Surge protection for meter locations

Optimized surge protection in the residential building sector

Whether in old or new buildings, detached, terraced or semi-detached houses ... meter cabinets downstream of the house connection box are nowadays predominantly equipped with a 5-pole busbar system. Smaller apartment buildings also benefit from this system, which allows a space-saving modular design and uncomplicated contacting of switching and installation devices in the lower power range. The distance between the busbars is 40 mm.

This 40 mm busbar system is also the ideal basis for installing a lightning and surge arrester. While surge protection has always been required in the event of danger to human life due to the consequences of an overvoltage, the new regulation now also requires overvoltage protection in residential buildings and small offices, for example, if equipment of overvoltage protection categories I or II (e.g. household appliances or IT systems) is connected to the fixed installation. Objects that react more sensitively to mains disturbances require a higher level of safety, which is also anchored in parts -443 and -534 of DIN VDE 0100.

Let's take a look at a modern meter cabinet.

Below is a schematic representation from the informative Appendix E of VDE-AR-N 4100.

Terminology
1 AAR (system-side connection room) To accommodate main line indicator terminals (HLAK) or main switches for connecting the supply line to the downstream circuit distribution board - or a residual current device (RCD) to protect the supply line to the circuit distributor.
2 ZF (meter field) Consists of the BKE (mounting and contacting device) to accommodate electronic household meters (eHZ) and the RfZ (room for additional applications such as SMG - smart meter gateway, or the metering system).
3 NAR (network-side connection room) Space for the busbar system, the selective main circuit breaker (SH circuit breaker), the SPD (Surge Protection Device) type 1 or the overcurrent protection device for the power supply of the measuring system.
4 APZ (connection point meter location) Interface between house transfer point (HÜP) and meter location.

Here, the use of a combined arrester in the pre-metering area, i.e. in the grid-side connection compartment where the 5-pole 40 mm busbar system is also located, is ideal. Although special requirements must be met upstream of the metering device in accordance with the application guideline and the grid operator's technical connection conditions based on it, its use there is rewarded with optimum performance in addition to uncomplicated installation. The direct contact with the busbar results in the best possible protection level values and, in the version with certified test class T3 in accordance with IEC 61643-11 (device protection), also the best possible protection for the measuring device. In particular, this increases the reliability and availability of the entire electrical installation in the building.

The requirement to place the SPD as close as possible to the building entry point is also taken into account. According to the standard, the meter cabinet must be installed as close as possible to the house connection box. Depending on the type of grid provided on site by the grid operator, the building feed-in then looks as follows:

TNC-S network - Recommended PEN distribution in the house connection box (HAK)

TNC-S network - Permissible PEN distribution in the mains-side terminal compartment (NAR)

TT network

Selection of the SPD required for my object according to the standard

A look at the basic lightning protection standard can help here. Part 1 of IEC 62305 (VDE 0185-305-1) deals, among other things, with the differentiation of various sources of damage for a structure and allows an initial assessment of the threat level.

S1 = Lightning strikes the structure
S2 = Lightning strike near the structure
S3 = Lightning strike in the inserted cable
S4 = Lightning strike near the inserted cable

Selection guide

Future-oriented equipment

The specifications of the grid operators, which are based on the VDE application rule, stipulate the voltage tap-off from the grid-side connection compartment (NAR) before the disconnecting device for the connection user system. The new ZPAC PRO scores particularly well for meter cabinets with two selective main circuit breakers (SH) in the NAR.

The ZPAC PRO offers an integrated voltage tap in two versions: on the one hand for supplying components in the meter terminal point (APZ) and on the other hand for supplying the RfZ.
This room for additional applications is part of the meter panel (ZF) and is used by the grid operator for the spatial accommodation of measuring equipment, such as a smart meter gateway. The 3-pin plugs used correspond exactly to the specifications of VDE-AR-N 4100.

An overcurrent protection device integrated in the ZPAC PRO has also been provided and meets the requirements of short-circuit protection devices in the main power supply system upstream of the measuring device.
The immediate availability of a spare fuse has also been taken into account, just in case. It is recessed in a small trough directly on the product and is therefore always ready to hand.

Optionally available pre-assembled connection cables of different lengths make it easier to connect the measuring system in practice. All these features are protected against unauthorized access during operation by the sealed protective cover, as are the contacts underneath the plug-in protection modules.

With reference to the VDE-AR-N 4100 application rule, the ZPAC PRO also provides remote signaling for commercially used systems and systems with increased security requirements. The latter are defined in more detail in DIN VDE 0100 Part 443, e.g. systems for security purposes, hospitals, public facilities, but also residential buildings if sensitive electronic devices are operated in them ... and this can also be assumed according to the note in the standard.

The potential-free changeover contact is used for status monitoring and can be integrated as a binary output in modern building management or smart home systems, for example.

Available versions