very simple job. You need a 30mA RCD (the most common type) rated to carry a current equal to or greater than the fusing of the circuit (they are usually rated at 80A or 100A so almost any will do).
(there are also available 100mA RCDs, and time delayed RCDs. These are more expensive, less common, and not what you need)
Once the RCD is fitted, it will start to trip if there is any earth leakage on the garage circuits. if this happens you will need investigation and rectification of the faults and may lead you consider having it rewired.
(there are also available 100mA RCDs, and time delayed RCDs. These are more expensive, less common, and not what you need)
Once the RCD is fitted, it will start to trip if there is any earth leakage on the garage circuits. if this happens you will need investigation and rectification of the faults and may lead you consider having it rewired.