Backup Power is also known as an Emergency Power System, Backup Power Systems are types of systems that may include generators, lighting and many other apparatus, to provide a backup of resources (power) incase regular power systems fail or incase of a crisis. Backup Power is by many different people / companies / industries around the world, these include: Residential Homes, Data Centre, Modern Naval ships, Scientific Laboratories, Telecommunications Equipment and one of the most important places where Backup Power is needed is in Hospitals. Hospitals greatly rely on the knowledge that should anything happen to their power system they have Backup Power in place. A hospital could not run efficiently with out it, if there was to be a power failure every single piece of medical equipment in a hospital would shut down. This could be minor things like computers or monitoring equipment… but in some cases this could be dangerous, if a patient was on a Life Support Machine that machine would fail rendering it useless and putting the patients life at risk. Every Hospital should have its own form of backup power, usually backup generators and large hospitals may even have multiple of these incase the unlikely incident of a backup Power system also failing.

Backup Power systems can date back to as early as World War II, they were used on Naval ships. These Naval Ships were at danger of loosing the function of their steam engines during combat, the steam engines powered the steam driven turbines for the generator. In this case they used one or often more than one diesel engines to drive back up the generators. Early transfer switches were not automatic tho and they relied on manual operation. There would be two switches that would be placed horizontally, in line and the on position of the switch would be facing each other. A rod was placed in between the two switches and in order for the switch to function one source must be turned off, when switched off this moves the rod to the other side where the other source is turned on.

To avoid a long supply of electric wires a central battery system with automatic controls is used, this is located in the power station building itself. This type of system is used for a 208 VAC Backup Power Systems. The central battery system of the Backup Power consists of lead-acid battery cell units, these make up a 24 or 12 VDC System, stand-by cells are also used each with its own battery charging unit. Voltage sensing units are also required and they must be capable of receiving 208 VAC. Incase the 208 VAV station supply fails an automatic systems is required, this automatic system must be able to signal and activate the emergency supply unit.

Nuclear Plants also require a for of Backup Power, however this is slightly different and is know as EDG's (Emergency Diesel Generators).