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Chapter 12 Helpful information
Most Common Problems
When a customer calls with a problem with a tripping RCD, one should never assume that the
UPS unit is faulty without doing the required troubleshooting.
1. The EN50091 permits a leakage of up to 3.5 mA per pluggable appliance. If there are
10 appliances connected with an average 3 mA per appliance, the RCD can still be
tripping even without a faulty appliance. In this case try and ascertain if it still trips
when the UPS is connected on it's own, if possible on a dedicated RCD.
If this is the case, the UPS chassis requires replacement, if not, then the electrical
installation and other appliances have to be checked.
2. There are also issues when power electronics are connected. Some SMPS loads cause
high leakage after being switched on. In such cases it is recommend that a selective
type of RCD is used. These RCD's have a slight delay, which allows them to overcome
this relative short period of earth leakage.
3. In a new electrical installation RCD's may trip due to an error in the wiring, such as
neutral wires being mixed up at distribution board.
Tripping Currents
The most common tripping current for an RCD is 30 mA but there are also types with a
tripping of 10 mA and 100 mA tripping current to offer shock protection.
There is also a 300 mA and 500 mA, which gives overall protection against risk of fire from
electrical faults in wiring etc. These are usually used at the main distribution board in a TT
network, where the main fuse may not react fast enough in the event of a short circuit to earth.
6U Rack or Tower UPS RT8kVA and RT11kVA IUOMG
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