew_Doran

Bruthal wrote: »

I was thinking it is a rule requirement only if out in an outside box alright, more than a couple of meters away.

I was reading about this last week.

The regs say it's required if the tails are longer than 3 metres. Seperate to that the ESB code of practice talks about an IP rated enclosure and mounting it in their cabinet, but nothing about when the meter and distribution board are both inside.

I think I also read about an amendment to the rules that says a type C MCB is now permissible as main OCPD because of nuisance tripping. I wonder what the motivation was for moving to MCBs.

M cebee

how tight does the fuse holder and cable connections actually need to be to prevent overheating later?

Bruthal

M cebee wrote: »

how tight does the fuse holder and cable connections actually need to be to prevent overheating later?

Id say there is a good variation, as to how tight a connection is, has a bearing, which will depend on the overall contact area between wire end, and terminal.

Imo, lugs are the best way of creating a connection which will reliably handle the capacity of a cable or wire, and much more so as they get bigger, since they convert the end of the cable into a nice flat contact area.

But its probably the fuse contact which causes most of the problems in them sw fuses. They have a nice flat contact area also, but unlike lugs, are depending on just being held in place by the holder setup rather than tightly clamped.