An air carrier Captain crossed the runway hold short line; resulting in ATC sending an aircraft around.

Narrative

The taxi out from the gate to Runway 30R was short and I should have advised the flight attendant that it would be so. I did taxi slowly and I thought that she should have had enough time to complete her before takeoff announcements. While taxing to the runway we were cleared into position and hold before the before takeoff checklist was completed. As I approached the runway; my First Officer advised the Tower that we needed 10 more seconds. Tower told us to hold short; but I was unable to stop the aircraft before about 5 feet of the nose was past the hold short line. Tower called to have us read back the hold short instructions; which I did as the First Officer was now asking the Flight Attendant if she was ready for takeoff. She said that she was and that she thought that she had chimed us. During this time; I was talking to Tower to tell them that we were in fact beyond the hold short line. Tower then told the inbound flight to go around. The First Officer then advised me that the Flight Attendant was ready for takeoff. We were then cleared into position and hold. Tower then cleared us for takeoff and the flight proceeded without incident. I was concentrating on the Tower's instructions and taxiing the aircraft. There was no rush; we only had one leg that day and we were not late.