User Manual 10H52258UM60 - Rev. 3 - 01/2019
24
APM 400/600
Electrical Installation & Connections
4.1.8
External Protection Devices
In order to guarantee safety, external circuit breakers should be installed on the UPS input and battery lines.
Since specific installations may vary, this section is intended for reference only, and provides generic information
for the installation engineer. The most important single factor when selecting such devices is a thorough
knowledge of local wiring protocols on the equipment to be installed.
Rectifier and bypass input power supply lines
Install the appropriate protective devices on the mains input power supply distribution line. These devices are
designed to provide over-current, short circuit, and isolation protection, and to trip in the event of back-feed.
Some of the important aspects that must be taken into consideration when selecting these devices are listed
below:
•
Power cable current carrying capacity
•
System overload capacity
•
Short circuit capacity of the upstream power distribution
The use of external protection devices (use recommended models only, or alternative components with
equivalent or superior specifications) is required in order to satisfy the UPS KAIC (Kilo Ampere Interrupting
Capacity) requirements.
Note
Split Bypass configuration
If the UPS adopts the split bypass configuration, independent protective devices must be used on the rectifier
input and bypass input distribution lines. The rectifier input and bypass input must use the same neutral line. It
is not necessary to install differential protection devices upstream of the UPS, however, if such devices are
required in order to comply with local regulations, it is important to be aware that, if separate differential circuit
breakers (DCB) are installed on the input and bypass power lines, they may trip unexpectedly, interrupting the
power supply to the unit. Therefore, if it is necessary to install a DCB, a single device should be used for both the
primary and bypass inputs.
In the case of IT networks, the UPS external input power distribution line must be fitted with a 4-pole
protective device.
Earth fault protection
When starting up the UPS, the transient and steady state ground leakage currents must be taken into account
when the upstream input power supply is fitted with a residual current circuit breaker (RCCB).
The RCCB must meet the following requirements:
•
Be sensitive to the DC uni-directional pulse (Class A) of the whole distribution network.
•
Be sensitive to the transient state current pulse.
•
Have an adjustable average sensitivity which is approximately 0.3A - 3A.
The RCCB symbols are depicted in Figure 4-1:
Figure 4-1 RCCB Symbols
A differential device installed on the primary and bypass inputs supply senses the sum of all the earth leakage
currents, in both the UPS and the load or loads connected to it.
To avoid spurious operation, the following factors must be taken into consideration when selecting differential
protection devices for installation on input lines:
1. The nominal value of ID must take into account the earth leakage current of the UPS and the load under normal
operating conditions: ID = IDUPS + load leakage current.
N.B. The maximum limit for UPS ground leakage current is 5% of nominal input current (see
IEC/EN62040-1+A1:2013)
2. Be of a delayed operation type (greater than 300 mS);
3. The type of differential switch used must conform to product regulation IEC/EN62040-1+A1.:2013
