How Capacitors Work
Capacitors are similar in a way to batteries, but have different construction and characteristics. They store electric energy and release it when necessary; but unlike batteries, capacitors can be charged and discharged with a much higher frequency and may experience multiple charge-discharge cycles during operation. However, capacitors have one great disadvantage compared to batteries: they cannot retain electric energy for long periods of time.
Of all electronic components, aside from resistors, the construction of capacitors is one of the most simple. Basically they consist of two metallic plates brought in close proximity and isolated from one another with a dielectric substance, such as air, paper, mica, Teflon and others. The type of material used as dielectric depends on the application. For example, some dielectric material may behave well under high voltages and frequencies but may fail to work at ultra frequencies and low voltages. You can easily identify the symbol of the capacitor in electronic schematics, as it is represented by two parallel lines connected in the electronic circuit through terminals attached to each other. Capacitors may be polarized or non-polarized, meaning that the terminals are either positive or negative and must be connected in the electronic circuit accordingly.
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A solution to the socket shortage?
As a survey reveals two-thirds of Britons say they don't have enough plug sockets in their homes, what's the answer: messy multi-plug extension boards, more outlets, wireless electricity even? There's the telly. And the set-top box. The DVD player - although not the little-used video recorder, which now gathers dust in the attic - and the stereo and table lamp... that's at least five plugs clustered in one corner of a living room, and just a double socket to feed them all.
The solution? Increasingly, these days, it's a multi-plug extension board. These rat's nests of converging cables can be found around the home. Got a computer? That's a plug needed for (deep breath) the monitor, hard drive, printer, speakers, scanner and router. This hi-tech tangle is a bug bear of domestic life, especially for those living in Britain's vast stock of Victorian and Edwardian homes, when even the radio had yet to be invented. But new-builds account for just 160,000 houses a year of the UK's 25 million existing homes. In a survey for Energy Experience, an online education resource, 92% of respondents said their household used an average of three extension boards.
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Options in selecting the right circuit breaker
Choosing the right type of residual current circuit breaker is an important element in ensuring protection from electric shocks. Andy Scragg, Product Marketing Manager at Siemens Automation & Drives discusses selecting the right circuit breaker Making the right choices in electrical safety can mean the difference between life and death. This article was originally published on Electronicstalk on 9 Oct 2001 at 8.00am (UK)
Motor drives get rolling roads running.
Automotive equipment supplier Cirrus Technologies has teamed up with Siemens Automation and Drives to produce a new generation of rolling roads for use in end of line manufacturing applications. Choosing the right type of residual current circuit breaker is an important element in ensuring protection from electric shocks. Several factors have to be borne in mind when choosing the right device, particularly the way the breaker operates. The two most common types of residual current circuit breaker in use in the UK are voltage dependent and voltage independent residual current circuit breakers (RCCBs).
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Circuit-breaker detects all types of fault currents
The new universal-current-sensitive Type B residual-current circuit-breaker (r.c.c.b.) from Siemens Automation and Drives (A&D) can detect pulsating and smooth DC fault currents as well as sinusoidal AC fault currents. These new circuit-breakers are designed for rated currents of 25 to 80 A. Thanks to its tripping range, the r.c.c.b. is also suitable for applications in which medical protection must be guaranteed against dangerous ventricular fibrillation. Typical areas of application for the universal-current-sensitive Type B residual-current circuit-breaker include medical equipment, machine tools, charging stations, test systems, and laboratory equipment.
With the Type B residual-current circuit-breaker (r.c.c.b.), Siemens A&D offers a "universal-current-sensitive" circuit breaker. This circuit-breaker is suitable for plants in which smooth DC fault currents can occur as well as AC fault currents and pulsating fault currents. In this, it goes beyond the performance range of its predecessor, the Type A r.c.c.b. Smooth DC fault currents occur, for example, when operating frequency converters in cranes, machine controllers, elevator systems, and also in medical equipment such as computer tomographs.
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Counterfeit Circuit Breakers Recalled Due to Fire Hazard
The counterfeit circuit breakers are black and are labeled as Square D QO-series models 115, 120, 130, 215, 220, 230, 240, 250, 260 and 2020 and Square D QOB-series models 115, 120, 130, 220, 230, 250, 260 and 1515. Actual Square D circuit breakers have (a) the amp rating written on the handle in white paint on the front of the breaker (authentic Square D circuit breakers manufactured prior to 2003 did not have white paint on the amperage numbers); (b) the Square D insignia molded onto the breaker side, and; (c) a yellow chromate mounting clip with half of the top of the clip visible. If your breaker, labeled as Square D, does not match this description, it could be counterfeit.
The U.S. Consumer Product Safety Commission, in cooperation with Specialty Lamp International, Inc., has issued a voluntary recall of approximately 371,000 counterfeit "Square D" circuit breakers, due to a fire hazard. The circuit breakers can fail to trip when they are overloaded, and have been determined by Square D to be counterfeit. The counterfeit black circuit breakers were manufactured in China and sold by electrical product distributors from May 2005 through June 2006 for between $3 and $23. Please see the CPSC press release for model numbers involved in the recall.
