Intel XEON E7-4830V2 is not supported on both PowerEdge R420 & R520. Below is the family of processor supported in these platforms. You can refer links provided for more details One or two Intel Xeon processor E5-2400 and E5-2400 v2 product family [URL] [URL]
Hello,  i would like to know if i can get a list of CPU's that work with Dell PowerEdge R420 & R520 Servers and if the  CPU's Intel XEON E7-4830V2 - SR1GU or Intel XEON E7-4830V3 - SR222 would work on them ?   Thank you in advanced to everyone how replies 
Dell PowerEdge R420 & R520 Processor Compatibility