Change of Stock Series from EQ to BE

I know that the Intraday trading is not allowed in the BE series.
Can anyone tell on what basis the exchanges change the series of the stocks, like from EQ to BE series?
And what is the reason for changing the series from BE to EQ and vice versa?

NSE reviews stocks moving to on a fortnightly basis and stock moving to and from T2tT on a quarterly basis.

Fortnightly criteria

  1. Price Earnings Multiple (P/E) less than 0 or greater than or equal to upper limit # subject to a minimum of 25 as on the relevant date.
    (# If Nifty P/E on the relevant date is in the range of 15-20, then the upper limit will be 30. If Nifty P/E >20 or <15 then the difference rounded off to nearest number will be added to or subtracted from 30). AND

  2. Fortnightly Price Variation is greater than or equal to Sectoral Index* or Nifty 500 Index Fortnightly Variation plus 25% subject to a minimum of 10%
    (*In case a particular Sectoral Index is available only on one exchange the other exchange shall also use the same to compare price variation in securities of the concerned sector for the purpose of shifting to Trade for Trade segment). AND

  3. Market Capitalisation of less than equal to Rs. 500 crores as on relevant date.

The quarterly critetia is explained in details here

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