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One form of fuse box abuse was to put a penny in the socket, Shortest which defeated overcurrent protection and resulted in a dangerous condition. Some manufacturers of medium-voltage distribution fuses combine the overcurrent protection characteristics of the fusible element with the flexibility of relay protection by adding a pyrotechnic device to the fuse operated by external protective relays. In terms of protection response time, fuses tend to isolate faults more quickly (depending on their operating time) than circuit breakers. On the other hand, replacing a fuse without isolating the circuit first (most building wiring designs do not provide individual isolation switches for each fuse) can be dangerous in itself, particularly if the fault is a short circuit. A fuse can clear a fault within a quarter cycle of the fault current, while a circuit breaker may take around half to one cycle to clear the fault. Appliances that run on 220 volts must have a higher resistance so that they take less current to use the same amount of power as they would on 110volts. 220 volts connected to a 110 volts appliance would result in 4 times the power ending up in the appliance (because voltage is double and current is double), likely burning out the appliance.

Renewable fuses (rewirable or cartridge) allow user replacement, but this can be hazardous as it is easy to put a higher-rated or double fuse element (link or wire) into the holder (overfusing), or simply fitting it with copper wire or even a totally different type of conducting object (coins, hairpins, paper clips, nails, etc.) to the existing carrier. Thanks for info, I think I will investigate double isolated transformers more. Pole-mounted distribution transformers are nearly always protected by a fusible cutout, which can have the fuse element replaced using live-line maintenance tools. All fuses of different technologies tested to meet IEC standards will have similar time-current characteristics, which simplifies design and maintenance. In the United States and Canada, low-voltage fuses to 1 kV AC rating are made in accordance with Underwriters Laboratories standard UL 248 or the harmonized Canadian Standards Association standard C22.2 No. 248. This standard applies to fuses rated 1 kV or less, AC or DC, and with breaking capacity up to 200 kA. UL 248 currently has 19 "parts". UL 248-1 sets the general requirements for fuses, while the latter parts are dedicated to specific fuses sizes (ex: 248-8 for Class J, 248-10 for Class L), or for categories of fuses with unique properties (ex: 248-13 for semiconductor fuses, 248-19 for photovoltaic fuses).

Dimensions are chosen to provide safe clearance to live parts. Since power lines are designed for long-term use, Kelvin's law is used in conjunction with long-term estimates of the price of copper and aluminum as well as interest rates. Like standard NM cable, UF contains insulated hot and neutral wires, plus a bare copper ground wire. Large power fuses use fusible elements made of silver, copper or tin to provide stable and predictable performance. The Electric Power Engineering Handbook. To reduce the risk of users accidentally touching energized conductors and thereby experiencing electric shock, plug and socket systems often incorporate safety features in addition to the recessed contacts of the energized socket. Distinctive characteristics of the system are shutters on the line and neutral socket holes, what are electric cables and a fuse in the plug. BS 546:1934 clause 2 specifies interchangeability with BS 372 Part II which includes the same four plug and socket sizes. There are four ratings of plug and socket in BS 546, (2 A, 5 A, 15 A and 30 A).

Fuses have the advantages of often being less costly and simpler than a circuit breaker for similar ratings. The standard ampere ratings for fuses (and circuit breakers) in USA/Canada are considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. These fuses open in less than one cycle of the AC power frequency; circuit breakers cannot match this speed. Medium-voltage fuses are also used to protect motors, capacitor banks and transformers and may be mounted in metal enclosed switchgear, or (rarely in new designs) on open switchboards. Stepdown transformers located near equipment shelters provide operating power for the shelters. High-voltage fuses are used to protect instrument transformers used for electricity metering, or for small power transformers where the expense of a circuit breaker is not warranted.