7. cascade with low-voltage distribution circuit breakers and circuit breaker when the circuit breaker for the use of short-circuit protection circuit breaker breaking capacity must be greater than the installation of the possible short-circuit current. But sometimes can not meet this requirement. For example: breaking capacity C45N, C65N / H miniature circuit breakers were only 6kA, 10kA Nanyang electrical engineering, but it is installed at the outlet end of the short-circuit current up to 15kA sometimes even higher. Available at this time two ways to resolve this problem, the first is to switch to a high short-circuit breaking capacity MCCB; the second is still the choice of miniature circuit breakers, with its cascade with the circuit breaker and superiors to achieve short-circuit protection. However, selection on the lower level with a cascade circuit breaker must meet the following conditions: 1) the prerequisite is inherently superior breaker breaking time is shorter than the lower full-breaker breaking. That is lower short circuit breaker outlet end, not enough time to cut off the lower short-circuit current, on a first cut off the short-circuit current. 2) lower the circuit breaker can not be cut short, although the current Nanyang power project to install, but the lower circuit breaker and is protected by lines should be able to withstand the short-circuit current. 3) should a power failure cut off the circuit leapfrog line outside a secondary load caused by interrupts. 4) on the lower breaker should adopt the same range of products, the rated current level difference between the best grade 1 to 2, or under the cascade with meter factory offers to choose. Now cascade Schneider Electric provided with tables attached. Thus table shows Nanyang power engineering maintenance, C65N / H circuit breakers with NS100, NS160, NS250 circuit breaker with cascade, can not meet with greater NS400, N630 and above the breaker, but can not be directly connected On the low voltage side of the transformer frame of the bus after the main switch low-voltage screen. Ground Connection and Zero range of applications suitable protective earth neutral grounding grid. Three-phase four-wire neutral grounding grid should be used to protect access to zero measures. Since all dielectric breakdown or other reasons may present a hazardous voltage metal parts should be taken to ground or zero. 1, should be taken to ground or zero devices 1) motors, transformers, electrical appliances, lighting equipment, portable and mobile electric appliances such as metal, base and gear attached thereto. 2) metal structures or reinforced concrete as well as indoor and outdoor power distribution unit near energized parts of the metal cover fence, fence or a metal gate. 3) distribution panel, console, console, control box of the metal frame or enclosure. 4) transformer secondary winding. 5) AC-DC power cable boxes metal, metal sheath of steel pipe and cable wiring. 6) fitted with a metal rod lightning line power lines and reinforced concrete tower. 7) mounted on Distribution Feeders switches, capacitors and other electrical equipment. Nanyang electric power engineering and maintenance, Fu Long electricity (certified), Nanyang Electrical Engineering offered by Nanyang Fu Long Electric Power Engineering Company Limited. Nanyang Fu Long Electric Power Engineering Co., Ltd. (www.nyfulong.com) is Nanyang, Henan, transmission equipment and materials leaders, over the years, the company is implementing the scientific management, innovation and development, the principle of honesty and trustworthiness, and satisfy customer needs. Teflon power in leadership with the staff warmly welcome all inquiries negotiations to create Teflon electricity better future.