ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 184)

electrical hazards. The protecting devices are called “circuit breakers” (or fuses for

old networks). They may be of several types. Each circuit breaker has specific char-

acteristics concerning the attenuation of the PLC signal conveyed over the cable.

Figure 8.12 illustrates an example of a closed (on the left), open (in the middle),

and front elevation (on the right) circuit breaker panel. The devices connected to the

panel are identified in it.

Attenuation on an Electrical Network

We have seen that, beyond a linear length of 300m (in a wound electrical cable, the

self-induction phenomenon does not give the same results), the useful throughput

quickly falls, due to the signal attenuation, to such an extent that it becomes too low

to offer a satisfactory quality of service for upper layer applications.

Each cable has a different section and impedance characteristics inducing differ-

ent PLC signal attenuations. At 100m, the attenuation of the HNS33S33 cable used

in LV public networks is 14 dB for a PLC signal at the frequency of 30 MHz.

There are several types of electrical wirings for an LV (low voltage) installation

in a building:

•

Cables called conductors, phase, neutral, and ground are placed in the walls

or in individual sheaths but are not grouped in one single sheath. This wiring

type induces a higher electromagnetic emission in the immediate environ-

ment. Due to the loss of these electromagnetic emissions, the PLC signal prop-

agation over the cables is subjected to a rather high attenuation. These cables

are typically found in installations under the H07 V-U or H07 V-R (rigid con-

ductors), H07 V-K (flexible conductors), P/N for conduit, molding, or plinth

mountings.

•

P, N, and G cables are installed together in a twisted way with the ground

cable in the middle of the twist inside a sheath. A much better propagation of

the PLC signal is achieved with this type of cable since the cables induce elec-

tromagnetic couplings between themselves. In addition, just like the telephone

cable, the twisted arrangement allows better guidance of the PLC signal and

makes it possible to avoid attenuations caused by electromagnetic leakage in

the immediate environment. The signal is still relatively confined in the sheath

and achieves better performance, with respect both to the distance and bit

rate. These cables are typically found in installations under FR-N 05 VV-U or

R (rigid cables), A05 VV-F or H07 RNF (flexible cables), P/N for surface

mountings, in air spaces, moldings, plinths, or conduits.

•

P, N, and G cables are twisted together by the electrical installer before plac-

ing them in raceways or in the building walls. This wiring type provides a

good propagation of the PLC signal and very little loss due to electromagnetic

emissions.

Recommended Cable Length in an Average Domestic Installation

If we take the case of an average house (i.e., a 100-m² F4 single-story house or a 65-m²

T3-T4 apartment), the general cable length between the circuit breaker panel and the out

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