Cable Sequence Issue
During the first of three annual TEGG visits it was noted that the identification of the incoming and outgoing cables of a UPS module were out of sequence. We suspected that during installation the phase conductors had been connected incorrectly. This in itself did not affect the daily function or efficiency of the system and the module would have continued to function normally. The main concern was personnel safety as the UPS system fed computer equipment the trading desks as well as I.T. servers in the data centre.
As each trading desk had UPS power outlets and outlets that were supplied from the normal distribution system the concern was that a voltage above 230V would be present at the desks if the two outlets were served by different phases. Unfortunately there were no record drawings or labeling to identify which system supplied each of outlets.
As safety was the prime concern we immediately alerted the site maintenance staff who were able to notify the office staff that nothing should be plugged into or removed from the desk outlets until a full survey had been carried out and the circuits had been identified.
To confirm our suspicions we carried out phase rotation tests at the incoming and outgoing connections at the UPS module and at the incoming supply from the site transformer. The outgoing phases were reversed.
As the site was so remote and our time on site was limited the site staff carried out a full survey of all desk power to confirm if the phase reversal had resulted in two phases being present at the desks. Equipment was unplugged and all circuits were identified.
Fortunately none of the desks fed by the UPS system were found to be supplied form different phases. Although the surveys did involve small shutdowns of the desktop power circuits, these were carried out during evenings and weekends so had no affect on the trading activities.
The surveys allowed all the UPS and Essential circuits and distribution boards to be correctly identified and tested. Circuit charts and record drawings were also updated and produced making future faultfinding and testing much less time consuming and ensuring user safety.