In an ECB occasional paper, Ulrich Bindseil, Marco Corsi, Benjamin Sahel, and Ad Visser review the European Central Banks’s collateral framework.
From the executive summary, on misconceptions:
… differences e.g. with interbank repo markets: first, central banks are not subject to liquidity risk in the way “normal” market participants are, and can therefore accept less liquid collateral. Second, as the central bank has a zero default probability in its domestic market operations, collateral providers are willing to accept severe haircuts to obtain credit. …
According to the authors the ECB is the most transparent central bank when it comes to its collateral framework. But the latter is also complicated:
However, it is true that the ESCF is relatively broad in terms of the scope of eligible collateral and rather complicated. This is inevitable because of the diversity of financial institutions and markets in the euro area.