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.
In air, for example, the speed of sound increases with an increase in temperature. At 32 Â°F. (0 Â°C.), the speed of sound in air is 1,087 feet per second (331 m/s); at 68 Â°F. (20 Â°C.), it is 1,127 feet per second (343 m/s).