6 System components
6.1 External power supply
PXR Electronic trip unit 01/21 MN012005EN www.eaton.com 39
6 System components
6.1 External power supply
The auxiliary power supply to the PXR trip unit enables its full functionality,
even if the circuit breaker is open, or if the circuit breaker is operating with a
load that is so low (less than 15 % of I
n
) that the current transformers are
unable to provide sufficient power for the trip unit’s own power supply.
An external power supply is required for the following functions:
• Communication link,
• Relay module functionality,
• Residual-life indicator (only on the PXR25)
• Event logging
The auxiliary power supply has to be connected to the interface module of
the circuit breaker.
The current protection functions do not require any auxiliary power supply.
Table 19: External power supply requirements
6.2 Electromagnetic compatibility
The electromagnetic compatibility of electronic components in circuit-
breakers is certified according to the product standard IEC/EN60947-2.
The configurations tested are standard configurations of typical applications.
However, in practical applications, electromagnetic interferences cannot be
completely
excluded under
worst case
conditions. In such
critical applications,
the immunity of switch gear and control gear can be further improved.
EATON recommends in such critical applications the use of a snap-on ferrite
(e.g. type WE 74271132 by Würth Electronic). The ferrite should be installed
on the external 24 V DC power line in close proximity to the circuit-breaker.
Value
Rated control voltage U
s
24 V DC
Tolerance ±20 %
Maximum current consumption 0.1 A
Fuse protection 2A
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