When you plan a UPS installation it is always important to consider bypassing arrangements. You cannot avoid maintenance on a UPS system. No matter how efficient the system or well designed it is in terms of a maintenance access and a modular UPS design, there will come a time when the system has to be powered down and removed from circuit. Without a UPS maintenance bypass switch this also means that the load also has to be powered down.
Your chosen UPS system may have an internal maintenance bypass switch. This may be sufficient for your maintenance purposes and should prevent the UPS system exposing the UPS maintenance engineer to live voltages. However, the system is still live and only partially isolated. In addition an internal bypass arrangement does not allow the UPS to be powered down and removed from circuit.
An external UPS maintenance bypass switch sits in line with the electrical cable installation between the distribution board from which the UPS system draws its mains (or generator) power and the output distribution arrangements. Above 3kVA all connections are hardwired for electrical safety reasons and to meet the electrical regulations. Below 3kVA they may be hardwired or plug and play using IEC-type cable connectors with or without locking clamps such a mechanism
On the output of the UPS, your installation may run from a further distribution board to which are connected your critical loads either directly or via a power distribution unit (PDU) arrangement. In the electrical installation, the UPS bypass switch is often installed ahead of the uninterruptible power supply delivery. The bypass switch is a part of the electrical switchgear arrangements and electrical installation. UPS bypass switches have two further connections, for the UPS input and output cables.
UPS bypass switches may use a manually turned rotary switch or circuit breakers for the switching arrangement. It is important to check that the switching mechanism is a make-before-break type as opposed to the break-before-make type. The latter would expose the critical load to short breaks in supply as the switching between UPS output and mains power (and the return) occurs.
It is also important to ensure that the UPS maintenance bypass switch is manufacturer certified as the switching arrangements can affect UPS operation by placing a short on the UPS output and/or activate an alarm code. Some UPS manufacturers require the fitting of a communications cable between their uninterruptible power supplies and the external maintenance bypass switch to avoid alarm activation and ensure the UPS can report on the correct state of its bypass arrangement. Such signaling arrangements are often overlooked and yet the provision for signal contacts (normally volt-free) should be built-into your UPS maintenance bypass for remote monitoring via a Building Management System (BMS). You may even consider adding a local GSM modem for external maintenance bypass status reporting.
Castell interlocking arrangements may also be important and even more so in parallel bypass configurations. Castell is a form of key locking that prevents bypass operation without it being in synchronisation with the UPS and mains power supply. Castell bypass arrangements add cost to the electrical bypass arrangements but provide a further level of security.
In a parallel uninterruptible power supply configuration, each UPS system can be installed with its own external UPS maintenance bypass or a single wrap-around one for the entire system. The latter will have to be sized for the entire parallel UPS system output and will therefore be most costly to purchase and install (due to the larger Amperage and cabling requirements).
At EcoPowerSupplies we install and supply our own range of UPS bypass switches. These are manufactured within our group and installed by our own NICEIC certified electrical contracting team. As a UPS maintenance bypass switch manufacturer we are able to provide custom and bespoke bypass switch designs and have an extended bypass range suitable for datacentre, rail transportation and industrial applications.