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The neutral conductor of a 3-phase, 4-wire system and the middle conductor of a 2- phase, 3-wire system must have at least 2 separate and distinct earth connections with a minimum of 2 different earth electrodes to have a satisfactory earth resistance; The earth electrodes must be interconnected to reduce earth resistance
The international standard IEC 60446 Basic and safety principles for man-machine interface, marking and identification - Identification of equipment terminals, conductor terminations and conductors was a standard published by the International Electrotechnical Commission (IEC) that defined basic safety principles for identifying electrical conductors by colours or numerals, for example in ...
For power circuits, the color-coding uses the same colors as residential construction, and adds the additional wires used for three-phase systems. Black, Red and Blue are used for hot wires and White is used as the neutral wire in a 120/208 V circuit. Brown, Orange and Yellow are used as hot wires and gray is used as the neutral wire in a 277/ ...
A 2.26 kΩ, 1%-precision resistor with 5 color bands (), from top, 2-2-6-1-1; the last two brown bands indicate the multiplier (×10) and the tolerance (1%).. An electronic color code or electronic colour code (see spelling differences) is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others.
For very large currents in generating stations or substations, where it is difficult to provide circuit protection, an isolated-phase bus is used. Each phase of the circuit is run in a separate grounded metal enclosure. The only fault possible is a phase-to-ground fault, since the enclosures are separated.
Long-distance electromagnetic telegraph systems from 1820 onwards [a] used two or more wires to carry the signal and return currents. It was discovered by German scientist C.A. von Steinheil in 1836–1837, that the ground could be used as the return path to complete the circuit, making the return wire unnecessary. [2]
One voltage cycle of a three-phase system. A polyphase system (the term coined by Silvanus Thompson) is a means of distributing alternating-current (AC) electrical power that utilizes more than one AC phase, which refers to the phase offset value (in degrees) between AC in multiple conducting wires; phases may also refer to the corresponding terminals and conductors, as in color codes.
For example, balanced two-phase power can be obtained from a three-phase network by using two specially constructed transformers, with taps at 50% and 86.6% of the primary voltage. This Scott T connection produces a true two-phase system with 90° time difference between the phases.