Trust chief executive Liz Davenport said the move was “due to a rise in the numbers of people both in our communities and in our hospitals with Covid-19”.
She said: “We are keeping our policy under constant review and will make further adjustments as needed.”
The move comes as public health bosses said that one in every 35 people in Devon – 2.87% – currently had coronavirus.
Steve Brown, director of Public Health Devon, said the new figure was from “the latest data from Tuesday evening” after figures earlier this week said one in 45 people had it.
He said the data showed “how things change on a regular basis”.
He also reiterated a message for people to stay home if unwell.
He told BBC Radio Devon: “While there’s no legal requirement to isolate … if you feel unwell, and if you can stay home, do stay at home because that is the best way to try and reduce the risk of giving it to others.”