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Something basic - kWh
The kilowatt hour (symbol kWh, kW?h, or kW h) is a derived unit of energy equal to 3.6 megajoules. If the energy is being transmitted or used at a constant rate (power) over a period of time, the total energy in kilowatt-hours is the product of the power in kilowatts and the time in hours. The kilowatt-hour is commonly used as a billing unit for energy delivered to consumers by electric utilities.
The symbol "kWh" is commonly used in commercial, educational, scientific and media publications, and is the usual practice in electrical power engineering.
Other abbreviations and symbols may be encountered:
"kW h" is less commonly used. It is consistent with SI standards (but note that the kilowatt-hour is a non-SI unit). The international standard for SI states that in forming a compound unit symbol, "Multiplication must be indicated by a space or a half-high (centered) dot (?), since otherwise some prefixes could be misinterpreted as a unit symbol" (i.e., kW h or kW?h). This is supported by a voluntary standard6 issued jointly by an international (IEEE) and national (ASTM) organization. However, at least one major usage guide and the IEEE/ASTM standard allow "kWh" (but do not mention other multiples of the watt hour). One guide published by NIST specifically recommends avoiding "kWh" "to avoid possible confusion".
The US official fuel-economy window sticker for electric vehicles uses the abbreviation "kW-hrs".
Variations in capitalization are sometimes seen: KWh, KWH, kwh etc.
"kW?h" is, like "kW h", preferred with SI standards, but it is very rarely used in practice.
The notation "kW/h", as a symbol for kilowatt-hour, is not correct.
Źródło: https://en.wikipedia.org/wiki/Kilowatt_hour
How to ensure the client's professionalism?
Customers will always choose a reliable service provider. The case concerns not only the electrical services or painting, but virtually every area. Therefore, many providers may boast all sorts of references. If you employ an electrician, they are important as that incompetent employee can lead to much more serious consequences than, for example, inept painter. Therefore, references in this profession are highly desirable and through it you can easily build a stable authority among customers, which nowadays allows you to pause for more specific customer with the right electric guitar.
Wires - about colors
To enable wires to be easily and safely identified, all common wiring safety codes mandate a colour scheme for the insulation on power conductors. In a typical electrical code, some colour-coding is mandatory, while some may be optional. Many local rules and exceptions exist per country, state or region.1 Older installations vary in colour codes, and colours may fade with insulation exposure to heat, light and ageing.
As of March 2011, the European Committee for Electrotechnical Standardization (CENELEC) requires the use of green/yellow colour cables as protective conductors, blue as neutral conductors and brown as single-phase conductors.2 The United States National Electrical Code requires a green or green/yellow protective conductor, a white or grey neutral, and a black single phase.3
The United Kingdom requires the use of wire covered with green insulation, to be marked with a prominent yellow stripe, for safe earthing (grounding) connections.4 This growing international standard was adopted for its distinctive appearance, to reduce the likelihood of dangerous confusion of safety earthing (grounding) wires with other electrical functions, especially by persons affected by red-green colour blindness.
In the UK, phases could be identified as being live by using coloured indicator lights: red, yellow and blue. The new cable colours of brown, black and grey do not lend themselves to coloured indicators. For this reason, three-phase control panels will often use indicator lights of the old colours.
Źródło: https://en.wikipedia.org/wiki/Electrical_wiring#Colour_code