Clipsal C-Bus Especificações descarregar pdf (Página 47)

1C. C-Bus Hardware

1.1 Power Supply

The C-Bus power supply is a switch mode device, which means it is efﬁcient and compact. It converts

mains voltage into a usable C-Bus voltage of 36Vd.c.. It is the C-Bus power source, providing power

to each unit on the network.

The C-Bus system operates at an Extra Low Voltage (ELV) level. The minimum voltage required by

each device on the bus is 15Vd.c.. However, a voltage this low may cause communication to be

unstable. Therefore, it is strongly recommended that the C-Bus voltage be at least 20Vd.c.

The resistance of a typical C-Bus Unshielded Twisted Pair (UTP) conductor is 90Ω/km. The typical

current requirement of a C-Bus device is 18mA. Therefore, if one device is connected to the end of

one kilometre of C-Bus cable (Figure 1), the voltage drop would be 90 × 18 × 10

–3

or 1.6V.

Figure 1 – Voltage drop over one kilometre of C-Bus cable (Approximately 18 mA per device).

In an installation, power supplies should be distributed evenly along the C-Bus, rather than just at one

end, in order to minimise system voltage drops.

Number of Required Power Supplies

The number of power supplies needed in a C-Bus installation depends upon:

• the power supply output current

• the number and type of devices on the network

• the location of the devices in relation to the power supplies.

While the rst two points are easily measured, the third is more subjective. Power supplies should

be placed to minimise voltage drop across the network, reducing power loss. As a general rule, one

power supply is required for every 17 C-Bus units that draw 18mA each.

Output Current Limiting

One of the many advantages of the C-Bus ELV is that connections can be made while power is

applied to the network. (This applies to 36V C-Bus input units, but not units with mains voltage

connections such as dimmers and relays). Should a short circuit occur on the C-Bus, the power

supply current limiting and overload protection feature, provides protection from damage for an

indeﬁnite period of time.

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Clipsal C-Bus Especificações Página 47