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Chapter 12 Helpful information
RCCBs in IT environments
Residual current circuit breakers (RCCB), also known as Residual Current Device (RCD), Earth
Leakage Circuit Breaker (ELCB), Differential (Lock) Circuit Breaker, or GFCI (Ground Fault
Circuit Interrupter device).
In many areas residual current circuit breakers (RCCB) are mandatory to be used as defined by
local law, standards or technical connection terms and conditions as provided by the utility
power company. From a technical perspective, it RCCBs primarily serve as a protection from
indirect contact with utility power and in certain situation as fire protection.
The use of RCCBs in modern IT environments is to be viewed critically.
RCCB
In simple terms, an RCCB monitors the sum of the currents flowing into and out one protected
part of the electrical network simultaneously at the same time. This is only done on the active
lines, that is L1, L2, L3 and N. The residual current (delta current) in this measurement is
limited by the threshold of the residual current circuit breaker. In case this threshold is
exceeded the RCCB opens all connections on all active lines of the monitored / protected area.
In short the power on all lines will be cut.
The current that flows via the protective conductor (PE) is not monitored by the RCCB and
therefore is not included in the vector sum! If as a result of the design of power supplies for
example the filter leakage currents are discharged against PE then the result will be fault
currents, that is residual currents. These are recognised by the RCCB. Due to the number and
type of devices in IT environments substantial residual current flow can occur which leads to a
quick triggering of the RCCB. This will inevitably lead to a complete shutdown of the
monitored IT environment, leading to a total failure of the said IT environment not considering
the fact that there may actually not be a technical fault present nor the likelihood is given of
direct utility power contact by a user!
The same shutdown will happen when a user must test the RCCB in regular intervals by
pressing the test button as compulsory set out by the RCCB manufacturer.
Furthermore, it has been observed that often problems arise with UPS systems, provided that
these are protected by means of RCCBs. Please refer to the documentation provided by the
UPS manufacturer.
All the above also applies to the in recent years more popular becoming RCBOs, that is
Residual current operated Circuit-Breaker with over-current protection, which are also known
as GFCI (ground fault circuit interrupter).
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6U Rack or Tower UPS RT8kVA and RT11kVA IUOMG
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