Source Transfer Switches
Source Transfer Switches (STS) or Static Transfer Switches is another name they have been called, are used to increase the resilience of power continuity plans by introducing a dual-input source of primary AC power. An STS device will automatically connect its output to one of two AC power sources known as primary and secondary supplies should the the preferred source go out of tolerance. These can include: two uninterruptible power supplies, or two mains power supplies, or a combination of the two. STS devices can also be ‘switched’ manually and remotely. Small STS systems generaly rated at 16Amp tend to be relay-based with fast switching characteristics and are relatively cheaper then synchronous STS designs. However, Synchronous STS design offer additional security when protecting loads of 32amps or more. STS solutions generally incorporate Power Distribution Units (PDUs) with up to ten output IEC 320 type sockets, with intelligent monitoring including voltage and load percentages. Larger STS systems tends to be hardwired and used within more complex switching arrangements of a power continuity plan.
Most static or source transfer switches whether single or three phase can be used as generic devices within a UPS installation. Manufacturer specific static or source transfer switches may be preferred for site-wide monitoring and control using manufacturer specific remote monitoring software packages.
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