Are mains plug fuses really needed now?

Section62

grumbler said:

Section62 said:

grumbler said:

Risteard said:

grumbler said:

Risteard said:

MrsStepford said:

When I lived in Canada, the main itself was earthed, so none of the power sockets had switches or fuses, you just plugged them in. I was told that this is safer but I remain unconvinced. 

It's not necessary there or throughout most of the world because they don't have ring final circuits.

I think, it's an over-simplistic explanation. Why do we have, say, 5A fuses in some plugs?

And if this really were the case, it would make much more sense to have fuses in the sockets, not in the plugs.

It's not necessary there because there electrical safety standards are lower.

It's not overly simplistic - it's the simple fact of the matter.

I don't see any relation between ring circuits and fuses in plugs.

A ring final circuit is a system.

A requirement of installing a ring final circuit is the use of accessories (e.g. socket outlets) complying with BS1363.  BS1363 accessories are designed to use a fuse complying with BS1362.

Hence you can't (legally) install a domestic final ring circuit which doesn't make use of BS1362 fuses, either in the plugtop or in the accessory.

That is the simple fact of the matter.

The reason why is that in the UK (and some other countries) we have opted for a system using a higher capacity final circuit (e.g. designed for protection by a 30/32A fuse/MCB) with the required lower level of protection (e.g. 3A / 13A) located at the point the appliance connects to the final ring circuit.

Elsewhere in the world the final circuits are designed with a lower capacity and the protective device (e.g. 15 or 16A) is located at the consumer unit.  Hence they have no need for plugtop fuses because the consumer unit is providing the required level of protection.

Prior to the UK adopting the '13A plug', we used a similar domestic system involving unfused round-pin plugs of (generally) 2A, 5A or 15A capacity.  In theory these 15A plugs would be used with circuits protected by a 15A fuse at the consumer unit, 5A plugs on a circuit protected by a 5A fuse (quite often a spur from a lighting circuit).  The theory didn't really represent practice though, which is one of the reasons why the standardised system of BS1363 was introduced - all plugtops would be the same and could be used in any BS1363 socket, only the fuse rating needed to be correctly selected.

References to regulations and history don't support your original statement "because they don't have ring final circuits". At least I don't see any logic in this explanation and you didn't address the points I raised in my previous point.
"Elsewhere in the world" not all appliances have cables with 15A capacity, e.g. desk lamps. As a result,  15A devices located at the CU don't provide "the required level of protection". What's "required" and why "they have no need for [fused] plugtop"? My answer is  that it's because the requirements (safety standards) are different.

It wasn't my "original statement".

The fact you can't see the logic doesn't mean the logic isn't there and makes sense.  I get the feeling you are just looking for an argument with someone, so I'll leave it at that.

grumbler

Section62 said:

grumbler said:

Section62 said:

grumbler said:

Risteard said:

grumbler said:

Risteard said:

MrsStepford said:

When I lived in Canada, the main itself was earthed, so none of the power sockets had switches or fuses, you just plugged them in. I was told that this is safer but I remain unconvinced. 

It's not necessary there or throughout most of the world because they don't have ring final circuits.

I think, it's an over-simplistic explanation. Why do we have, say, 5A fuses in some plugs?

And if this really were the case, it would make much more sense to have fuses in the sockets, not in the plugs.

It's not necessary there because there electrical safety standards are lower.

It's not overly simplistic - it's the simple fact of the matter.

I don't see any relation between ring circuits and fuses in plugs.

A ring final circuit is a system.

A requirement of installing a ring final circuit is the use of accessories (e.g. socket outlets) complying with BS1363.  BS1363 accessories are designed to use a fuse complying with BS1362.

Hence you can't (legally) install a domestic final ring circuit which doesn't make use of BS1362 fuses, either in the plugtop or in the accessory.

That is the simple fact of the matter.

The reason why is that in the UK (and some other countries) we have opted for a system using a higher capacity final circuit (e.g. designed for protection by a 30/32A fuse/MCB) with the required lower level of protection (e.g. 3A / 13A) located at the point the appliance connects to the final ring circuit.

Elsewhere in the world the final circuits are designed with a lower capacity and the protective device (e.g. 15 or 16A) is located at the consumer unit.  Hence they have no need for plugtop fuses because the consumer unit is providing the required level of protection.

Prior to the UK adopting the '13A plug', we used a similar domestic system involving unfused round-pin plugs of (generally) 2A, 5A or 15A capacity.  In theory these 15A plugs would be used with circuits protected by a 15A fuse at the consumer unit, 5A plugs on a circuit protected by a 5A fuse (quite often a spur from a lighting circuit).  The theory didn't really represent practice though, which is one of the reasons why the standardised system of BS1363 was introduced - all plugtops would be the same and could be used in any BS1363 socket, only the fuse rating needed to be correctly selected.

References to regulations and history don't support your original statement "because they don't have ring final circuits". At least I don't see any logic in this explanation and you didn't address the points I raised in my previous point.
"Elsewhere in the world" not all appliances have cables with 15A capacity, e.g. desk lamps. As a result,  15A devices located at the CU don't provide "the required level of protection". What's "required" and why "they have no need for [fused] plugtop"? My answer is  that it's because the requirements (safety standards) are different.

It wasn't my "original statement".

The fact you can't see the logic doesn't mean the logic isn't there and makes sense.  I get the feeling you are just looking for an argument with someone, so I'll leave it at that.

My apologies, I thought I was replying to Risteard. It's his style to quote endless regulation like Bible. In this case this doesn't work for obviouse reason.
Does my reply make sense now? In his 'original statement' he used the word 'because' that does imply some logic, but I don't see any. If there really is some logic, I am happy to see an explanation from anybody, be it Ristead, you or anybody else.

Ectophile

Elsewhere in the world, they don't plug small houshold appliances directly into 32A circuits.  15A or 20A is more normal.  But after WW II, we needed to build a lot of new houses, using as few materials as possible.  Copper was one of the things in short supply.

Other countries use "radial circuits".  Each circuit is connected at one end to the consumer unit, and powers a limited number of sockets.  But someone in the UK realised that they could save copper by using one ring circuit to power every socket in the house.  But that would need a 30A fuse if it wasn't going to blow all the time.  However, plugging a table lamp into a 30A ring isn't very clever - one fault and the thin flex could go up in smoke.  So they specified a new rectangular pin 13A plug, and added a fuse to it.

These days, we use 32A breakers instead of fuses, and usually split the sockets across 2 or 3 circuits.  But we still use rings.  So we still have fuses in the plugs.

5A fuses aren't officially a standard size.  But you can get them, and they are widely used in appliances such as somputers, that use a 3-pin IEC "kettle" plug.  The common IEC plugs and sockets (not the neat resistant ones actually used on kettles) are only rated at 6A.  So the manufacturers put a 5A fuse in the plug.

markin

The socket would melt before the mcb would trip.