Older style fuses versus mcbs

[whatif]

As I understand it, if disconnection times are met, older consumer units with rewireable fuses are ok. I know mcbs are faster, but what other meaningful advantages are there?

 

[andy]

resetable. means u dont need to use a nail as fusewire

 

[kai]

MCB's are safer - as there is no risk of burnt fingers if you re-set one against a fault, it will trip out very fast again, often before you have the chance to move the lever back up all the way.

It happened to me once, when I tried to reset a Wylex 16amp MCB against a fault, it immediately tripped again, leaving my finger unharmed.

 

[Lectrician]

happens to sparks all the time - LOL.

An MCB cant be abused - cant install a bigger fuse or wire. More convenient when it does 'blow'.

 

[kendor]

happens to sparks all the time - LOL.

An MCB cant be abused - cant install a bigger fuse or wire. More convenient when it does 'blow'.

Not completely true, I've spent ages trying to convince the management that they shouldn't have breakers as the means of isolation and that they are purely a protective device but my advice still goes by the wayside and the breakers are used to switch equipment on and off each day.
With no faults on a particular circuit, a Fuse will age with time and lose it's rating MCB's are more reliable in this case.

 

[AdamW]

When I was at school my form room was a Physics lab. There was an MCB/RCBO type breaker at the front of the room for all the sockets on desks. It was fun to fiddle with. Just press the test button and reset... or even (as I once tried) isolate the room, shove some scissors from live to neutral, go over to the breaker and switch it on again. Do tests count as trips with MCBs? If so, then schoolboy fiddling surely reduced the useful life of the device.

The only thing I have against breakers in a domestic situation is that people are more likely to investigate the problem if they have the inconvenience of rewiring a fuse to get the lights back on.

 

[plugwash]

happens to sparks all the time - LOL.

An MCB cant be abused - cant install a bigger fuse or wire. More convenient when it does 'blow'.

Not completely true, I've spent ages trying to convince the management that they shouldn't have breakers as the means of isolation and that they are purely a protective device but my advice still goes by the wayside and the breakers are used to switch equipment on and off each day.

When the green flag below the dolly is visible, then a contact gap of 4 mm has been achieved. Contactum MCBs may therefore be used as single pole isolating switches where appropriate.

so just what is the problem with using mcbs for switching?

 

[kendor]

When the green flag below the dolly is visible, then a contact gap of 4 mm has been achieved. Contactum MCBs may therefore be used as single pole isolating switches where appropriate.

so just what is the problem with using mcbs for switching?

Is this a case of a retailer trying to ply their wares with misleading info?
Unless things have changed the Regs were specific that protective devices were not to be used for isolation. I can understand this as the device will be put to mechanical stress of wear and tear which may affect it's performance as a protective device.

 

[Lectrician]

An isolator does NOT have to switch off on load. It could be a device for 'dry' switching only. Not much 'wear and tear' there.

I wouldn't use an MCB as a functional switch, thats daft.

I will always install isoltor SWITCHES for appliances.

You dont install an isolator for an entire circuit do you? And these DO need to be isolated from time to time aswell. The MCB is the isolator for that.

 

[kai]

That is why people install (or should do), a 13amp Fuse Connection Unit beside fixed appliances like immersion heaters, or washing machines etc.
or a Cooker /Shower Switch beside the Cooker/Shower.

 

[andy]

were my mam used 2 work the CU was next to the door. everything would be switched off (apart form the alarm) on a nighttime and switched back on in the morning

 

[ban-all-sheds]

When the green flag below the dolly is visible, then a contact gap of 4 mm has been achieved. Contactum MCBs may therefore be used as single pole isolating switches where appropriate.

so just what is the problem with using mcbs for switching?

Is this a case of a retailer trying to ply their wares with misleading info?
Unless things have changed the Regs were specific that protective devices were not to be used for isolation. I can understand this as the device will be put to mechanical stress of wear and tear which may affect it's performance as a protective device.

I think you're both right - the operative phrase is "where appropriate", so if an appliance needs to be isolated infrequently for maintenance or whatever, then the MCB can be appropriate for that. It would not be appropriate to use it for functional switching, or regular (e.g. at night) isolation.

 

[ban-all-sheds]

OOI - how many of you turn off all the non-essential circuits in your house when you go away on holiday?

 

[AdamW]

I have rewireable fuses so isolating seems to be a bit more of a task than flicking an MCB switch so I don't pull the fuses.

I switch off my immersion, shower pump, and everything bar the fridge at the plug sockets.

I always isolate my oven at the cooker switch after the cooldown phase has finished, I picked that habit up off someone else who always does it. It annoys me that I do it, but I still do.

 

[Damocles]

No a 32A breaker is not designed to break a current of 32A, it is designed to break a current of 1000A or so when fault current is flowing.