Question about margin calls...

So..this is probably a basic question:

In my account I have an "Exposure coverage" and "Margin utilisation". The exposure coverage is for example: 10% - but the margin utilization is 20%. So my question is:
When should I expect a margin call? When the exposure coverage reaches 100% or when the margin utilization reaches 100%? thanks...

I've not seen the "exposure coverage" term, but my guess is when the exposure coverage hits 100%, but brokers vary in how they handle initial vs. maintenance margin. You should check your broker's specifics.