Fuses and circuit breakers Fuses and circuit breakers protect electrical circuits and appliances. Fuses The fuse breaks the circuit if a fault in an appliance causes too much current to flow. A 13A fuse contains a low melting point wire Fuses in plugs are made in standard ratings.
The fuse should be rated at a slightly higher current than the device needs: if the device works at 3 A, use a 5 A fuse if the device works at 10 A, use a 13 A fuse Circuit breakers Circuit breakers act as resettable fuses. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit. Residual Current Devices or RCDs are designed to detect and disconnect supply in the event of an earth fault, for example when a live conductor touches an earthed equipment case, or when a live conductor is cut through.
This type of fault is potentially dangerous and can result in electric shocks and fires. A Miniature Circuit Breaker is an electromechanical device designed to protect an electric circuit from overcurrent. MCBs are reusable where fuses are not. There are much more expensive than fuses, and require regular testing. Ambient temperature also affects their performance. If the appliance has 0. These rating figures are determined by the temperature the cable may reach in operation. The fuse size is determined by using a "non-adiabatic" method, looking at whether the cable will overheat in a direct short-circuit.
The only limits on flex length apart from 0. So, how does this relate to your tin opener? So he chooses 0. Then needs to size fuse, and again refers to Table 2 of BS which says that 0. Manufacturer then ensures with the aid of the appliance safety standard - in this case the appropriate parts of BS EN, I'd guess that the tin opener will not cause fire or shock or burns in a fault with the selected fuse let-through, and presto - design complete. It is only through Grahams explanation that it makes any sense to me at all.
I've always thought it was better to use as low a fuse as possible because i was led to belive the fuse was added protection to the user in the event of a fault, but i see this is -strictly speaking- not the case.
Oh well. New here? To participate in discussions, please log in and introduce yourself. Shift Technician. Senior Engineer- Systems Architect. Recruiter: Telent Apply for this job. Understanding the logic behind my answer may help to identify anomalies and also explain some odd choices of fuse you may come across on a day today basis. Always comply with any regulation or law that applies in your country or region. If unsure, consult a qualified electrician. What do fuses protect? So the question remains, what do fuses protect?
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