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Description of Galvanic Isolation

Galvanic isolation in power equipment refers to the fact that the output power circuit is electrically and physically isolated from the input power circuit. Electrical isolation is accomplished using an isolation transformer. Physical isolation means that the output power wiring does not touch or connect to the input wiring.

All personal computers already have galvanic isolation between the input power and the computer logic built in. This is a requirement of international safety agencies in order to prevent shock hazard. Therefore, the addition of another transformer is redundant.

Many people mistakenly believe that galvanic isolation corrects noise on ground (earth) wiring. This is not correct. In fact, all galvanic isolation transformers only isolate the power wires, but pass the ground wire straight through.

Some UPS systems provide galvanic isolation. Most on-line UPS units do not provide galvanic isolation, despite the widespread misconception that they do. For example, Exide, Unison, and ON-LINE (Pheonixtec) on-line models do not provide galvanic isolation. The standby ON series by Oneac does provide galvanic isolation. Therefore, isolation is not a function of the type of UPS, but rather a feature that can be added to any UPS.

The actual benefit of installing an isolation transformer is that common mode noise fed to the computer is greatly reduced. Common mode noise can also be reduced by using noise filters, such as in the APC Smart-UPS series. The filters can work as well as the isolation transformer, especially at high frequencies where computers and networks operate. The isolation transformer is better at very low (audio) frequencies.

Computers and computer peripheral equipment are not affected by audio frequency noise on the power line. Therefore there is no benefit of the isolation transformer over filters for computer applications. The disadvantage of the isolation transformer is the extra heat which shortens UPS battery life if the batteries are in close proximity. Another disadvantage is that the UPS weight dramatically increases with an isolation transformer.

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