GROUNDING

Cable support systems by PARTNER have been tested and certified for compliance with the requirements of the following regulatory documents:

• GOST R 52868-2007, para. 11.1
• Electrical Installations Code, 7th edition, para. 1.7.90
• Electrical Installations Code, 7th edition, para. 1.7.139

and may be used as a protective PE-conductor (connection points of cable tray and cable ladder system components ensure electric circuit continuity).

Main documents determining the mandatory rules when using metal cable trays as passive protection or earthing conductor are:

• Electrical Installations Code (EIC, 7th edition, Chapter 1.7 Earthing and Electric Safety Protective Measures.
• Rules of Technical Operation of Electric Installations of Consumers (RTO of Electric Installations of Consumers, Section 2 General Purpose Electrical Equipment and Electrical Installations, Chapter 2.7. Earthing Arrangements).
• GOST R 50571.5.54-2013/ IEC 60364-5-54:2011. Earthing Arrangements, Protective Conductors and Protective Bonding Conductors.

In addition to these mandatory documents, there are technical specifications and certificates of conformity, technical data sheets issued by metal cable tray manufacturers. They contain descriptions, technical parameters of products and specify their scope of application.

Basic Requirements for Earthing of Cable Support Structures

To improve safety of electrical installations, a number of measures shall be implemented. One of such measures is earthing. “Requirements for protection in case of indirect contact apply to: 4)… cable trays, trunks, hangers, strings and bars where cables and wires are routed (except for hangers, strings and bars used for routing cables with bonded or grounded metal sheathing or armor), as well as other metal structures where electrical equipment is installed…” (EIC, para. 1.7.76)

Potential for application: “Metal cable trunks and trays for electric wiring may be used as protective conductors provided that cable trunk and tray structure allows for such application, and the manufacturer’s documentation contains an express indication to that effect, and their location eliminates any probability of mechanical damage…” (EIC, para. 1.7.121)

Arrangement of metal cable trunk earthing, as well as their use as an earthing conductor, shall be allowed only in compliance with the electrical installation design. The design must consider the parameters of cable trays and their characteristics specified by the manufacturer: “Cable trunk and tray structure allows for their use as earthing (protective) conductors, and the manufacturer’s documentation contains an express indication to that effect, and their location eliminates any probability of mechanical damage” (EIC, para. 1.7.121). Typically, metal sections have galvanic connection in addition to mechanical one. It is made either as a conductive plate connecting two cable trays, or a conductor with two terminals.

In both cases, a screw connection is used which is allowed for earthing, neutral grounding or bonding circuits installed indoors in rooms with non-corrosive environment or in outdoor electrical installations. In this case, the requirements of GOST 10434 “Electric Contact Connections. General Technical Requirements” for connections of class 2 shall be met. (EIC, para. 1.7.139; 1.7.142)

Some limitations are established for metal cable tray use as an earthing conductor:

• Protection against mechanical, chemical and electrochemical damage shall provide electric circuit continuity along the entire cable tray length.
• According to their conductive properties, electric circuit of cable trays is as good as a grounding system. It is achieved by selecting an earthing conductor cross section area, or by calculations according to EIC, para. 1.7.126. For that purpose, the short-circuit current value and selectivity time of switching device disconnecting the required wiring section are used.
• Provisions shall be made for possible connection of other protective conductors in the specified points (GOST R 50571.5.54-2013, Section 543 Protective Conductors).

Conditions for Cable Tray Use as Earthing Conductors.

When planning to use cable support systems as earthing conductor, it is necessary to remember the following:

• dedicated conductors shall be used (cores of multi-core cables; insulated or non-insulated conductors in common sheathing with phase conductors; fixed installed insulated or non-insulated conductors);
• secondarily, exposed conductive parts of electrical installations (aluminum sheathing of cables; steel pipes of electric wiring; metal sheathing and support structures of bus ducts and prefabricated modular package units).
• only if all the above options are unavailable, metal cable trunks and trays for electric wiring shall be used (EIC, para. 1.7.121; 1.7.122).

To use cable support systems as earthing conductor when no method statement for the works is provided, reference materials or cable support system manufacturer’s documents shall be used, electrical resistivity of products shall be determined or measured by means of an electrotechnical laboratory (measurement procedure as per GOST 17441-84 for determination of an earthing conductor resistance). Short-circuit currents shall be calculated (for that purpose, we recommend to use the regulation RD 153-34.0-20.527-98 Guidelines for Calculation of Short Circuit Currents and Selection of Electrical Equipment) to determine dynamic and thermal withstand capability of a cable support system. Then, a minimum cross section area of an earthing conductor shall be determined based on the above calculation. The obtained value shall be compared with the cross section area of the selected metal cable tray (typically, the cross section area value is provided by the manufacturer).

Requirements for Cable Tray Resistance.

Resistance of cable tray sections and elements is determined by GOST R 52868-2007 (IEC 61537:2006). It states that impedance values shall be maximum 50 MΩ for connections between sections and 5 MΩ per running meter for entire section length.