30mA trips versus fuses

[lebesset]

it used to be that the fuse box [ ok , consumer unit ] in your house contained fuses ; not only did they 'blow' if there was a short , they did so if you overloaded the circuit above the capacity of the wiring, fuse overheated and ....poof

now we commonly have the far better high sensitivity trips; question is , do they 'trip' if you overload the circuit as well as if there is a short , eg I have a ring main with 6 13 amp sockets , if I plug in 6 13 amp appliances that is above the rating for the cable ...what happens?

[Tweed]

I think you've got your wires crossed a bit. A short circuit will cause an overload. Fuses blow when a current above their rating flows through it. An MCB (minature circuit breaker) have replaced these and do the same job. A trip will fail when there is a current leakage usually to earth. It will not trip for a high current (overload/short circuit). Trip switches and fuses/circuit breakers are different devices for different types of fault.

[tomd]

A short circuit will cause a overload - the 'trip switch' will see them as one and the same.

Plugging 6x13 amps should trip the breaker - as long as it's rated properly, to match the cable.

[lebesset]

thanks for the responses , but if you read my post again , I am not interested in shorts , only in overloading a circuit

if you note I refer to 30mA trips , ie rccb's ; so that if I replace a fuse or mcb with a rccb of the same rating [ to match the wiring] , will it trip in the same way ?
ring mains are my prime concern as the wiring could be overloaded , a 32 amp mcb or fuse won't allow an overload , will a rccb?

[homer75]

rcd is faster both will trip when overloaded rcd used when trip speed is important eg electric shower

[Tweed]

An RCB has a rating in amps which is the highest current it can handle, and a rating in mAmps which is the current that will cause it to trip, i.e. if there's a difference of 30mA for example, between the positive and negative it will trip. These should be the same and if they're not then there is a current leakage somewhere. An RCB will not protect you against overload. That's what a fuse and MCB are for. You can't replace an MCB with an RCB as they are different devices for different types of potential faults.