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APPENDIX 1
Proximity between high-voltage plants and metal piping
High-voltage plants in the proximity of metal pipelines surrounded by an insulating coating or otherwise insulated to
earth may under certain circumstances give rise to such electrical influences that it is dangerous to touch the piping
and other electrically conductive parts in contact with the piping.
I – Electrostatically influenced plants
In case of electrostatic influence from a high-voltage overhead wire to a pipeline placed insulated to earth, the
current from the piping to earth through a negligible impedance may not exceed 5mA. For a.c. high-voltage overhead wires, this provision may be deemed to be met when one of the following conditions
is met:
1) The horizontal distance between the pipeline and the high-voltage overhead wire is minimum 50 metres and
the length of the pipeline does not exceed 500 metres.
2) The length of the pipeline within the distance mentioned in 1) above does not exceed 150 metres.
3) The operating voltage of the high-voltage overhead wire does not exceed 60kV.
If there is a risk that the current will exceed 5mA, earth electrodes must be connected to the pipeline. Minimum one
(1) electrode must be established for every 500 metres of pipe length.
II – Touch voltage, UTp
The voltage a high-voltage wire can induce on a proximate insulated pipeline is defined below as the voltage
difference UTp between:
1) Parts of the piping that are accessible for touch at the same time.
2) Parts of the piping and earth accessible for touch.
3) Parts of the piping accessible for touch and other electrically conductive parts with connection to earth
that are accessible for touch at the same time.
4) Parts of the piping that are accessible to touch and circuits belonging to high-voltage and low-voltage
installations connected to neutral earth and located less than 1 metre from the piping.
III – Electromagnetic induction under normal operation of high-voltage plants
The induced voltage UTp on a proximate insulated pipeline may not exceed 50V under normal operation.
For three-phase high-voltage wires this requirement may be deemed to be met when one (1) of the following
conditions is met:
1) The operating voltage of the high-voltage wire does not exceed 40kV.
2) The horizontal distance between high-voltage wire and pipeline is minimum 200 metres.
IV – Electromagnetic induction in case of faults on high-voltage plants
The induced voltage UTp on a proximate insulated pipeline may not exceed the value in Figure 1 in case of faults on
the high-voltage plant.
If the disconnection time exceeds 10 seconds, UTp may not exceed 50V.
For three-phase high-voltage wires this requirement may be deemed to be met when the horizontal distance
between the high-voltage wire and the pipeline is minimum 1000 metres.
In networks where single earth faults are disconnected within 5 seconds or where the network is resonant earthed,
double earth faults need not be considered.
V – Influences in case of increased earth potential
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In case of earth faults on a high-voltage overhead wire or in a high-voltage station, the increased earth potential
surrounding the earthed pylon of the wire or surrounding the high-voltage station must not cause a higher voltage
difference between parts of proximate insulated piping accessible for touch and earth than stated in Figure 1.
If the disconnection time exceeds 10 seconds, UTp may not exceed 50V.
For three-phase high-voltage plants this requirement may be deemed to be met when one (1) of the following
conditions is met:
1) The operating voltage of the high-voltage plant does not exceed 60kV.
2) The distance from piping to the exterior limit of the high-voltage station is minimum 50 metres and the
distance from the piping to the earthed pylon of the high-voltage overhead wire is minimum 15 metres.
VI – Measures to protect against touch danger
The maximum voltage differences fixed in items III, IV and V may be exceeded if measures are taken to eliminate or
limit the effects of the voltage differences to an extent that does not exceed the impact of the permissible voltage
differences, cf. Figure 1.
Figure 1 Maximum permissible touch voltage
Maximum permissible touch voltage UTp
Voltage
1 000
900
800
700
600
500
400
300
200
100
0
10
100
1 000
10 000
Time in ms
Source EN 50522:2010
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