UK Regs - Underground Cable

I always lay direct bury cables on a bed of sand unless the dirt is 100% clear of rocks and debris.

The marking tape especially one with a wire in it for exact locating is always a good idea.

Some engineers require a concrete cap above direct bury cables, 12 inches below grade. Some even want the cables encased in red concrete.

As specific requirements in the UK, I do not know mate. All of what you suggest is good practice.

As for my personal preference everything should be in conduit and in separate trenches. Random lay is a bitch to repair...

Thanks for the reply, but need to know if there is any specific requirement, especially as regards the marking.

For utility cables the National Electrical Safety Code is used in the US. The regulations from this document are rather complex as quoted below: (note: This is copyrighted material and cannot be duplicated. It is used here for educational purposes)

Part 3 Section 35.

Direct-Buried Cable

350. General

A. Section 33 shall apply to direct-buried supply cable.

B. Cables operating above 600 V to ground shall have a continuous metallic shield, sheath, or concentric

neutral that is effectively grounded.

EXCEPTION:

At a splice or joint, the current path of the metallic shield, sheath, or neutral shall be made continuous

but need not be concentric.

C. Cables meeting Rule 350B of the same supply circuit may be buried with no deliberate separation.

D. Cables of the same circuit operating below 600 V to ground and without an effectively grounded

shield or sheath shall be placed in close proximity (no intentional separation) to each other.

E. Communication cables containing special circuits supplying power solely to communications equipment

shall comply with the requirements of Rules 344A1 through 344A5.

F. Bonding should be provided between all above ground metallic power and communications apparatus

(pedestals, terminals, apparatus cases, transformer cases, etc.) that are separated by a distance of 1.8 m

(6 ft) or less.

G. All direct-buried jacketed supply cable meeting Rule 350B and all direct-buried communication cables

shall be legibly marked as follows:

The appropriate identification symbol shown in Fig 350-1 shall be indented or embossed in the

outermost cable jacket at a spacing of not more than 1 m (40 in). The symbol may be separate or

sequentially combined with other data, or symbols, or both, printed on the jacket. If the symbol is

sequentially combined, it shall be separated as indicated in Fig 350-1.

This rule became effective for cable installed on or after 1 January 1996.

EXCEPTION 1:

Cables with jackets that cannot be effectively marked in accordance with Rule 350G need not

be marked.

EXCEPTION 2:

Unmarked cable from stock existing prior to 1 January 1996 may be used to repair unmarked

direct-buried jacketed supply cables and communication cables.

H. The rules in this section also apply to direct-buried supply and communication cables installed in duct

that is not part of a conduit system.

351. Location and Routing

A. General

1. Cables should be located so as to be subject to the least disturbance practical. When cables are to

be installed parallel to and directly over or under other subsurface structures, the rules on separation

in Rule 353 or 354, as applicable, shall be followed.

1. Cables should be installed in as straight and direct a line as practical. Where bends are required,

the bending radius shall be sufficiently large to limit the likelihood of damage to the cable being

installed.

1. Cable systems should be routed so as to allow safe access for construction, inspection, and

maintenance.

1. The location of structures in the path of the projected cable route shall, as far as practical, be determined

prior to trenching, plowing, or boring operation.

B. Natural Hazards

Routes through unstable soil such as mud, shifting soils, corrosive soils, or other natural hazards

should be avoided. If burying is required through areas with natural hazards, the cables shall be constructed

and installed in such a manner as to protect them from damage. Such protective measures

should be compatible with other installations in the area.

C. Other Conditions

1. Swimming Pools

Supply cable should not be installed within 1.5 m (5 ft) of a swimming pool or its auxiliary equipment.

If 1.5 m (5 ft) is not attainable, supplemental mechanical protection shall be provided.

1. Buildings and Other Structures

Cable should not be installed directly under building or storage tank foundations. Where a cable

must be installed under such a structure, the structure shall be suitably supported to limit the likelihood

of transfer of a detrimental load onto the cable.

1. Railroad Tracks

a. The installation of cable longitudinally under the ballast section for railroad tracks should be

avoided. Where cable must be installed longitudinally under the ballast section of a railroad,

it should be located at a depth of not less than 1.27 m (50 in) below the top of the rail.

EXCEPTION:

Where this is impractical, or for other reasons, this clearance may be reduced by agreement

between the parties concerned.

NOTE:

Where unusual conditions exist or where proposed construction would interfere with existing

installations, a greater depth than specified above would be required.

b. Where a cable crosses under railroad tracks, the same clearances indicated in Rule 320A5

shall apply.

