Hager Commercial Distribution Boards - Cable entryDesigners 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.
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 alternativeAnother 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 switchingIsolation 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 5220.127.116.11 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 518.104.22.168, 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.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.]