What are the criteria for shifting securities from normal to trade to trade (T2T) series?

A lot of the times, I see that stocks trading in the normal segment are shifted to T2T with no prior notification. When stocks move to T2T I can’t trade intraday or BTST, which is quite painful. Is this arbitrary or is there a way to know which scrip will be moved and why?

Quoting from this NSE circular,

Currently, the surveillance action whereby securities are transferred for trading and settlement on a trade-to-trade basis is reviewed monthly. These criteria for shifting securities to/from Trade for Trade segment are decided jointly by the stock exchanges in consultation with SEBI and reviewed periodically.

So, we can safely say that these series shifts aren't arbitrary. (NSE shifts securities from the EQ series to BE or BT, both of which are T2T).

There are certain criteria (mentioned in the NSE circular linked above and this BSE circular) which I won't go into details about. Essentially, the exchanges look at the PE ratio, volatility and price movements for the scrip and decide whether it needs to be moved to the T2T segment. Market capitalization is also taken into account. If the market capital of a company is less than INR 500 Cr, then it is liable to be shifted to the T2T segment (exemptions to this rule also mentioned in the linked circulars).