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In both those instances the white wire should be identified as being hot, usually with black tape inside junction boxes. The neutral wire is identified by gray or white insulated wire, perhaps using stripes or markings. With lamp cord wire the ribbed wire is the neutral, and the smooth wire is the hot. NEC 2008 400.22(f) allows surface marking ...
The VLF cable testing time varies from 15 to 60 minutes. IEEE 400.2 establishes some suggested test voltages and times. Subsequent work by the CDFI has shown there to be no significant change in the efficacy of a VLF test conducted over the frequency range 0.1 to 0.01 Hz when the IEEE 400.2 voltages and times are used. [2]
IEC 60657 Non-ionizing radiation hazards in the frequency range from 10 MHz to 300 000 MHz; IEC 60660 Insulators – Tests on indoor post insulators of organic material for systems with nominal voltages greater than 1 000 V up to but not including 300 kV; IEC 60661 Methods for measuring the performance of electric household coffee makers
for AC having a supply frequency of 50, 60 or 400Hz, though the use of other frequencies for special purposes is not excluded. This includes low-voltage installations, as found in most domestic and commercial properties, and extra-low-voltage systems, but excludes high voltage , as found in generation, transmission and distribution networks.
In fixed wiring, the blue/brown scheme is only found in newer (post-2004) installations, and the old IEE red/black scheme is likely to be encountered in existing installations for many more decades. Earlier in the 20th century, green and blue were used as a neutral alongside black, which became the only neutral colour from 1943.
A full-load wire does heat up slightly due to the metallic resistance of the wire, but this wire heating is factored into the cable's temperature rating. (NEC 310.10) [12] The NEC specifies acceptable numbers of conductors in crowded areas such as inside conduit, referred to as the fill rating.
Differences in voltage may give rise to compatibility issues, especially for travellers and those purchasing appliances overseas or online. Most 230 V equipment will work with a supply voltage in the range 220–240 V without issues. The mains frequency is 50 Hz in all these countries.
The voltage and frequency of electric power differs between regions. In much of the world, a voltage (nominally) of 230 volts and frequency of 50 Hz is used. In North America, the most common combination is 120 V and a frequency of 60 Hz. Other combinations exist, for example, 230 V at 60 Hz.