ANSI/IEEE Device Numbers. Protective relays are commonly referred to by standard device numbers. For example, a time overcurrent relay is designated a 51 device, while an instantaneous overcurrent is a 50 device. Multifunction relays have combinations of device numbers. A 27/59 device, for example, is a combination under/over voltage relay.
At 0Â° Celsius the speed of sound in U.S. textbooks is 331.3 m/s. At 20Â° Celsius the speed of sound then is 343.21 m/s, rounded 343 m/s. At 0Â° Celsius, the speed of sound in German textbooks is 331.5 m/s. At 20Â° Celsius the speed of sound then is 343.42 m/s, rounded 343 m/s.
The speed of sound is the rate of travel of a sound wave through an elastic medium. In dry air at 20 Â°C (68 Â°F), the speed of sound is 343 meters per second (1,125 ft/s). Thâ¦is equates to 1,236 kilometers per hour (768 mph), or about one kilometer in three seconds and about one mile in five seconds.