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The supply circuit breaker has to protect not just the cables in the wall, but also the flexible cords to the appliances.

If you had 50A circuit breakers, the appliance cords would have to be rated to carry the higher fault current in the event of a short-circuit. The fault current would be several times 50A, but usually for a short time, depending on the time-current curve of the circuit breaker and the imepdance in the circuit.

This would mean that appliance cords would be thick, inflexible, and expensive.

In the UK we have 32A socket circuits, but our plugs contain fuses at 3A or 13A depending on the appliance rating. Therefore the appliance cords only need to be rated for 3A. (Actually, all modern appliance cords have to be rated for 16A for EU compatability, as other EU countries have 16A socket on 16A or 20A circuits, and unfused plugs. The appliance cords are usually quite short, so the impedance is low and a high-enough fault current flows to quickly trip the breaker before the cord gets too hot and is damaged.)

In 'the olden days' the UK had unused plugs, with protection provided at the fuseboard by rewireable fuse-wire. Sockets were 2A (table lights), 5A (small appliances, kettles etc to 1200 watts), and 15A (heaters to 3kW). This was inconvenient as you couldn't (safely) plug a 2A appliance into a 15A socket. A variety of adapters of varying lethality existed.

After World War Two, the development of the fused 13A plug with its high-rupture capacity sand-filled cartridge fused meant that a fused 13A plug could provide suitable protection to an existing small appliance. Because the plug is fused to protect the appliance, and the circuit is fused at 32A to protect the fixed wiring, we can have many sockets on one circuit due to the principle of diversity. This was a considerable saving in copper wire and labour, both of which were in short supply after the War. A typical 3-4 bedroom house will have three socket circuits - upstairs, downstairs, and kitchen/utility room. 20 or 30 sockets on each circuit would not be unusual and there is no overload as most of them are used for low-current appliances (TV, phone chargers, etc).

Only cookers ranges and instantaneous showers are given their own higher-current circuits, but it's usual to provide a separate 16A circuit for a 3kW immersion water heater if used.

In conclusion, 15-20 amp plugs are the largest that are convenient for everyday use. Smaller plugs would be insufficient for heating appliances (especially on 110 volts) and larger ones would be inconvenient and expensive.

13 amp plug image from http://plugwiring.co.uk/how-to-wire-a-plug/

fuses image from http://plugwiring.co.uk/plug-wiring-posts/choosing-the-correct-fuse-for-an-appliance-with-a-bs-1363-type-plug/

The supply circuit breaker has to protect not just the cables in the wall, but also the flexible cords to the appliances.

If you had 50A circuit breakers, the appliance cords would have to be rated to carry the higher fault current in the event of a short-circuit. The fault current would be several times 50A, but usually for a short time, depending on the time-current curve of the circuit breaker and the imepdance in the circuit.

This would mean that appliance cords would be thick, inflexible, and expensive.

In the UK we have 32A socket circuits, but our plugs contain fuses at 3A or 13A depending on the appliance rating. Therefore the appliance cords only need to be rated for 3A. (Actually, all modern appliance cords have to be rated for 16A for EU compatability, as other EU countries have 16A socket on 16A or 20A circuits, and unfused plugs. The appliance cords are usually quite short, so the impedance is low and a high-enough fault current flows to quickly trip the breaker before the cord gets too hot and is damaged.)

In 'the olden days' the UK had unused plugs, with protection provided at the fuseboard by rewireable fuse-wire. Sockets were 2A (table lights), 5A (small appliances, kettles etc to 1200 watts), and 15A (heaters to 3kW). This was inconvenient as you couldn't (safely) plug a 2A appliance into a 15A socket. A variety of adapters of varying lethality existed.

After World War Two, the development of the fused 13A plug with its high-rupture capacity sand-filled cartridge fused meant that a fused 13A plug could provide suitable protection to an existing small appliance. Because the plug is fused to protect the appliance, and the circuit is fused at 32A to protect the fixed wiring, we can have many sockets on one circuit due to the principle of diversity. This was a considerable saving in copper wire and labour, both of which were in short supply after the War. A typical 3-4 bedroom house will have three socket circuits - upstairs, downstairs, and kitchen/utility room. 20 or 30 sockets on each circuit would not be unusual and there is no overload as most of them are used for low-current appliances (TV, phone chargers, etc).

Only cookers ranges and instantaneous showers are given their own higher-current circuits, but it's usual to provide a separate 16A circuit for a 3kW immersion water heater if used.

13 amp plug image from http://plugwiring.co.uk/how-to-wire-a-plug/

fuses image from http://plugwiring.co.uk/plug-wiring-posts/choosing-the-correct-fuse-for-an-appliance-with-a-bs-1363-type-plug/

The supply circuit breaker has to protect not just the cables in the wall, but also the flexible cords to the appliances.

