Nidec DFS Series Power Installation Manual

44 DFS1/DFS2 Power Installation GuideIssue Number: 24.15 Ground leakageSuitable measures include either a fixed ground connection or automatic disconnection of the supplyin case of discontinuity of the protective earthing conductor.4.16 Use of a residual current device (RCD)There are three common types of ELCB / RCD:• AC - detects AC fault currents• A - detects AC and pulsating DC fault currents (provided the DC current reaches zero at leastonce every half cycle)• B - detects AC, pulsating DC and smooth DC fault currentsType AC should not be used with variable speed drives.Type A can only be used with single phase drivesType B is the only type suitable for use with three phase, variable speed drivesIf an external EMC filter is used, a delay of at least 50 ms should be incorporated to prevent spurioustripping. The leakage current is likely to exceed the trip level if all phases are not energizedsimultaneously.4.17 Starts per hourThe number of starts per hour under electronic control is unlimited.The number of starts per hour caused by interrupting the AC supply is limited to 20 per hour equallyspaced (A minimum interval of 3 minutes between successive starts).4.18 Start-up timeThe time from the instant that power is applied to the drive being ready to run the motor is amaximum of 5 seconds4.19 Motor winding voltageThe drive output voltage can adversely affect the inter-turn insulation in the motor. This is because ofthe high rate of change of voltage, in conjunction with the impedance of the motor cable and thedistributed nature of the motor winding.For normal operation with AC supplies up to 500 Vac and a standard motor with a good qualityinsulation system, there is no need for any special precautions. In case of doubt, the motor suppliershould be consulted.Ground leakageThe ground leakage current is > 3.5 mA AC (10 mA DC).A permanent fixed ground connection must be provided, or other suitable measures takento prevent a safety hazard occurring if the connection is lost.RCD typesOnly type B ELCB / RCD are suitable for use with 3 phase inverter drives.WARNINGNOTEWARNINGNOTE