Enatel DC System Manual
Page 7 of 31
3.3
AC Cabling
The AC cables are clearly labelled at the rear of the system (see Fig 3). The AC cable provided
is 2.5mm
2
cables and suitable terminals should be used.
AC connection internally is via 6.4mm QC tabs. Longer cables can be easily fitted by replacing
the existing cable. Ensure that the AC colour coding is correct for the country of fitment:
Fig 3, AC Cable Detail
Connections should allow for a maximum single phase AC supply of 15A (@ 175VAC) (see next
section).
The AC earth is internally bonded to the system chassis.
DC Common is connected to the AC earth through the placement of the PCB connecting the
backplane to the distribution. Alignment depends on required earthing connection. Please see
the DC earthing section of this manual for more detail.
Note: Please refer Appendix 3 for AC Input Transient Protection.
3.3.1 Upstream Over-current Protection
There are two considerations to take into account when selecting an appropriate fuse/circuit
breaker.
-
The upstream protection should protect the downstream cable from overload situations.
-
Discrimination should be maintained with the downstream device fuses.
(i) Cable Rating
The maximum current drawn by the DC power system is 15A (5A per rectifier at a minimum
input voltage of 175V
ac
and full output power). The upstream protection device must be able to
supply this load under all conditions without tripping. Therefore, typically at least 20%
headroom is allowed for in the protection device, making its minimum rating 18A.
Note: The current carrying capacity of cables is dependent on the type of cable used. Please
check with your local supplier and local regulations for appropriate sizing.
For convenience, the system is supplied with a 1.0m long, 3-core, 2.5mm
2
flex already
attached. This has a current carrying capacity of 20A.
(ii) Discrimination
Discrimination ensures that the upstream circuit breaker or fuse does not blow if a rectifier input
fails (short circuit). Therefore it is important to ensure the upstream protection discriminates
with the internal fuse of the rectifier. The fuse used in the RM848 is a slow-blow 10A fuse. The
tripping curve for this is shown in Appendix 2 at the rear of this manual.
