Cuto marks for SC category vary every year. In 2017 the cutoff marks is 32, in 2016(50), in 2015(52). So its vary every year according to the Difficulty level of exam and the students score. But you can't get any NIT by just clearing cutoff. Cutoff is just an eligibility criteria for jee advance. If you want to get into any NIT than you should score 90+.With 90+ marks you will only got seat at NIT. But if you want CSE branch than you should score 140+. If you want CSE at top NIT than you should score 190+. Above marks can vary every year.

Cuto marks for SC category vary every year. In 2017 the cutoff marks is 32, in 2016(50), in 2015(52). So its vary every year according to the Difficulty level of exam and the students score. But you can't get any NIT by just clearing cutoff. Cutoff is just an eligibility criteria for jee advance. If you want to get into any NIT than you should score 90+.With 90+ marks you will only got seat at NIT. But if you want CSE branch than you should score 140+. If you want CSE at top NIT than you should score 190+. Above marks can vary every year.

The cutoff marks in jee mains for  "SC" candidate is around 60+ to qualify. 

Here is the link for opening rank and closing rank of various institutes : https://josaa.nic.in/result/result/openingclosingrank.aspx