1. Applicable Locations

In certain situations, particularly for safety reasons, isolation transformers are necessary. For example, some household appliances have live chassis, which can pose an electric shock hazard during maintenance. Suppose an isolation transformer is used as the power source for repairs. In that case, the technician can safely touch the appliance's chassis without worrying about electric shock (as long as they do not simultaneously touch both live wires). This is more advantageous than installing an RCD (Residual Current Device) at the power source. Although an RCD will trip in the event of an electric shock, the person might still feel the discomfort of an electric shock. With an isolation transformer, however, there is no sensation of electric shock when the body comes into contact with a live component, making it the preferred choice for appliance repair professionals. Additionally, isolation transformers are needed when converting a TN grounding system to a local IT grounding system. According to regulations, different grounding systems should not coexist within the same power supply system. If another grounding system is required, an isolation transformer must be used for the conversion. For instance, in hospitals, the IT grounding system used in operating rooms is typically created by converting the hospital's TN grounding system using an isolation transformer.

2. Requirements for Using Isolation Transformers

When using an isolation transformer, the secondary side must not be connected to a PE (Protective Earth) line. Connecting to a PE line would negate the isolation effect. Additionally, this prevents the risk of electric shock due to fault voltage being introduced via the PE line, which is a drawback of TN grounding systems. Furthermore, one isolation transformer is recommended to supply power to only one electrical device. If multiple devices need to be powered, it is preferable to use an isolation transformer with multiple secondary windings. When conditions do not permit this, and a single secondary winding of an isolation transformer must power two devices, the metal enclosures of both devices should be connected using an insulated wire, and this wire must not be grounded. This method, known as ungrounded equipotential bonding, helps eliminate the risk of electric shock caused by "shell-to-shell" contact between devices connected to different phases of the power supply.