The emerging field of private health-insurance exchanges through which companies can provide employee health benefits grew by one potentially significant player on Thursday.

Extend Health, which consulting firm Towers Watson purchased in 2012 and is the largest competitor in a crowded field of exchanges for Medicare-eligible retirees, is expanding into the active-employee market under the new name OneExchange.

OneExchange has a ready roster of potential customers for the active-employee exchange. The exchange can be made available to both full-time and part-time workers. More than 250 employers, including 45 Fortune 500 companies, already offer Extend Health to their retirees, Towers Watson says.

In addition to selecting a purely private exchange, corporate customers will be able to choose an option for companies where some employees will benefit by buying insurance through one of the public exchanges being created under the Affordable Care Act (ACA).

Part-time workers, seasonal employees, and early retirees who do not qualify for the group plan can also access public exchanges and, like all OneExchange users, receive support and guidance from OneExchange benefit advisers.

Benefits experts have predicted that more private-exchange options for active employees will appear as 2014, the year when numerous changes mandated by the ACA are scheduled to take effect, draws near. Until now, there have been only a handful of such options.

Additional OneExchange solutions will be triggered as final regulations for ACA provisions are finalized, Towers Watson says.