Cable laying under the PUE code

Author: Viacheslav Yurdyk, quality engineer at LK Energy Group.
Acceptance of equipment at the factory (quality control department) and technical supervision on electrical installation sites.

Short answer

A cable up to 20 kV is laid in a trench at a depth of at least 0.7 m below the finished ground level [ПУЕ, п. 2.3.60]. For 27 and 35 kV — at least 1.0 m, for 110–330 kV — 1.5 m. Across arable land and at crossings of streets and squares — at least 1 m, even for a cable up to 20 kV.

But depth is only the first of four figures you need before earthworks begin. The other three: the distance to building foundations (at least 0.6 m and not less than the laying depth), the distance to tree trunks (1.5 m) and the distance to pipelines (from 0.5 to 3.0 m depending on what is in the pipe). An error in any of them surfaces at acceptance — and is corrected by digging the route up again.

Depth: four figures

What is being laid	Depth below finished ground level
Cable line rated up to 20 kV	at least 0.7 m
Cable line rated 27 and 35 kV	at least 1.0 m
Cable line rated 110–330 kV	at least 1.5 m
Cable line up to 20 kV across arable land, crossings of streets and squares	at least 1 m

[п. 2.3.60]

Where the depth may be reduced [ibid.]: at intakes into structures and at crossings with underground structures, over sections up to 5 m long, provided the cable is protected against mechanical damage — down to 0.5 m for cable lines up to 35 kV and down to 1 m for 110–330 kV.

🔑 Why 1 m across arable land is not over-caution. At that depth the land above the cable may be used for crops [ibid.]. So the rule does not prohibit farming — it is precisely what permits it, unlike the «as it turned out» 0.4 m after which the plough finds the cable by itself.

Distances: to what and how far

To buildings and structures [п. 2.3.60]: - horizontally from the outermost cable to the edge of the buried part of the foundations of above-ground buildings — equal to the laying depth, but not less than 0.6 m; - from the walls of tunnels and service ducts — at least 0.5 m; - 🔴 laying cables in trenches beneath the foundations of buildings and structures is prohibited.

To trees and shrubs [п. 2.3.62]: - to tree trunks — at least 1.5 m. This may be reduced only by agreement with the organisation responsible for the green plantings, and provided the cables are laid in ducts by trenchless boring or horizontal drilling; - within a green zone with shrub plantings — down to 0.75 m.

To pipelines, running parallel [п. 2.3.63]:

To what	Minimum horizontal clearance
water main up to 300 mm in diameter	0.5 m
water main over 300 mm, pipelines carrying liquids laid without ducts	1.0 m
sewers, drainage, stormwater	0.5 m
gas pipeline, low pressure (up to 0.049 MPa)	1.0 m
gas pipeline, medium pressure (0.049–0.294 MPa)	1.5 m
gas pipeline, high pressure (0.294–0.588 MPa)	2.0 m
gas pipeline, high pressure (0.588–1.177 MPa)	3.0 m
walls of a heating duct	1.0 m

🔴 Separately, and this is broken often: running cables parallel above or below pipelines is prohibited [ibid.]. The cable must run beside the pipe, not «one storey up».

In congested urban development the distances to pipelines (other than gas and flammable liquids) may be reduced: down to 0.25 m if cables up to 35 kV are run in ducts, down to 0.5 m if they are laid without special protection [ibid.].

Between cables in one trench [п. 2.3.61]: - 0.1 m — between power cables up to 10 kV and between them and control cables; - 0.25 m — between cables of 20–35 kV and between them and cables rated below 20 kV; - 0.5 m — between cables of 110–330 kV; - 0.5 m — between cables up to 35 kV operated by different organisations, and from power cables to communication cables (this may be reduced to 0.25 m subject to an electromagnetic interference calculation and protection against damage during a short circuit); - the spacing between control cables themselves is not regulated.

Crossings: when the route runs across

Crossing other cable lines [п. 2.3.69]: separation by a layer of soil at least 0.5 m thick. In congested development, for cables up to 35 kV, this may go down to 0.15 m provided they are separated by concrete slabs or ducts over the whole crossing section plus 1 m on each side; communication cables are then placed above the power cables.

