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1 Introduction

Incidents involving damage to electricity supply lines can have serious consequences for workers and adversely impact on the community. Various types of works have the potential to cause such damage but adequate precautions can dramatically reduce the risk of an incident. This Code outlines the dangers and provides advice on how to reduce risk.

1.1 Background
1.2 Scope
1.3 Definitions
1.4 The dangers associated with damage to U/G cables and O/H lines
1.5 Electricity supply in Hong Kong

1.1 Background

1.1.1 Damage to electricity supply lines can cause electrical accidents¹ and electricity supply interruptions. Fatal accidents and serious injuries have occurred during excavation close to underground electricity cables and during lifting operations by cranes or hoists near overhead electricity lines. In addition, damage may also cause an electricity supply interruption that could potentially affect thousands of homes and businesses.

1.1.2 This Code outlines the dangers that can arise from works near underground electricity cables ("U/G cables") or overhead electricity lines ("O/H lines") and gives guidance on how to reduce the risk. It deals specifically with risks to persons carrying out works and the necessary precautions needed to reduce the risk of accidents due to damage and unsafe practices.

1.1.3 During the preparation of this Code, the Director of Electrical and Mechanical Services ("the Director") consulted the electricity suppliers, the construction industry, the other utility companies and relevant Government Departments. The views and advice given by these organizations have been taken into account in this Code wherever possible.

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1.2 Scope

1.2.1 This Code applies to all works carried out in the works site or in its vicinity where U/G cables or O/H lines may be found. In addition to a safe system of work, it provides practical safety precautions to avoid damage to electricity supply lines in different situations, including works that involve excavation, ground penetration, lifting operations by cranes or hoists, and earth moving operations by heavy machinery.

1.2.2 The term "works" is defined in the ESLPR and this definition is also included under Section 1.3.1.7 of this Code. However, the following works need not follow the safe system of work set out in this Code unless probable damage to U/G cables is seen:

(a) the milling of paved surface up to 120mm below ground level in carriageways for the purpose of road resurfacing; and

(b) the replacement of existing paving block up to 120mm below ground level.

Moreover, this Code does not apply to dredging works and extraction of material from the seabed.

1.2.3 This Code is intended to be used by all those who have responsibilities under relevant legislation, including employers, employees, contractors², competent persons, electricity suppliers and those concerned with planning, designing, organizing and supervising works near U/G cables or O/H lines. Those who wish to carry out their works in some other ways than that provided in this Code must ensure that they achieve an equal or higher standard of safety.

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1.3 Definitions

1.3.1 This Code adopts the following definitions from the Electricity Ordinance ("EO") or ESLPR:

1.3.1.1 "competent person" means a person approved as a competent person³ under Section 3 (of ESLPR).

1.3.1.2 "electricity supplier" means a person who generates, supplies and sells electricity at low or high voltage for use in an electrical installation.

1.3.1.3 "electricity supply line" means an electric line or any cable used in conjunction with such a line for the purpose of transmitting control signals, which is owned by an electricity supplier.

1.3.1.4 "overhead electricity line" (O/H line) means an electricity supply line located at or above ground level.

1.3.1.5 "site contractor" means a person who carries out or is engaged to carry out any works on a particular works site.

1.3.1.6 "underground electricity cable" (U/G cable) means an electricity supply line located below ground level.

1.3.1.7 "works" means -

(a) any kind of works involving or in connection with –

(i) building works⁴ within the meaning assigned to that term in Section 2(1) of the Buildings Ordinance (Cap.123), and for the purposes of this subparagraph reference in that Section to "ground investigation in the scheduled areas" shall be read as a reference to "ground investigation";

(ii) the laying out, construction, alteration or repair of any road (whether or not at ground level), footpath, cycle track, pedestrian subway, footbridge, tunnel, airport runway, canal, reservoir, pipeline, railway or tramway;

(iii) trench works, including -

(A) water mains, storm water drains and sewers; and
(B) such works when carried out by or for any public utility;

(iv) the extraction of material from land or the seabed;

(v) landfill works, river training works, slope works or reclamation works; or

(vi) levelling, piling, ramming, dredging, boring, tunnelling or blasting works;

(b) the use of any crane or hoist (within the meaning assigned to those terms in Regulation 2(1) of the Construction Sites (Safety) Regulations (Cap.59 sub.leg.)) or other equipment for the purpose of lifting objects;

(c) the use of any heavy machinery or other equipment for the purpose of earth moving.

but does not include works necessary to ascertain the alignment and depth of an underground electricity cable, nor any electrical work carried out by a registered electrical worker or registered electrical contractor.

1.3.1.8 "works site" means any area in which works are being carried out.

1.3.2 The following terminologies are used in this Code:

1.3.2.1 "hand tool" means a non-mechanized tool designed for operation by hand including, but is not limited to spades, shovels, picks or forks.

