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Chapter 12 Helpful information
Daisy chaining / cascading UPS units
What is daisy chaining / cascading UPS units
Daisy chaining or cascading of two UPS units is when the input power connector of a
downstream – also called slave or secondary – UPS unit is connected to the output power
connector of an upstream – also master or primary – UPS unit.
In this section the term "cascading" instead of "daisy chaining" is used.
E xample:
The C20 input connector of a 3 kVA UPS unit, 5594-3KX (RT3kVA 2U Rack or Tower UPS,
200-240VAC), is connected to a C19 output connector of a 5 kVA UPS unit, 5594-5KX
(RT5kVA 3U Rack or Tower UPS, 200-240VAC).
Symptoms
Either the upstream / master UPS unit or the downstream / slave UPS unit or both may be
operating incorrectly or appear to be faulty.
Additional information
In such a setup, the master UPS unit is also referred to as primary or upstream UPS unit whilst
the slave UPS unit is referred to as secondary or downstream UPS unit.
When cascading UPS units, UPS controllers will work against each other and this will cause
harmonic distortions on power lines.
Under no circumstances should one (1) UPS unit input be attached directly or indirectly to the
output of another UPS unit as the current draw of the second UPS unit may cause a distortion
of the output voltage waveform of the first UPS unit, which could cause the second UPS unit to
detect this as a power fluctuation resulting in it going onto battery power and continually
cycling between battery and normal operation.
The current draw of the second UPS unit when charging the batteries could also cause the
upstream UPS unit to go into an overload condition. The results of feeding one (1) UPS unit
from the output of another could have other more disastrous results.
The size and type of the upstream UPS unit does not matter as any UPS unit can be caused to
fail in such an installation.
By cascading UPS units, another point of failure will be introduced into a system that is already
backed up by a UPS unit.
If issues arise, no assistance can be given for such a setup.
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6U Rack or Tower UPS RT8kVA and RT11kVA IUOMG
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