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A hunk of copper is visible that is designed to be easily connected or disconnected from its place between two screws, rated for 600 A (as stamped on it). We also see the thick wires in standard colors (two yellow/green ground and two blue neutral), as well as markings PEN (protected earth and neutral), PE (protective earth) and N (neutral).
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 277/480 V. For grounding, regardless of the voltage, Green (or a bare wire) is used.
A somewhat similar system called "concentric wiring" was introduced in the United States around 1905. In this system, an insulated electrical wire was wrapped with copper tape which was then soldered, forming the grounded (return) conductor of the wiring system. The bare metal sheath, at earth potential, was considered safe to touch.
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 ...
The National Electric Code (NEC) only specifies colors for ground and neutral: Green for the equipment grounding (safety) conductor (NEC Article 250.119), and white or grey for the neutral (grounded) conductor (NEC Article 200.6). These colors may not be used for any other purpose, nor may their purpose use a different color.
Per UL Standard ANSI/UL 498, a receptacle (any color) with an orange triangle, is an isolated ground (IG) device, where the grounding pin of the receptacle is connected to ground independently of the frame of the receptacle and wiring outlet box. This is also a requirement of the National Electrical Code (NFPA 70), Article 406.
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Mains electrical wiring, both in a building and on equipment, was once usually red for live, black for neutral, and green for earth, but this was changed as it was a hazard for color-blind people, who might confuse red and green; different countries use different conventions. Red and black are frequently used for positive and negative of ...