1. Highways and Streets

The installation of cable longitudinally under traveled surfaces of highways and streets should be

avoided. When cable must be installed longitudinally under the roadway, it should be installed in

the shoulder or, if this is not practical, within the limits of one lane of traffic to the extent practical.

1. Submarine Crossings

Submarine crossings should be routed, installed, or both, so they will be protected from erosion

by tidal action or currents. They should not be located where ships normally anchor.

352. Installation

A. Trenching

The bottom of the trench receiving direct-buried cable should be relatively smooth, undisturbed earth;

well-tamped earth; or sand. When excavation is in rock or rocky soils, the cable should be laid on a

protective layer of well-tamped backfill. Backfill within 100 mm (4 in) of the cable should be free of

materials that may damage the cable. Backfill should be adequately compacted. Machine compaction

should not be used within 150 mm (6 in) of the cable.

B. Plowing

1. Plowing in of cable in soil containing rock or other solid material should be done in such a manner

that the solid material will not damage the cable, either during the plowing operation or afterward.

1. The design of cable-plowing equipment and the plowing-in operation should be such that the cable

will not be damaged by bending, side-wall pressure, or excessive cable tension.

C. Boring

Where a cable system is to be installed by boring and the soil and surface loading conditions are such

that solid material in the region may damage the cable, the cable shall be adequately protected.

D. Depth of Burial

1. The distance between the top of a cable and the surface under which it is installed (depth of burial)

shall be sufficient to protect the cable from damage imposed by expected surface usage.

1. Burial depths as indicated in Table 352-1 are considered adequate for supply cables or conductors,

except as noted in a, b, or c following:

a. In areas where frost conditions could damage cables, greater burial depths than indicated

above may be desirable.

b. Lesser depths than indicated above may be used where supplemental protection is provided.

The supplemental protection should be sufficient to protect the cable from damage imposed

by expected surface usage.

c. Where the surface under which a cable is to be installed is not to final grade, the cable should

be placed so as to meet or exceed the requirements indicated above, both at the time of installation

and subsequent thereto.

Table 352-1

Supply Cable or Conductor Burial Depth

(See Rule 352D)

Voltage (Phase-to-phase)

Depth of burial

(mm) (in)

0 to 600 600 24

601 to 50 000 750 30

50 001 and above 1070 42

EXCEPTION:

Where conflicts with other underground facilities exist, street and

area lighting cables operating at not more than 150 V to ground may be buried at a

depth not less than 450 mm (18 in).

353. Deliberate Separations-Equal to or Greater than 300 mm (12 in) From Underground

Structures or Other

A. General

1. These rules apply to a radial separation of supply and communication cables or conductors from

each other and from other underground structures such as sewers, water lines, gas and other fuel

lines, building foundations, steam lines, etc., when separation is equal to or greater than 300 mm

(12 in).

NOTE:

For radial separation less than 300 mm (12 in) see Rule 354.

1. The radial separation should be adequate to permit access to and maintenance of either facility to

limit damage to the other.

B. Crossings

1. Where a cable crosses under another underground structure, the structure shall be suitably supported

to limit the likelihood of transfering of a detrimental load onto the cable system.

1. Where a cable crosses over another underground structure, the cable shall be suitably supported to

limit the likelihood of transfering a detrimental load onto the structure.

1. Adequate support may be provided by installing the facilities with sufficient vertical separation.

C. Parallel Facilities

Where a cable system is to be installed directly over and parallel to another underground structure (or

another underground structure installed directly over and parallel to a cable), it may be done providing

all parties are in agreement as to the method. Adequate vertical separation shall be maintained to permit

access to and maintenance of either facility without damage to the other.

D. Thermal Protection

Cable should be installed with sufficient separation from other underground structures, such as steam

or cryogenic lines, to avoid thermal damage to the cable. Where it is not practical to provide adequate

clearance, a suitable thermal barrier shall be placed between the two facilities.

354. Random Separation-Separation Less Than 300 mm (12 in) from Underground

Structures or Other Cables

A. General

1. These rules apply to a radial separation of supply and communication cables or conductors from

each other and from other underground structures when the radial separation between them will

be less than 300 mm (12 in).

1. Radial separation of supply and communications cables or conductors from steam lines, gas, and

other fuel lines shall be not less than 300 mm (12 in) and shall meet Rule

353.

1. Supply circuits operating above 300 V to ground or 600 V between conductors shall be so constructed,

operated, and maintained that when faulted, they shall be promptly de-energized initially

or following subsequent protective device operation (phase-to-ground faults for grounded circuits,

phase-to-phase faults for ungrounded circuits).

