The thirty year-old defender has joined on a short term loan deal until back-end of February as Malky Mackay boosts the strength of his defence.
"As soon as we found out Liam was a possibility, we moved quickly," manager Malky Mackay told the club's official website.
"We have him until the start of the MLS season in mid-February and hopefully we can make good use of his experience in that time."
Ridgewell is expected to come in at left back with Andrew Taylor dropping to the bench.