GB 50052-2009 第3.5.3条
| In a TN system, when the overcurrent protective device of a distribution circuit also serves as earth-fault protection, the fault circuit shall be disconnected within the specified time, and the operating characteristics of the protective device shall comply with: Zs·Ia ≤ U0·2/3 (where Zs is the earth-fault loop impedance, Ia is the operating current of the protective device, and U0 is the phase voltage).