2 Engineering2.12 Loading conditionsDS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com 532.12 Loading conditionsDS7 soft starters are designed for a standard duty cycle as defined forAC-53a in product standard IEC/EN 60947-2-1. This means:3-fold overcurrent for 5 seconds with a duty factor of 75 % and 10 startsper hour. For example: 4A: AC-53a: 3-5: 75-10With applications such as water pumps (circulating pumps) the DS7 softstarter with the assigned rated operational current can be selected. Whendifferent operating frequencies, acceleration and/or starting currents areinvolved, the thermal capacity of the DS7 soft starter must be taken intoaccount in the design.2.12.1 Overload capability (load to AC-53a)The table below shows the overload capability of the soft starter inaccordance with the product standard IEC/EN 60 947-4-2. It shows:X = Value of basic overcurrent in multiples of the rated device currentT x = Duration of the overcurrent X in secondsF = Duty factor within the load cycle in %S = Number of permissible starts per hour2.12.2 Conversion of the overload capability to lower overcurrentsThe stated cycle can be converted for lower overcurrents, but not for higher!The following formula is used to calculate the new time:T xnew = New permissible time for the new overcurrent XnewX new = Required overcurrent (must be less than the stated values)ExampleFor X = 3, Tx = 5 s: With a reduced overcurrent (X = 2.5) a new permissibleovercurrent duration Txnew of 7.2 seconds is calculated.￫ The appendix (￫ page 219) contains overload curves for varioustime, current, and starts-per-hour combinations that can be usedto select the right DS7 soft starter for your application.Overcurrent X [x] Overcurrent time Tx[s]Duty factor F [%] Starts per hour SDS7-34… 3 5 75 10Txnew = X2 x TxX2newTxnew = 3 2 x 5 s = 7.2 s2.52￫ The parameters X x Ie, T and the number of starts allow anynumber of combinations of this load cycle with the samethermal load.
