Walmart will cut health-insurance coverage for employees who work fewer than 30 hours a week. Starting Jan. 1, these 30,000 part-time workers will be left without health benefits. The move by the nation’s largest private employer follows similar cuts made by Home Depot and Target to curtail the rising costs of paying for insurance. “We have to make some decisions,” said Sally Wellborn, Walmart’s senior vice president of benefits. Walmart, which has 1.4 million full- and part-time employees, previously announced that 1.2 million workers and their families are enrolled in their health-care plan. The amount far exceeded what the company expected. Walmart will also be raising premiums for all of its full-time workers.