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Hager Guide to Commercial Installations(2), the cable entry + the isolation and switching

  2010-12-08         admin         Advice » Consumer Units Advice,   Installation Guides
After introducing the Type B Distribution Boards and compliance with standards in the first part of the Hager Distribution Boards guide, in this article we're presenting the Cable Entry and the Isolation and Switching of the Hager Boards. Download the entire guide from the Hager website - Hager Guide to Commercial Installations.

Hager Commercial Distribution Boards - Cable entry

Designers and installers must select a wiring system that avoids damage to the sheath and insulation of cable during installation, use and maintenance. Where cables enter a distribution board from trunking, the cables must be protected from any sharp edges in order to comply with 522.8.1. Common methods of complying include deburring edges and using grommet strips or manufactured spacers.

Regulation 526.9 requires that the cores of unsheathed cables from which the sheath has been removed and non-sheathed cables at the termination of the trunking etc are enclosed. Complying with these regulations can be difficult when passing the cables from the trunking into a distribution board. The on-site construction of a spacer using material such as paxolin is a common solution. This is, however, time consuming and produces dust, so appropriate health and safety protection may need providing. Also the installer must take care that the solution fully complies with the regulations by making a proper seal.
Not only does this cable entry system meet the requirements of the regulations, but it also cuts the time taken to fit the board to trunking by up to four times.

Hager Commercial Distribution Boards - A better alternative

Another answer is to use a distribution board that has an end plate adapted for coupling to trunking. In Hager’s new boards, for example, the end plate has a removable section that leaves a smooth edge return that is free from screw heads and nuts. This allows flush coupling to trunking and a smooth entry for cables to meet the requirements of 522.8.1 and 526.9 of the Wiring Regulations. Not only does this cable entry system meet the requirements of the regulations, but it also cuts the time taken to fit the board to trunking by up to four times.

In an independent trial, the time taken to fit a typical distribution board to trunking when the installer needs to cut out the gland plate and cut paxolin to shape was 50 minutes. When there is no need to prepare gland plates, use paxolin or adjust the trunking, the same installer took just 13 minutes to fit the comparable Hager board.

Hager Commercial Distribution Boards - Isolation and switching

Isolation aims to make dead, for safety reasons, all or a discrete section of the electrical installation by separating it from every source of electric energy. This is commonly achieved by switching off an isolation device within the distribution board. Regulation 537.2.2.1 requires that the device shall isolate all live conductors, subject to the provisions of regulation 537.1.2. The neutral conductor is also a live conductor. In a TN-S or TN-C-S installation, however, regulation 537.1.2 allows the neutral conductor to not be isolated where it is reliably connected to earth. If the supply complies with the Electrical Safety, Quality and Continuity Regulations 2002, a three-pole isolating device is sufficient for a three-phase supply. Regulation 537.2.1.7, however, says that there should be some provision for disconnecting the neutral, for example by using a bolted link. Three-phase TT supplies will require disconnection of the neutral, so a four-pole isolation device is needed. For a single-phase supply where the main switch will be used by ‘ordinary persons’, the isolating switch must interrupt both live conductors.

The below Table 53.2 identifies that circuit breakers to BS EN 60947-2 are suitable for isolation. These are commonly used as outgoing devices in distribution boards and can be used as isolation devices for individual circuits. The table below gives guidance as to whether the neutral conductor needs to be switched or not.

BS 7671 also requires that the device used for isolation is designed and/or installed so as to prevent unintentional or inadvertent closure. Usually this means that you need to fit some kind of locking mechanism to the device. IEE Guidance Note 2 gives more detailed guidance on isolation and switching.

[This is the second part of the full Hager Guide to the Commercial Installations, dealing with the cable entry and the isolation&switching of the Hager Distribution Boards(download the full pdf file of the guide via the Hager website). Read the first part online via the Hager Guide to Commercial Installations(1), Type B Distribution Boards and compliance with standards, or continue reading our blog for the next parts.]