Crossing pipelines, including oil and gas pipelines [п. 2.3.70]: vertically from the outermost cables to the pipeline — at least 0.5 m for cable lines up to 35 kV. It may be reduced to 0.15 m provided the cable is run in ducts over the crossing section extending at least 2 m on each side.

Crossing heating mains [п. 2.3.71]: a clearance of at least 0.5 m, in constrained conditions — at least 0.15 m. The heating main over the crossing section (plus 2 m on each side) must be insulated so that the soil temperature does not rise by more than 10 °C above the summer maximum and by more than 15 °C above the winter minimum.

Crossing railways and roads [п. 2.3.72]: in tunnels, ducts or pipes across the full width of the right of way, at a depth of at least 1 m below the track or road bed and at least 0.5 m below the bottom of drainage ditches. Where there is no right of way — over the crossing section plus 2 m on both sides.

🔑 What this means in practice. Almost every «the distance cannot be maintained» has a way out in the Rules — but the way out costs money: a duct, a slab, thermal insulation, drilling. So agreeing the route at design stage is cheaper than looking for concessions at acceptance.

Protecting the cable in the trench

For cable lines up to 20 kV, above the initial layer of soil, contractors lay warning tape at 0.25 m above the top of the cable — or, at the same height, a single course of solid clay bricks across the route, or polymer sheets [п. 2.3.59].

bricks or polymer sheets for cables up to 20 kV are used only where other underground services make frequent excavation likely;
if there is a single cable in the trench, the tape is laidalong the cable axis; if there are more, the edges of the tape must extend beyond the outermost cables by at least 0.05 m;
🔑 a second warning tape is laid along the centre of the trench, 0.25 m above the first, for cable lines up to 20 kV supplying category I loads and the special group of category I, and for cable lines running from a substation to distribution points or transformer points.

That last point is worth re-reading if you are building the supply to your own production: the line from the substation to your distribution or transformer point is marked with a double tape under the Rules. It is a direct signal to any excavator operator, and it costs pennies compared with downtime.

Cross-section: why a «kW → mm²» table does not exist

The most common question — «what cross-section do I take for this load» — has no single-figure answer, and the Rules say so in the very first clause of the chapter.

The cross-section is selected for heating. But if any other condition requires a larger cross-section, the largest of them is taken [п. 1.3.1]. The other conditions are:

thermal and electrodynamic withstand under short-circuit currents;
voltage losses and voltage deviation;
mechanical strength;
protection against overload.

So heating is the minimum, not the answer. A cable that «by the table» carries the current may fail to withstand a short circuit or cause an unacceptable voltage drop on a long line — and then the cross-section is increased.

🔑 How to talk to your contractor. The question «where did this cross-section come from» has four valid answers, and «from the table of permissible currents» is only one of them. If the line is long, the second question is about voltage losses; if the load is large — about short-circuit withstand.

A new feature of the 2026 edition worth knowing: chapter 1.3 introduces the term «dynamic line rating» — the maximum permissible 30-minute value of transmission capacity, taking into account wind direction and speed, air or soil temperature, solar radiation and precipitation along the route [глава 1.3, терміни]. It is a move from a fixed table towards calculation based on actual conditions.

Testing a cable line

After laying — before energising, always, at any voltage. After that the interval depends on the type of line [ПТЕЕС, додаток 2, таблиця 11]:

Type of cable line	Interval
Cable lines up to 1 kV	after laying and after repair — before energising
Cable lines 2–35 kV, first two years of service	once a year
Cable lines with no damage found during testing in the first two years	once every 2–3 years
Cable lines supplying especially critical loads	once a year
Cable lines with a high likelihood of mechanical and corrosion damage (where construction work is under way)	once a year
Cable lines in enclosed routes	once every 3 years
Cable lines 110–150 kV	first time after 3 years, then once every 5 years

🔑 The logic worth explaining to the client. For the first two years the line is tested annually — this is when installation errors and damage from construction machinery come to light. If two years pass cleanly, the interval drops. In other words, careful laying saves not only nerves but also money on testing in later years.

Frequently asked questions

At what depth is a cable laid under PUE?

Below the finished ground level of the site: at least 0.7 m for cable lines up to 20 kV, 1.0 m for 27 and 35 kV, 1.5 m for 110–330 kV. Across arable land and at crossings of streets and squares — at least 1 m [п. 2.3.60].

