The four seats are Dhanbad, Dumka, Rajmahal and Godda. The Bharatiya Janata Party (BJP) won three of the four seats in 2009, while the JMM had won the Dumka seat.
An electorate of over 61 lakh will decide the fate of 72 candidates.
Polling will take place at 7,489 polling stations, of which 2,439 have been categorized as sensitive and 1,154 as highly sensitive.
Officials said 37,445 people have been pressed into poll service.
In the third phase, 415 booths have been declared model polling stations. Also, 400 polling stations will be connected through webcasting, 1,015 through video and 1,954 will have still cameras, an official said.
Around 45,000 security personnel, including CRPF, Jharkhand Jaguar, Indian Reserve Battalion, state police and home guards, have been deployed.
In the third phase, all eyes are on Dumka where former chief minister and president of Jharkhand Vikas Morcha-Prajatantrik (JVM-P) Babulal Marandi and another former chief minister and Jharkhand Mukti Morcha (JMM) chief Shibu Soren are locked in a fight.
Both leaders have a large following in the tribal community.
Coal city Dhanbad is witnessing a fight among incumbent BJP MP P.N. Singh, Congress’ Ajay Dubey and the TMC’s Chandra Shekhar Dubey.
Godda is witnessing a triangular fight between sitting BJP MP Nishikant Dubey, Congress’ Furkan Ansari and JVM-P legislator Pradeep Yadav. The fourth key candidate is former IPS official Subodh Prasad who is fighting on the All Jharkhand Student Union (AJSU) ticket.
In Rajmahal, the BJP has fielded Hemlal Murmu who was a JMM legislator and quit membership of the assembly just before the polls, while the JMM has fielded Vijay Hansda who joined the party just before the election.