Quote from NickBarings:
That's what we have margin requirements for
It's just 2% to initate a position. Excess liquidity can go negative.
So imagine a trader uses his full account equity to take an aggregate 5m or more position and one or more goes radically against him.
Or if he/she use his entire account equity, the positions initially go in his favor and he/she uses his excess liquity to initiate more positions. Then one or more positions go radically against him? Where are the funds going to come from to bring his excess liquidity positive?
IB.
They close out all positions and end up having to pay the banks the negative difference.
You don't have the problem with the CME because, one, there is centralized clearing and two, the have a maintenance minimum at which positions are flagged and either liquidated or the customer asked to put up additional margin to bring the position back above maintenance. But in forex, there's no such thing. What is more, you can contrive all sorts of exotic positions.
Ask yourself, why do most ECNs have a margin rate 50:1 or less but most bucket shops have a margin rate of 100:1 to as much as 400:1?