1.3.2.2 "hand-held power tool" means a hand-held mechanized tool designed for operation that utilizes electrical or pneumatic power.

1.3.2.3 "minor shallow excavation" means an excavation limited to 2 sq. m x 450mm in depth and dug using hand tools with the exception that hand-held power tools can be used to break the paved surface up to a depth of 150mm in a footpath or 450mm in a carriageway and, in both cases, with at least 250mm clearance from any cable alignment.

1.3.2.4 "trial hole" means an excavation for exposing part of the target cable, carried out under the supervision of a competent person at the point of works where the working personnel use hand tools for digging with the exception that hand-held power tools can be used to break the paved surface up to a depth of 150mm in a footpath or 600mm in a carriageway and, in both cases, with at least 250mm clearance from any cable alignment.

1.3.2.5 "works in the vicinity of U/G cables" are defined in Table 1.

Table 1 - Works below ground level in the vicinity of U/G cables

1.3.2.6 "works in the vicinity of overhead lines" means any works, except for blasting works, found within a horizontal distance of 9m from the outermost conductor of an O/H line (Fig 1). For blasting works, they are considered as works in the vicinity of O/H lines if any blasting point is within a horizontal distance of 25m from the nearest O/H conductor or radial distance of 50m from the centre of any O/H line footing.

Fig 1 – Works in the vicinity of overhead lines (except blasting works)

1.3.2.7 "working party" means any person, including contractor, site contractor and site personnel, concerned with planning, designing, organizing and supervising works near U/G cables or O/H lines.

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1.4 The dangers associated with damage to U/G cables and O/H lines

1.4.1 Damage to U/G cables can cause fatalities or severe injuries and electricity supply interruptions. There are three common types of damage to U/G cables:

(a) Damage due to penetration by a sharp object up to the cable conductor. This will immediately cause an explosive arcing current and a short-circuit fault on the U/G cable.

(b) Damage due to penetration by a sharp object up to the cable insulation. While this may not cause immediate danger, it constitutes a potential hazard and could result in an electrical fault later as the damaged insulation deteriorates.

(c) Damage due to mechanical stress in the U/G cable. Mechanical stress often occurs when a long section of U/G cable is overhanging without proper support or when the earthworks fall onto an exposed U/G cable. This stress is transmitted to the nearest cable joint, where an electrical fault may subsequently develop.

1.4.2 Damage to the control cables associated with U/G cables could trip major cable circuits and cause electricity supply interruptions.

1.4.3 Other services, such as plastic gas pipes, may also be at risk if they are near to damaged live U/G cables. If the gas main leaks at the same time, the damage could cause a gas explosion which imposes a higher risk to the persons in the surrounding.

1.4.4 Getting close to O/H lines, or coming into contact with them, is highly dangerous and may result in fatalities, severe injuries, shocks or burns to any persons in the vicinity due to an electrical explosion or arcing from the O/H lines. The instantaneous short circuiting of high voltage O/H lines to the ground, following damage or interference by an overhead crane, can cause a voltage surge on the ground potential. Any persons on the ground in the

vicinity may suffer electric shock, and any electrical products in nearby houses may burn out.

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1.5 Electricity supply in Hong Kong

1.5.1 Electricity supply lines used for the transmission and distribution of electricity are scattered throughout Hong Kong Island, the Outlying Islands, Kowloon and the New Territories. Currently there are two electricity suppliers in Hong Kong, namely, CLP Power Hong Kong Ltd. (CLP) and The Hongkong Electric Co. Ltd. (HEC). Both CLP and HEC own and operate extensive electricity supply systems at various voltage levels. Consumers in Hong Kong Island, Lamma Island and Apleichau are supplied by HEC while CLP supplies electricity to consumers in the rest of Hong Kong Special Administrative Region ("HKSAR"). The electricity supply systems operated by CLP and HEC are outlined in Appendix 3. The typical colours, sizes and buried depths of CLP's and HEC's U/G cables are given in Table 2 of Appendix 3.

Demarcation of electricity supply systems between CLP and HEC

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¹ Electrical accident means an incident involving electricity that causes a fire or explosion or that causes death or injury to a person (Section 2 of Electricity Ordinance). [Go Back]

² Contractor, in relation to works, means any person or site personnel engaged in carrying out works by way of trade or business, either on his own account or pursuant to a contract or arrangement entered into with another person including the Government or any public body. [Go back]

³ Under Section 6 of ESLPR, a person's approval as a competent person may be suspended or revoked by the Director in accordance with subsection (1) or (2) respectively. [Go Back]

⁴ It should be noted that "building works" includes any kind of building construction, site formation works, ground investigation in the scheduled areas as defined in the Building Ordinance (Cap.123), foundation works, repairs, demolition, alteration, addition and every kind of building operation, and includes drainage works.[Go Back]

⁵ Measurement is taken from the centre line of the U/G cable to determine whether works will be considered to be in its vicinity. [Go Back]

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