If you had 50A circuit breakers, the appliance cords would have to be rated to carry the higher fault current in the event of a short-circuit. The fault current would be several times 50A, but usually for a short time, depending on the time-current curve of the circuit breaker and the imepdance in the circuit.

This would mean that appliance cords would be thick, inflexible, and expensive.

In the UK we have 32A socket circuits, but our plugs contain fuses at 3A or 13A depending on the appliance rating. Therefore the appliance cords only need to be rated for 3A. (Actually, all modern appliance cords have to be rated for 16A for EU compatability, as other EU countries have 16A socket on 16A or 20A circuits, and unfused plugs. The appliance cords are usually quite short, so the impedance is low and a high-enough fault current flows to quickly trip the breaker before the cord gets too hot and is damaged.)

In 'the olden days' the UK had unused plugs, with protection provided at the fuseboard by rewireable fuse-wire. Sockets were 2A (table lights), 5A (small appliances, kettles etc to 1200 watts), and 15A (heaters to 3kW). This was inconvenient as you couldn't (safely) plug a 2A appliance into a 15A socket. A variety of adapters of varying lethality existed.

After World War Two, the development of the fused 13A plug with its high-rupture capacity sand-filled cartridge fused meant that a fused 13A plug could provide suitable protection to an existing small appliance. Because the plug is fused to protect the appliance, and the circuit is fused at 32A to protect the fixed wiring, we can have many sockets on one circuit due to the principle of diversity. This was a considerable saving in copper wire and labour, both of which were in short supply after the War. A typical 3-4 bedroom house will have three socket circuits - upstairs, downstairs, and kitchen/utility room. 20 or 30 sockets on each circuit would not be unusual and there is no overload as most of them are used for low-current appliances (TV, phone chargers, etc).

Only cookers ranges and instantaneous showers are given their own higher-current circuits, but it's usual to provide a separate 16A circuit for a 3kW immersion water heater if used.

In conclusion, 15-20 amp plugs are the largest that are convenient for everyday use. Smaller plugs would be insufficient for heating appliances (especially on 110 volts) and larger ones would be inconvenient and expensive.

13 amp plug image from http://plugwiring.co.uk/how-to-wire-a-plug/

fuses image from http://plugwiring.co.uk/plug-wiring-posts/choosing-the-correct-fuse-for-an-appliance-with-a-bs-1363-type-plug/

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source | link

The supply circuit breaker has to protect not just the cables in the wall, but also the flexible cords to the appliances.

If you had 50A circuit breakers, the appliance cords would have to be rated to carry the higher fault current in the event of a short-circuit. The fault current would be several times 50A, but usually for a short time, depending on the time-current curve of the circuit breaker and the imepdance in the circuit.

This would mean that appliance cords would be thick, inflexible, and expensive.

In the UK we have 32A socket circuits, but our plugs contain fuses at 3A or 13A depending on the appliance rating. Therefore the appliance cords only need to be rated for 3A. (Actually, all modern appliance cords have to be rated for 16A for EU compatability, as other EU countries have 16A socket on 16A or 20A circuits, and unfused plugs. The appliance cords are usually quite short, so the impedance is low and a high-enough fault current flows to quickly trip the breaker before the cord gets too hot and is damaged.)

In 'the olden days' the UK had unused plugs, with protection provided at the fuseboard by rewireable fuse-wire. Sockets were 2A (table lights), 5A (small appliances, kettles etc to 1200 watts), and 15A (heaters to 3kW). This was inconvenient as you couldn't (safely) plug a 2A appliance into a 15A socket. A variety of adapters of varying lethality existed.

After World War Two, the development of the fused 13A plug with its high-rupture capacity sand-filled cartridge fused meant that a fused 13A plug could provide suitable protection to an existing small appliance. Because the plug is fused to protect the appliance, and the circuit is fused at 32A to protect the fixed wiring, we can have many sockets on one circuit due to the principle of diversity. This was a considerable saving in copper wire and labour, both of which were in short supply after the War. A typical 3-4 bedroom house will have three socket circuits - upstairs, downstairs, and kitchen/utility room. 20 or 30 sockets on each circuit would not be unusual and there is no overload as most of them are used for low-current appliances (TV, phone chargers, etc).

Only cookers ranges and instantaneous showers are given their own higher-current circuits, but it's usual to provide a separate 16A circuit for a 3kW immersion water heater if used.

13 amp plug image from http://plugwiring.co.uk/how-to-wire-a-plug/

fuses image from http://plugwiring.co.uk/plug-wiring-posts/choosing-the-correct-fuse-for-an-appliance-with-a-bs-1363-type-plug/