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7/21/2011 11:50 AM | |
Posts: 66 Rating: (4)
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Dear Paolo, For switching devices connected downstream to a protective device (fuse or circuit breaker) you normally have to know the permissible let-through current (Id) and let-through energy (I^2t-value). These are properties ofthe device and have to be provided by the supplier. These values have to be higher than the values you can take from the let-through characteristics (Id and I^2t) of the upstream device for the prospective short-circuit current. So for your application first check the catalog for the permissible Id and I^2t of the 3KA55 (LV 10.1 chapter 7, available on https://www.automation.siemens.com/mcms/infocenter/content/en/Pages/order_form.aspx?nodeKey=key_9177913) and then check the let-through characteristics of the 3VL (http://support.automation.siemens.com/WW/view/en/20370652/134300) for Id and I^2t at the prospective short-circuit current. On the other hand, when your calculation in SIMARISdesign is without error messages dimensioning is all right - SIMARIS incorporates these values for the included devices. 3KA55 is OK for your application. Best regards Sentronix
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