The invention provides a relay unit and a control method for the relay unit. The reliability of testing a normally closed contact in a relay unit may involve the following. While the load is de-energized, sending a test signal to a normally closed contact (b1, b2) and detecting the state of the returning test signal sent. Resending a test signal when a detection result does not satisfy a predetermined criteria, and re-detecting the state of the returning test signal resent. The state of the returning test signal resent may be assessed as normal when the re-detection result satisfies the predetermined criteria.