At Tuesday’s annual town election, voters will be asked to pass a temporary property tax increase, through a Proposition 2 1/2 debt-exclusion override, to fund the town’s share of a $40 million expansion and renovation project at Central Elementary School. If the funding is approved, the town would borrow about $19 million to complete the work. Plans call for the revamped school to house the town’s middle school students, in grades 5 to 8, with its younger students shifted to the other elementary schools in the district. If voters endorse the project, work would begin this summer and be completed by the fall of 2014.Polls will be open from 7 a.m. to 8 p.m. Voters also will decide three contested races. Four candidates are competing for two seats on the Board of Selectmen, with incumbents R. Paul Rotondi and Robert W. Sweeney running for reelection against Thomas H. Boussy and Anthony C. Kennedy. Five candidates are running for three constable positions: Robert E. Moreira and Robert W. Nardone are running for reelection against Brian M. Johnston, David B. Luciano, and Edward P. Westhaver. Five candidates are seeking to fill the town clerk vacancy: Kevin C. McLaughlin, Paul E. Means, Michael J. Ronondi, Maria Sagarino, and Mary R. Cerasuolo Zatta.