B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 365; Flight Crew Type 10000
Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Human Factors
While on downwind for an approach to OAK Runway 30; ATC gave a turn to base and a descent from 4000 ft to what I thought was 2400 ft. I thought the FO read back 2400 ft; and as I was hand flying I asked him to set 2400 ft in the altitude window. Descending through 2900 ft MSL ATC advised us we were below our assigned altitude of 3400 ft.  I immediately climbed the aircraft to 3400 ft and remarked to the FO that I thought we were cleared to 2400 ft. ATC then said we were below the minimum vectoring altitude for the sector.  Published altitudes on the ILS 30 Approach are 2700 ft for WUVON and 2000 ft for MITOE (FAF). As we were being vectored to intercept final near WUVON; the 2400 ft altitude didn't seem unreasonable. At no time did we receive a GPWS warning. Both Pilots had TERRAIN selected on their map displays; and no terrain conflicts were noted.
[Report narrative contained no additional information.]
B737 flight crew reported a low altitude alert on approach to OAK due to miscommunication on the cleared altitude.