Hello,
According to your mentioned rank your son's general category rank will be around  13K. with this rank he will get electrical at the new NITs, however with domicile he might get mechanical at the top NITs.
You can use the college predictor tool available on our website to predict which colleges you can get, link :https://engineering.careers360.com/jee-main-college-predictor?utm_source=C360&utm_medium=qna&utm_campaign=jee-main-college-predictor
all the best :)