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This guide can be downloaded as a PDF from the Hager website - the Hager Guide to Commercial Installations. The whole nature of electrical sub and final distribution for commercial installations has changed in the last few years. There is a demand for more RCD protection of final circuits, more metering and often more control to meet energy saving targets.
This guide expands upon some of the requirements found in the 17th Edition of the IEE Wiring Regulations and Building Regulations and how they affect Type B MCB distribution boards and their protective devices.
You should be aware that this guide does not ensure compliance with BS 7671 or the Building Regulations. You should always consult the relevant regulations to ensure compliance.
The Hager Type A & B distribution boards
Manufacturers refer to Type A or Type B distribution boards. This terminology refers to the busbar arrangement and the type of overcurrent protective device (OCPD) that it accepts.
- Type A distribution boards have a busbar arrangement designed to accept single and/or double pole OCPDs. They typically have a horizontal busbar arrangement that accepts multi-pole and/or single pole OCPDs.
- Type B distribution boards have a busbar arrangement designed to accept multi-pole and/or single pole OCPDs. They generally have a vertical busbar with the OCPDs connected to the sides.
The Selection & erection
All equipment must be correctly selected and erected. BS 7671 states that the following, along with manufacturer’s instructions should be considered:- Compliance with standards;
- Operational conditions;
- External influences;
- Accessibility.
The Hager Commercial Distribution Boards - Compliance with standards
A fundamental principle of BS 7671 is that all equipment must comply with the appropriate British Standard. For distribution boards BS EN 60439-3 is applicable.If equipment has a foreign standard based on an IEC standard then the designer or specifier must confirm that any differences will not result in reduced safety.
The Hager Commercial Distribution Boards - Operational conditions
The electrical designer will need to select distribution boards for operational conditions such as voltage, current and frequency. In the UK the nominal voltage and frequency is typically 400/230V and 50Hz.Installations and the distribution boards within them will, however, have different current requirements. 512.1.2 in the 17th Edition requires that the equipment is suitable for the design current and the current likely to flow in abnormal conditions.
The latter would include short circuit and earth faults. The specifier will therefore need to assess the current demand taking into account diversity.
They will also need to assess the prospective fault current at the distribution board location before selecting the board and the protective devices.
The Hager Distribution Boards - External influences
All equipment including the distribution board must be suitable for the external influences that they are likely to encounter. There will be conditions where a suitably IP rated distribution board will be needed. These installations may include:
- Caravan parks;
- Marinas;
- Agricultural or horticultural installations;
- Temporary electrical installations for structures at fairgrounds, amusement parks and circuses;
- Locations where there is a risk of fire due to the nature of processed or stored materials.
