Hager - Benefits of Pre-Fabricated Wiring Systems

Benefits of Pre-Fabricated Wiring Systems - Standard Specification BS 7671 BS 8488 Conformity

Introduction

Specifiers and installers have, for a number of years, been keen to exploit the benefits of prefabricated wiring systems as an alternative to conventional fixed wiring methods.

Prefabricated wiring systems can be used in suspended floors and ceilings, which are commonly used in buildings or structures. By using prefabricated wiring systems, the installation work becomes quicker than using traditional methods as they are designed to provide rapid connection which guarantees the correct connection. An example is where separate luminaires can be easily linked to form a comprehensive lighting system by using a prefabricated wiring system (see diagram below).

Comprehensive lighting system using a prefabricated wiring system

Does it comply with the appropriate safety requirements,
as a complete system?

Some prefabricated wiring systems have been associated with serious safety issues: reversed polarity, under rated couplers and incorrectly sized wiring sections have been areas of concern.

The Need for a System Safety Standard

The absence of a system standard that specified safety requirements, together with associated testing, led to a new British Standard BS 8488:2009+A1:2010 Prefabricated wiring systems intended for permanent connection in fixed installations, being issued.

System Safety Standard Specification

BS 7671 recognises equipment complying with an appropriate British Standard or Harmonised Standard without further qualification. This approach means that the person responsible for specifying the prefabricated wiring system must, identify the “appropriate” standard.

BS 8488 specifies safety requirements, together with associated tests, for prefabricated wiring systems incorporating installation couplers conforming to BS EN 61535.

Some key safety requirements and tests prescribed in BS 8488 are:

• Protection against electric shock
• Insulation resistance and electric strength
• Clearances and creepage distances
• Resistance to heat, fire and tracking
• Routine tests (during and/or after manufacture)

System Design to BS 7671

BS 8488 requires the following details to be provided with each prefabricated wiring section, if they are necessary to ensure safe use and maintenance:

• Instructions for safe use
• System design information, validating conformity with BS 7671
• Information required to facilitate inspection and testing for conformity with BS 7671

BS 8488 identifies the need for system design, installation & verification for conformity with BS 7671. Some design elements of the system that need to be verified for conformity with BS 7671 are:

Design Current

The design current for discharge lighting must take into account control gear losses and harmonic current.

Overcurrent Protective Devices

The characteristics of the overcurrent protective device must take into account inrush and starting currents e.g. those associated with transformers and discharge lighting.

Cross-sectional Area of Live Conductors

BS 8488 prescribes that the rated current shall be assigned according to a reference method defined by the manufacturer from BS 7671:2008, Table 4A2. This needs to be distinctly and durably marked on each individual section.

The rated current and cross-sectional area of the wiring section conductors shall be determined on the following basis:

• The number of loaded cores defined by the manufacturer. A loaded core is where the conductor carries more than 30% of its rating, after applying the rating factor for the total number of current carrying cores;
• Not being grouped with other wiring systems or cables;
• Not being in contact with thermal insulation;
• The ambient temperature not exceeding 30°C;
• The frequency of operating being not greater than 61 Hz.

BS 8488 states that the required current-carrying capacity of a system section should be determined by the system designer by applying rating factors for the specific installation conditions. This current carrying capacity may be different from the rated current.

Competency to Certify Conformity with BS 8488

One aspect that must not be overlooked by the person responsible for specifying the prefabricated wiring system is ensure that all products have been tested and a declaration of conformity issued by an independently recognised laboratory.

To ensure that all of the above requirements are achieved Hager has developed klik.system, bringing together a full range of connectors, a bespoke design software system, tailor made logistics, full commissioning and support package.