Yes, you need a 20A circuit to take full advantage of BIT20. In my case, I was thinking of getting a BIT20 to run my desktop 15A circuit for a bit of time and then to move the BIT20 to a dedicated 20A circuit later on in the main room. I wanted to know if it was safe to use the BIT20 temporarily on a 15A circuit. I ended up with a BIT15 for the 15A circuit.