Is there any requirements for the laying of underground cables (600/1000V
SWA), for them to be laid on a bed of sand within a cable trench.
Also, is it at requirement that underground cables need to be marked with
cable marking tape or slabs laid above the cable in the trench, before
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...
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)
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.
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
D. Cables of the same circuit operating below 600 V to ground and without an
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
(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.
Cables with jackets that cannot be effectively marked in accordance with
Rule 350G need not
Unmarked cable from stock existing prior to 1 January 1996 may be used to
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
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.
2. 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
3. Cable systems should be routed so as to allow safe access for
construction, inspection, and
4. 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
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
2. 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.
3. 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.
Where this is impractical, or for other reasons, this clearance may be
reduced by agreement
between the parties concerned.
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
4. 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.
5. 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
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.
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.
2. 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
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
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
2. 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
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.
Supply Cable or Conductor Burial Depth
(See Rule 352D)
Depth of burial
0 to 600 600 24
601 to 50 000 750 30
50 001 and above 1070 42
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
Structures or Other
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
For radial separation less than 300 mm (12 in) see Rule 354.
2. The radial separation should be adequate to permit access to and
maintenance of either facility to
limit damage to the other.
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
2. 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.
3. 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
354. Random Separation-Separation Less Than 300 mm (12 in) from Underground
Structures or Other Cables
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).
2. 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
3. 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
or following subsequent protective device operation (phase-to-ground faults
for grounded circuits,
phase-to-phase faults for ungrounded circuits).
4. Communication cables and conductors, and supply cables and conductors
buried in random
separation may be treated as one system when considering separation from
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
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.
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.
a. Grounded supply systems shall not be operated in excess of 22 000 V to
b. Ungrounded supply systems shall not be operated in excess of 5300 V phase
c. Cables of an ungrounded supply system operating above 300 V shall be of
concentric shield construction. Such cables shall be maintained in close
proximity to each
d. Ungrounded supply circuits operating above 300 V between conductors and
separation with communication conductors shall be equipped with a
e. Communication cables and communication service wire having metallic
conductors or metallic
components shall have a continuous metallic shield under the outer jacket.
This requirement does not apply to Rule 354C.
f. Communications-protective devices shall be adequate for the voltage and
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
placed in random separation with supply cables.
2. Grounded Bare or Semiconducting Jacketed Neutral Supply Cables
a. A supply facility operating above 300 V to ground shall include a bare or
jacketed grounded conductor in continuous contact with the earth. This
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
This is applicable when a cable in nonmetallic duct is considered as a
installation and random separation is desired.
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
material. The conductor covered by a semiconducting jacket shall be
the jacketing compound.
Experience has shown that in many geographic areas, bare concentric copper
experience severe corrosion.
c. The radial resistivity of the semiconducting jacket shall be not more
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
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
3. 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
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
section, not including grounds at individual services.
4. 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
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
2. 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.
3. 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
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
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?
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
The LV cable installation has been done on one of our sites as a supply to a
distribution board. It is not a supply from the REC.
The cable has not been marked, and buried direct in a trench where there are
quite a lot of stones.
The installation was overseen by one of our (know-it-all) engineers - AN ICA
ENGINEER. The cable was installed by contractors that happen to be his
He has been quick in the past to put down other peoples installations and in
the end he has been proven wrong.
I say that this installation is unacceptable and in breach of regulations. I
need some ammo and be sure I am right before I go shouting my mouth off.
So all the help I can get would be appreciated.
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
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.