Hi,
At present nifty lot is of 50. margin at order is nearly 20000, If you place order ATM. But you receive premium also. Suppose Nifty is at 3650 and you place put at 3650. Suppose at 3650, put is at Rs130. You need to give margin amount of 20000 and you will receive premium of 130*50 = 6500Rs.
If Nifty goes against you you need to increase margin to avoid unexpected trigger by your broker.
Above information I found from ICICI. This may differ from broker to broker.
Experts please let me know if my understanding is wrong.
Manish