Residual Current Device https://www.electrical-installation.org/enwiki/Types_of_RCDs There are 4 types of RCDs - Type AC - Just protect against AC supplies. No longer available, should be replaced. - Type A - Type B - for machines with VFDs. 3 phase - Type F - for machines with VFDs. 1 phase Type B and F provide protection against more types of electrical current (DC, pulses, different frequencies). They also are designed to be able to avoid a lot of the nuisance trips associated with machines that have a lot of drives. All sockets for final subcircuits with a rating not exceeding 32A need to have RCD protection [AS3000:2.6.3.2.3.3] ## UPSs The RCD requirements for UPSs is not clear. Some items of note are - An RCD on the input side of a UPS will not provide protection at the load socket (because the UPS battery will continue to provide power after the RCD trips) - An input RCD will protect against an earth fault inside a UPS (and is required for any circuits with a socket as well as hardwired UPSs that are fed from anything less than a 32A CB) - UPSs have outlet sockets that are not RCD protected. Not sure why this is legal. - You can get PDUs with in built RCDs - For Transformer isolated UPSs an RCD on the output would not work and would not provide any protection [APC Site issues with Earth Leakage](https://www.apc.com/au/en/faqs/FA156793/) [Whirlpool Discussion](https://forums.whirlpool.net.au/archive/2682297) Someone asked about RCDs in server rooms. Answers are mostly terrible. ## Relevant sections of Australian Standards - AS3000:2.6.3.2.3.3 Requirements for additional protection