Power supply manufacturer PULS UK is urging companies to look closely at the redundancy back-up systems providing emergency power to mission-critical production equipment. PULS believes that many supposedly fail-safe systems are not as secure as operators think.
Common problems affecting redundancy systems include batteries in DC UPS and AC UPS units not functioning correctly – either because their useful life has expired or they are working outside their temperature range; AC UPS or generators that are not sufficiently powerful for the inrush current needed for the system; offline AC UPS systems that appear to be functional but are not; and single fusing of the input circuits of redundant power units. PULS’s engineers have even seen systems where various components have not been connected or have been wired incorrectly.
"It is on the AC side that we see most mistakes being made, especially when it comes to the correct installation of fuses," said PULS UK’s Managing Director Harry Moore. "A typical example happened last year. Two 20-amp power supplies wired in parallel were being used in a redundant system requiring 20 amps. Although the company had fused each of them separately they had been wired through a single breaker at the junction box. The junction box fuse was higher rated, but the length of the cabling and the power available at the individual power supply fuses meant that the single breaker tripped first, resulting in the redundancy system being rendered useless."
In this case the problem was soon rectified, but the disruption to production caused by the unnecessary failure proved very expensive.
Production equipment is usually very reliable and in some respects this is part of the reason redundancy systems are neglected. It’s only when something goes wrong and production grinds to a halt that a fault or design error is found.
Harry Moore continued, "I would urge operators to look carefully at their redundancy systems to make sure everything is working correctly. Most production equipment is very reliable, but if the worst happens and the redundancy system is not up to the job, the result can be very expensive."