1. Communication cables and conductors, and supply cables and conductors buried in random

separation may be treated as one system when considering separation from other underground

structures or facilities.

B. Supply Cables or Conductors

The cables or conductors of a supply circuit and those of another supply circuit may be buried together

at the same depth with no deliberate separation between facilities, provided all parties involved are in

agreement.

C. Communication Cables or Conductors

The cables or conductors of a communication circuit and those of another communication circuit may

be buried together and at the same depth with no deliberate separation between facilities, provided all

parties involved are in agreement.

D. Supply and Communication Cables or Conductors

Supply cables or conductors and communication cables or conductors may be buried together at the

same depth, with no deliberate separation between facilities, provided all parties involved are in

agreement and the applicable rules in 354D1 are met and either Rule 354D2 or

354D3 is met.

EXCEPTION:

Entirely dielectric fiber-optic communication cables may be buried together at the same depth

with no deliberate separation from supply cables or conductors provided all parties involved are in agreement

and Rules 354D1a, b, c, and d are met.

1. General

a. Grounded supply systems shall not be operated in excess of 22 000 V to ground.

b. Ungrounded supply systems shall not be operated in excess of 5300 V phase to phase.

c. Cables of an ungrounded supply system operating above 300 V shall be of effectively grounded

concentric shield construction. Such cables shall be maintained in close proximity to each

other.

d. Ungrounded supply circuits operating above 300 V between conductors and in random

separation with communication conductors shall be equipped with a ground-fault indication

system.

e. Communication cables and communication service wire having metallic conductors or metallic

components shall have a continuous metallic shield under the outer jacket.

EXCEPTION:

This requirement does not apply to Rule 354C.

f. Communications-protective devices shall be adequate for the voltage and currents expected

to be impressed on them in the event of contact with the supply conductors.

g. Adequate bonding shall be provided between the effectively grounded supply conductor or

conductors and the communication cable shield or sheath at intervals that should not exceed

300 m (1000 ft).

h. In the vicinity of supply stations where large ground currents may flow, the effect of these

currents on communication circuits should be evaluated before communication cables are

placed in random separation with supply cables.

1. Grounded Bare or Semiconducting Jacketed Neutral Supply Cables

a. A supply facility operating above 300 V to ground shall include a bare or semiconducting

jacketed grounded conductor in continuous contact with the earth. This conductor, adequate

for the expected magnitude and duration of the fault current that may be imposed, shall be one

of the following:

(1) A sheath, an insulation shield, or both

(2) Multiple concentric conductors closely spaced circumferentially

(3) A separate conductor in contact with the earth and in close proximity to the cable, where

such cable or cables also have a grounded sheath or shield not necessarily in contact with

the earth. The sheath, shield, or both, as well as the separate conductor, shall be adequate

for the expected magnitude and duration of the fault currents that may be imposed.

NOTE:

This is applicable when a cable in nonmetallic duct is considered as a direct-buried cable

installation and random separation is desired.

EXCEPTION:

Where buried cable passes through a short section of conduit such as under a

roadway, the contact with earth of the grounded conductor can be omitted, provided the grounded

conductor is continuous through the conduit.

b. The bare conductor or conductors in contact with the earth shall be of suitable corrosion-resistant

material. The conductor covered by a semiconducting jacket shall be compatible with

the jacketing compound.

NOTE:

Experience has shown that in many geographic areas, bare concentric copper neutral conductors

experience severe corrosion.

c. The radial resistivity of the semiconducting jacket shall be not more than 100

.

m and shall

remain essentially stable in service. The radial resistivity of the jacket material is that value

calculated from measurements on a unit length of cable, of the resistance between the concentric

neutral and a surrounding conducting medium. Radial resistivity is equal to the resistance

of a unit length times the surface area of the jacket divided by the average thickness of the

jacket over the neutral conductors. All dimensions are to be expressed in meters.

1. Insulating Jacketed Grounded Neutral Supply Cables

Each phase conductor of a multi-grounded supply system operating above 300 V to ground and

having an overall insulating jacket shall have an effectively grounded copper concentric conductor

meeting all of the following requirements:

a. A conductance not less than one half that of the phase conductor.

b. A conductance adequate for the expected magnitude and duration of fault current that may be

imposed.

c. A conductance grounded in accordance with Rule 314 except that the grounding interval required

by Rule 96C shall be not less than eight in each 1.6 km (1 mile) of the random buried

section, not including grounds at individual services.

