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VA ratings are also often used for transformers; maximum output current is then VA rating divided by nominal output voltage. [5] Transformers with the same sized core usually have the same VA rating. The convention of using the volt-ampere to distinguish apparent power from real power is allowed by the SI standard. [6] [page needed]
For AC-operated devices (e.g. coaxial cable, loudspeakers), there may even be two power ratings, a maximum (peak) power rating and an average power rating. [5] [6] For such devices, the peak power rating usually specifies the low frequency or pulse energy, while the average power rating limits high-frequency operation. [5]
For an electric machine, the power rating is the number on its rating plate and corresponds to a maximum electric load it can carry. There is a distinction between the continuous rating (for generators, continuous maximum rating or CMR [ 2 ] ), at which the machine can be operational without a time limit and short-term rating that can only be ...
For example, types 3, 4 and 6 are intended for outdoor use, but type 5 is not. A NEMA enclosure rating does not mean that it also meets the same UL enclosure rating. [2] NFPA is National Fire Protection Association, and NEC is National Electrical Code (U.S.A.)
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Real-time ratings allow control room engineers to adjust power flows according to normal operational events or contingencies. They are based on "steady-state (equilibrium) ampacity" calculations. Emergency ratings are based on transient equations and models: they provide permissible overload ratings for a short and adjustable time (typically 5 ...
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According to the National Christmas Tree Association, most Christmas trees need about 7 to 10 years to reach the ideal height for decorating, which is typically around 6 or 7 feet.