Can it be shallower if a service is in the way?

Yes, but only locally: at intakes into structures and at crossings with underground structures, over sections up to 5 m long, provided the cable is protected against mechanical damage — down to 0.5 m for cable lines up to 35 kV [п. 2.3.60]. The depth may not be reduced along the whole route.

What cable cross-section does PUE require?

There is no single «load → cross-section» table. The cross-section is selected for heating and then checked for thermal and electrodynamic withstand under short circuit, for voltage losses and deviation, for mechanical strength and for overload protection — and the largest of the results is taken [п. 1.3.1]. The tables of permissible continuous currents in chapter 1.3 give only the first of these four results.

What is the distance from a cable to a building foundation?

Horizontally — equal to the laying depth, but not less than 0.6 m. From the walls of tunnels and service ducts — at least 0.5 m. Laying a cable in a trench beneath a foundation is prohibited [п. 2.3.60].

How far must one keep from a tree?

From trunks — at least 1.5 m; in a green zone with shrubs — 0.75 m. Less is allowed only by agreement with the organisation responsible for the plantings and provided the cable is laid in ducts by trenchless boring or horizontal drilling [п. 2.3.62].

What is the distance from a cable to a gas pipeline?

It depends on the pressure: 1.0 m — low (up to 0.049 MPa), 1.5 m — medium (up to 0.294 MPa), 2.0 m — high (up to 0.588 MPa), 3.0 m — high (up to 1.177 MPa) [п. 2.3.63]. For gas pipelines and flammable liquids the concessions for congested development do not apply.

Can a cable be run directly above a pipe?

No. Running cables parallel above or below pipelines is prohibited [п. 2.3.63]. Crossing is allowed — with a vertical clearance of at least 0.5 m, or at least 0.15 m if the cable is in a duct extending 2 m either side of the crossing [п. 2.3.70].

What is warning tape for and at what height must it be?

So that the excavator sees the warning before it reaches the cable. For cable lines up to 20 kV the tape is laid 0.25 m above the top of the cable; if there are several cables, the edges of the tape extend beyond the outermost ones by at least 0.05 m [п. 2.3.59].

When are two warning tapes required?

For cable lines up to 20 kV supplying category I loads and the special group of category I, and for lines from a substation to distribution or transformer points — a second tape is laid along the centre of the trench 0.25 m above the first [п. 2.3.59].

Are bricks above the cable mandatory?

No. Clay bricks or polymer sheets for cables up to 20 kV are used only on sections where other underground services make frequent excavation likely [п. 2.3.59]. Elsewhere warning tape is enough.

What spacing is required between cables in one trench?

0.1 m — between power cables up to 10 kV and between them and control cables; 0.25 m — for 20–35 kV; 0.5 m — for 110–330 kV, and also between cables up to 35 kV operated by different organisations, and to communication cables [п. 2.3.61].

How is a road or railway crossed with a cable?

Only in tunnels, ducts or pipes across the full width of the right of way, at a depth of at least 1 m below the track or road bed and at least 0.5 m below the bottom of drainage ditches. If there is no right of way — over the crossing section plus 2 m on both sides [п. 2.3.72].

How often are cable lines tested?

After laying — always before energising. After that, for cable lines 2–35 kV: annually for the first two years; if no damage was found — once every 2–3 years; for lines to especially critical loads and for routes where construction work is under way — annually; in enclosed routes — once every 3 years [ПТЕЕС, додаток 2, таблиця 11].

What insulation resistance should a cable have?

The standards and test methods for cable lines are set out in annex 1, table 5 to PTEES, and the normative values in annex 2. The figure depends on the voltage, the insulation type and the kind of check, so «a single number» does not work here either; the measurement is carried out by an accredited laboratory and recorded in a test report.

Let us size the cable part together with the switchgear

LK Energy carries out electrical installation work and manufactures 0.4–35 kV switchgear at its own plant in Odesa. Send a single-line diagram or a completed data sheet — we will select the cross-section, the laying method and the switchgear configuration for your site.

This material is provided for information only and is neither an offer nor legal advice. We do not publish the full text of the Rules — only quotations with clause numbers; obtain the official text from the source named above.

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Cable laying under the PUE code: methods, cross-sections, testing