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Chapter 12 Helpful information
If any of the affected UPS units get damaged and repair is required, the repair work is not
covered by warranty or an existing maintenance agreement / service contract.
Reasons why UPS daisy chaining may be considered
Redundancy
Added redundancy or reliability is a good target especially when considering a single UPS can
be a single point of failure. A mathematically-based probability study shows that placing UPS
units in cascade then this increases the chance of failure, as failure rates are combined to
present the new failure rate. A more practical way of thinking about it is, if the UPS closest to
the load fails or has a catastrophic failure then the remaining UPS provides no value even if it is
still operating.
Runtime
Batteries are stored energy and the bigger and larger the battery bank, the more runtime is
provided. But for customers looking for more runtime from an existing UPS, there are no
shortcuts. Plugging a UPS into another UPS is very likely to prevent one or both of the UPSs
from working correctly due to inverter compatibility issues. In this type of scenario, the UPS
closest to the load doesn't recognize the first UPS unit power as sufficient and both UPSs go to
battery, defeating the intent.
The run time of a UPS can be extended by adding extended battery modules (EBMs) to the
UPS unit.
Surge Protection
Every UPS should have an adequate level of surge protection for most applications. But some
customers may be in difficult environments where thunderstorms are frequent or industrial
equipment within their building wreaks havoc on their electrical system. In either case,
cascading UPS units does not help mitigate, or clamp, incoming surges. In fact, cascading the
UPS units could create some new challenges to the system. Note that the UPS is designed to
be self-sacrificing in regards to surges. That means if the surge is too much for the first UPS,
that UPS will take itself offline and the system will go down regardless.
For sites with known issues, it is best to consult with a qualified and licensed electrician to
develop a multi-stage approach. Surge protection at the UPS is best when paired with surge
protection at the panel board and customers worried about lighting should explore if lightning
arrestor solutions are appropriate.
6U Rack or Tower UPS RT8kVA and RT11kVA IUOMG
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