Category ‘B’ SPADs (Signals Passed At Danger) are the result of drivers passing signals when no aspect is showing. A national 650V UPS project was started to ensure that signal lamps and points remain operational should the power supply be interrupted. Thirteen sites situated were identified across the country where there have been problems maintaining a continuous power supply to signals or where a SPAD could cause major problems. Each signal installation has a 650V supply provided from the local electricity company through a step up transformer with a standby generator, which starts should the power fail for longer than a few seconds. During normal operation, the UPS was designed to protect the signalling system from transient power disturbances such as spikes, sur

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