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Gangway requirements
from Connections - Summer 2012
by NICEIC
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Operating and Maintenance Gangways are one of a number of new special installations or locations added to Part 7 of BS 7671: 2008 by Amendment No 1, which came into eff ect on 1 January. An operating and maintenance gangway is defined in BS 7671 as a gangway that provides access to facilitate operations such as switching, controlling, setting, observation and maintenance of electrical equipment.
As for all the special installations and locations in Part 7 of BS 7671, the requirements of Section 729, Operating and Maintenance Gangways, supplement or modify the general requirements of BS 7671.
The requirements of Section 729 apply to basic protection and other safety aspects, including those for operating or maintenance gangways, in areas containing switchgear and controlgear assemblies where access to the area is restricted to skilled persons or instructed persons under the supervision of a skilled person.
The requirements of Section 729 do not apply to situations where switchgear or controlgear are installed in a location where access is rightly not restricted to skilled or instructed persons. This could be the case, for example, where protection against electric shock for all equipment in the location relies on the generally permitted protective measures listed in Regulation 410.3.3, such as automatic disconnection of supply, and not on obstacles or placing out of reach (Section 418). However, the general requirements of BS 7671 still apply in such situations, such as the requirements of Chapter 41 for protection against electric shock and Regulation 132.12 for accessibility.
Control of access to the special location
The areas restricted to skilled or instructed persons must be clearly marked by means of appropriate signage (see Fig 1), and measures must be taken to prevent unauthorised access (Regulation 729.3 refers).
The latter requirement will most likely be met by securing the access doors by conventional lock and key, or perhaps by security card reader or similar. However, evacuation from the location should be unrestricted and not require the use of a key or tool or anything other than the opening mechanism. Fig 1 Example of
signage to mark restricted access areas
Gangway width and headroom
Two fundamental requirements, given in Regulation Group 729.513.2, are that: • the width of gangways and access areas must be adequate for work, operational access, emergency evacuation, and transport of equipment, and • gangways must permit at least 90° opening of equipment doors or hinged panels.
Subject to the above requirements, the minimum width and headroom dimensions for gangways are given in Regulation 729.513.2.1 where basic protection against electric shock is provided by barriers or enclosures in accordance with Section 416, and in Regulation 729.513.2.2 where basic protection is provided by obstacles in accordance with Section 417. The minimum dimensions are summarised in Table 1 of this article.
It is interesting to note that the minimum height of 2500 mm for placing bare live parts out of reach (see Table 1, bottom row) exceeds the fi gure of 7 feet (2.1336 m) for the minimum height to a bare live low voltage conductor that applied in regulation 17 of the Electricity (Factories Act) Special Regulations 1908 & 1944, which appears as a historical comment in Appendix 3 of the Memorandum of guidance on the Electricity at Work Regulations 1989 (HSR25).
The gangway width and headroom dimensions given in Section 729 (and summarised in this article) are absolute minima. Larger clearances must be provided where circumstances dictate this.
The Health and Safety Executive (HSE) has reported fi nding in the past that, even with fully enclosed switchgear and controlgear conforming to relevant standards, inadequate space has been provided between, for example, the front of a switchboard and a facing wall, which has prevented operating handles from being fully extended. Equally, the HSE has also found cases where switchboards have been erected face to face with inadequate spacing to allow safe operation, and that withdrawable units have been installed with insuffi cient space to withdraw and work on them.
It is essential that suffi cient working space is provided in all situations.
Access to gangways and for evacuation in emergency
The requirements for access to gangways and for evacuation in an emergency are given in Regulation 729.513.2.3 and Annex A729.
The fundamental requirements for access are that gangways exceeding 10 m in length are to be accessible from both ends, and that closed restricted access areas with a length exceeding 20 m are to be accessible by doors at both ends (Regulation 729.513.2.3 refers). However, a note to Regulation 729.513.2.3 recommends accessibility from both ends of a closed restricted access area if the length exceeds 6 m. Examples of the positioning of doors in various
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Table 1 Gangway minimum width and height above
Gangway characteristic
Gangway width including between: • barriers or enclosures (or obstacles, where applicable) and switch handles in their most onerous position, and • barriers or enclosures (or obstacles, where applicable) or switch handles in their most onerous position and the wall Gangway width between barriers or enclosures (or obstacles, where applicable) and other barriers or enclosures (or obstacles, where applicable) and the wall Height of barrier or enclosure (or obstacle, where applicable), measured from gangway floor Height of Iive parts placed out of reach (Regulation 417.3), measured from gangway floor
Minimum applicable dimension (mm)
700 (see Fig 2)
700 (see Fig 2)
2000
2500
Notes.
1) This table gives only a summary of the relevant requirements.
For the full requirements, see BS 7671, Section 729. 2) Larger dimensions may be required for particular items of switchgear or controlgear (including for transport of these). 3) See Fig 3 regarding provision of space to permit 90° opening of equipment access doors or hinged panels. 4) The use of obstacles is permitted only for parts of the installation that are controlled or supervised by skilled persons (Regulations 417.1 and 729.513.2.2 refer). Obstacles are therefore unsuitable for use where an instructed person not under the supervision of a skilled person is authorised to access an area.
situations are given in Fig 729.3 of the regulation.
The main evacuation requirements in Annex A729 can be summarised as: • doors of equipment must close in the direction of the evacuation route • gangways must permit at least 90° opening of equipment access doors or hinged panels • doors that can be fi xed in the open position and circuit-breakers that are fully withdrawn for maintenance require at least 500 mm clearance to the opposite limitation of the gangway when the door is open or the circuit-breakers fully withdrawn (see Fig 3).
Where items of switchgear or controlgear are installed face to face, it is important that if equipment doors need to be opened, or circuit-breakers need to be withdrawn, opposite each other, at least the minimum passing width shown in Fig 3 is available with doors fully open/circuitbreakers fully withdrawn. Fig 2 Minimum width of gangway
(to be read with Table 1)
Fig 3 Minimum passing width (for evacuation) allowing for 90° opening of access doors and withdrawal of circuit-breakers
Barriers or enclosures
Circuit-breaker in the position “isolation”
700 mm
Elevation view
700 mm
Plan view
Minimum passing width 500 mm*
1 2
1
Fixing device of a door
*The minimum width of a gangway of 500 mm shall be taken into consideration between the wall and the circuit-breaker in the position “completely extracted” and equipment door in the 90 degree position
