Micom P721, Technical Manual

Page: 37 / 334

Handling, Installation and Case Dimensions P72x/EN IN/C21
MiCOM P721/P723 Page 9/10
To insure the insulation of the terminals and to respect the security and safety instructions,
an isolated sleeve can be used.
We recommend the following cable cross-sections:
−
Auxiliary sources Vaux: 1.5 mm²
−
Communication Port see paragraph 6.2
−
Other circuits 1.0 mm²
Because of the limitations of the annular terminals, the maximum wire cross-section which
can be used for the connector blocks (for current inputs and signals) is of 6mm² by using non
-insulated annular terminals. When only pre- insulated terminals can be used, the maximum
wire cross-section is reduced to 2, 63 mm² per annular terminal. If a more significant wire
cross-section is necessary, two wires can be put in parallel, each one finished by a separate
annular terminal.
All the terminal blocks used for connections, except of the port RS485, must be able to
withstand a nominal voltage of minimum 300V peak value.
We recommend to protect the auxiliary source connection by using a fuse of type NIT or TIA
with a breaking capacity of 16A. For security reasons, do never install fuses in current
transformers circuits. The other circuits must be protected by fuses.
6.2 Communication port RS485
Connections to RS485 is made using annular terminals. It is recommended that a two core
screened cable, is used with a maximum total length of 1000 m or a200nF total cable
capacitance.
Typical specification:
−
Each core: 16/0.2 mm copper conductor, PVC insulated.
−
Nominal conductor area: 0.5 mm² per core
−
Screen: Overall braid, PVC sheathed
−
Linear capacitance between conductor and earth: 100pF/m
6.3 Earthing
Each equipment must be connected to a local earth terminal by the intermediary of a M4
earth terminals. We recommend a wire of minimal section of 2.5 mm², with annular terminals
on the side of the equipment. Because of the limitations of the annular terminals, the
possible maximum section is of 6mm² by wire. If a larger section is necessary, one can use
cables connected in parallel, each one ending with an annular terminal separated on the side
of the equipment. One can also use a metal bar.
NOTE: To prevent any electrolytic risk between copper conductor or brass
conductor and the back plate of the equipment, it is necessary to take
precautions to isolate them one from the other. This can be done in
several ways, for example by inserting between the conductor and the
case a plated nickel or insulated ring washer or by using a tin
terminals.