The consumer-service connection

From Electrical Installation Guide

Service components and metering equipment were formerly installed inside a consumer’s building. The modern tendency is to locate these items outside in a weatherproof cabinet

In the past, an underground cable service or the wall-mounted insulated conductors from an overhead line service, invariably terminated inside the consumer’s premises, where the cable-end sealing box, the utility fuses (inaccessible to the consumer) and meters were installed.

A more recent trend is (as far as possible) to locate these service components in a weatherproof housing outside the building.

The utility/consumer interface is often at the outgoing terminals of the meter(s) or, in some cases, at the outgoing terminals of the installation main circuit-breaker (depending on local practices) to which connection is made by utility staff, following a satisfactory test and inspection of the installation.

A typical arrangement is shown in Figure C6.

Fig. C6 – Typical service arrangement for TT-earthed systems

LV consumers are normally supplied according to the TN or TT system, as described in chapters LV Distribution and Protection against electric shocks and electrical fires. The installation main circuit-breaker for a TT supply must include a residual current earth-leakage protective device. For a TN service, overcurrent protection by circuit-breaker or switch-fuse is required

A MCCB -moulded case circuit-breaker- which incorporates a sensitive residual-current earth-fault protective feature is mandatory at the origin of any LV installation forming part of a TT earthing system. The reason for this feature and related leakage-current tripping levels are discussed in Implementation of the TT system.

A further reason for this MCCB is that the consumer cannot exceed his (contractual) declared maximum load, since the overload trip setting, which is sealed by the supply authority, will cut off supply above the declared value. Closing and tripping of the MCCB is freely available to the consumer, so that if the MCCB is inadvertently tripped on overload, or due to an appliance fault, supplies can be quickly restored following correction of the anomaly.

In view of the inconvenience to both the meter reader and consumer, the location of meters is nowadays generally outside the premises, either:

  • In a free-standing pillar-type housing as shown in Figures C7 and C8
In this kind of installation it is often necessary to place the main installation circuit-breaker some distance from the point of utilization, e.g. saw-mills, pumping stations, etc.
Fig. C7 – Typical rural-type installation
The main installation CB is located in the consumer’s premises in cases where it is set to trip if the declared kVA load demand is exceeded.
Fig. C8 – Semi-urban installations (shopping precincts, etc.)
  • In a space inside a building, but with cable termination and supply authority’s fuses located in a flush-mounted weatherproof cabinet accessible from the public way, as shown in Figure C9
The service cable terminates in a flushmounted wall cabinet which contains the isolating fuse links, accessible from the public way. This method is preferred for esthetic reasons, when the consumer can provide a suitable metering and main-switch location.
Fig. C9 – Town centre installations
  • For private residential consumers, the equipment shown in the cabinet in Figure C6 is installed in a weatherproof cabinet mounted vertically on a metal frame in the front garden, or flush-mounted in the boundary wall, and accessible to authorized personnel from the pavement. Figure C10 shows the general arrangement, in which removable fuse links provide the means of isolation
Fig. C10 – Typical LV service arrangement for residential consumers

In the field of electronic metering, techniques have developed which make their use attractive by utilities either for electricity metering and for billing purposes, the liberalisation of the electricity market having increased the needs for more data collection to be returned from the meters. For example electronic metering can also help utilities to understand their customers’ consumption profiles. In the same way, they will be useful for more and more power line communication and radio-frequency applications as well.

In this area, prepayment systems are also more and more employed when economically justified. They are based on the fact that for instance consumers having made their payment at vending stations, generate tokens to pass the information concerning this payment on to the meters. For these systems the key issues are security and inter-operability which seem to have been addressed successfully now. The attractiveness of these systems is due to the fact they not only replace the meters but also the billing systems, the reading of meters and the administration of the revenue collection.