1. Insulating Jacketed Grounded Neutral Supply Cables in Nonmetallic Duct

Insulating jacketed grounded neutral supply cables meeting the rules of

354D3, when installed in

nonmetallic duct, may be random-laid with communication cables.

E. Supply and Communication Cables or Conductors and Non-Metallic Water and Sewer Lines

1. Supply cables and conductors and non-metallic water and sewer lines may be buried together with

no deliberate separation between facilities and at the same depth, provided all parties involved are

in agreement.

1. Communication cables and conductors and non-metallic water and sewer lines may be buried together

with no deliberate separation between facilities and at the same depth, provided all parties

involved are in agreement.

1. Supply cables or conductors, communication cables or conductors, non-metallic water and sewer

lines may be buried together with no deliberate separation between facilities and at the same

depth, provided the applicable rules in Rule 354D are met and all parties involved are in

agreement.

requirement,

section 7.14.1 all cables should be buried to a depth of at least

450 mm with a route marker tape at 150 mm.

sand is a given

Is this the 16th Edition Regs? Thanks

Current UK Regs, Not 16th Edition, but LAW, dictated that all buried cales should have marker tape (or tiles) 150mm above, on top of the sand. This includes provate property, say a small supply at 240 to a shed or fountain would require. Cables in Ducts are different, and do NOT require sand. The duct I believe precludes the marker, but it can still be used.

The law is not retrospective, but any older cables exposed MUST be marked during reinstatement process.

At EHV 132kV and above, you will also find lampost markers and tombstones at boundary crossings.

Hope that helps. You should see what I have had to do in my garden

I have looked on HMSO website at Electricity Supply Regs & Electricity at work regs and cant find any reference to the marking of buried LV cable. Sorry to be persistent, but do you have the reg number? Thanks

16th edition

There is NO requiremnent for utilities to mark LV cable, the 16th Ed does not apply to them and there isn't even a legal depth although you won't have much of a defence if you lay it 2" down and someone is injured. As has been suggested elsewhere in this thread it's good practice if you choose to do it

Jb

You could get Health & Safety involved to confirm your opinion (and most of ours) - they don't even care about Regs

We had a 95mm incoming cut by a JCB - laid by the PoCo so not marked - some tape a good distance above the cable would probably have avoided it.

Incidentaly the cutters (water board) tried to avoid compensation by quoting the PoCo's small print that you are not entitled to an uninterupted supply.

The "wave of the future" in underground wiring seems to be "directional drilling." (I am talking from certain knowledge of Virginia, USA)

A few months ago the utility installed a brand new underground "drop." The length was 440'. The contractor started a few feet away from the transformer pad with a 18" deep trench. The drill machine was guided by a guy with a special sensor and a walkie/talkie to the operator. Basically, he "walked" the drill string from the transformer trench to about 18" from where the conduit to the meter base was. They tied the cable to the drill string and started pulling the new wires (with some mishaps like the wires slipping out, but that's another story.

Basically, there is NO special protection of this cable. No sand, no "warning tape" no nothing.

AND the new run had a failure a month or so after it was installed.

| The "wave of the future" in underground wiring seems to be "directional | drilling." (I am talking from certain knowledge of Virginia, USA) | | A few months ago the utility installed a brand new underground "drop." The | length was 440'. The contractor started a few feet away from the | transformer pad with a 18" deep trench. The drill machine was guided by a | guy with a special sensor and a walkie/talkie to the operator. Basically, | he "walked" the drill string from the transformer trench to about 18" from | where the conduit to the meter base was. They tied the cable to the drill | string and started pulling the new wires (with some mishaps like the wires | slipping out, but that's another story. | | Basically, there is NO special protection of this cable. No sand, no | "warning tape" no nothing. | | AND the new run had a failure a month or so after it was installed.

I watched a crew doing drilling like that once for a gas line. It popped out of the ground on them about 2/3 of the way to the destination, and about 4 meters off to the side. They apparently hit some obstruction that went undetected. So much of the special sensors (though I didn't notice if these guys did anything like that, nor did I see their advance surveys, if they even did any).

I think the guy "walking" the line got a little lazy. In our case, there was one "blowout" when the drilling mud came up to the surface. They just backed off a few feet and changed the heading.

(For the curious: the drilling bit has a slant so it wants to go off in one direction. To go staight, they just rotate the string while pumping mud and pushing the string.)

A few years ago I watched a crew put a telephone cable under a paved street. They had a similar drilling rig except there was to mud and no direction control. To "catch" the string on the other side of the road they ended up with a 10' deep trench. I stopped watching because I didn't want to take a chance of being a witness to a man being buried alive.

>