Voltage levels: low (NN), high (VN) and extra-high (VVN)

Under the Czech Energy Act the electricity distribution system consists of lines and equipment at 0.4/0.23 kV, 1.5 to 35 kV (for example 10, 22 or 35 kV) and 110 kV. The transmission system consists of 400 kV, 220 kV and selected 110 kV lines. In practice people speak of low (NN), high (VN) and extra-high voltage (VVN) levels.

How to tell them apart

• NN, low voltage: up to 1 kV, in homes 400 V between phases and 230 V at the socket; houses and flats are connected at NN,
• VN, high voltage: above 1 kV, distributors quote a range up to 52 kV; runs between villages and to transformer stations,
• VVN, extra-high voltage: 110 kV and above; backbone lines between regions.

A transformer station steps electricity down from VN to NN, which feeds the houses' service connections.

Connection and protection zone

A low-voltage connection can be overhead, using insulated conductors or an aerial cable from a pole, or an underground cable. An overhead connection ends in the main fuse box of the building, an underground one in the main cable box. Under the Energy Act, overhead NN lines have no protection zone, so they restrict a plot less than VN lines, which have 1 to 7 m on each side depending on the conductors, and more for lines built before the end of 1994. Safe working distances under technical standards still apply near NN lines.

Connection fee

The voltage level also affects the connection fee. The share of connection costs is calculated at NN from the rating of the main circuit breaker before the meter in amperes, and at VN and VVN from the agreed capacity in MW.

Can you build under a VN line?

Within the protection zone of an overhead line, building is possible only with the consent and under the conditions of its owner; the distributor may refuse. It is therefore wise to find out the line's position and zone width before buying a plot.