Quality and safety of an electrical installation
From Electrical Installation Guide
In so far as control procedures are respected, quality and safety will be assured only if:
- The initial checking of conformity of the electrical installation with the standard and regulation has been achieved
- The periodic checking of the installation recommended by the equipment manufacturer is respected.
- The electrical equipment comply with standards
Initial testing of an installation
Before a utility will connect an installation to its supply network, strict pre-commissioning electrical tests and visual inspections by the authority, or by its appointed agent, must be satisfied.
These tests are made according to local (governmental and/or institutional) regulations, which may differ slightly from one country to another. The principles of all such regulations however, are common, and are based on the observance of rigorous safety rules in the design and realization of the installation.
IEC 60364-6-61 and related standards included in this guide are based on an international consensus for such tests, intended to cover all the safety measures and approved installation practices normally required for residential, commercial and (the majority of) industrial buildings. Many industries however have additional regulations related to a particular product (petroleum, coal, natural gas, etc.). Such additional requirements are beyond the scope of this guide.
The pre-commissioning electrical tests and visual-inspection checks for installations in buildings include, typically, all of the following:
- Insulation tests of all cable and wiring conductors of the fixed installation, between phases and between phases and earth
- Continuity and conductivity tests of protective, equipotential and earth-bonding conductors
- Resistance tests of earthing electrodes with respect to remote earth
- Verification of the proper operation of the interlocks, if any
- Check of allowable number of socket-outlets per circuit
- Cross-sectional-area check of all conductors for adequacy at the short-circuit levels prevailing, taking account of the associated protective devices, materials and installation conditions (in air, conduit, etc.)
- Verification that all exposed- and extraneous metallic parts are properly earthed (where appropriate)
- Check of clearance distances in bathrooms, etc.
These tests and checks are basic (but not exhaustive) to the majority of installations, while numerous other tests and rules are included in the regulations to cover particular cases, for example: TN-, TT- or IT-earthed installations, installations based on class 2 insulation, SELV circuits, and special locations, etc.
The aim of this guide is to draw attention to the particular features of different types of installation, and to indicate the essential rules to be observed in order to achieve a satisfactory level of quality, which will ensure safe and trouble-free performance. The methods recommended in this guide, modified if necessary to comply with any possible variation imposed by a utility, are intended to satisfy all precommissioning test and inspection requirements.
Periodic check-testing of an installation
In many countries, all industrial and commercial-building installations, together with installations in buildings used for public gatherings, must be re-tested periodically by authorized agents.
Figure A3 shows the frequency of testing commonly prescribed according to the kind of installation concerned.
|Type of installation||Testing Frequency|
| Installations which|
require the protection
|| Annually |
|Other cases||Every 3 Years|
| Installations in buildings|
used for public gatherings,
where protection against
the risks of fire and panic
| According to the type of establishment and its capacity for receiving the public || From one to |
|Residential||According to local regulation|
Fig A3: Frequency of check-tests commonly recommended for an electrical installation
Conformity (with standards and specifications) of equipment used in the installation
|Conformity of equipment with the relevant standards can be attested in several ways|
Attestation of conformity
The conformity of equipment with the relevant standards can be attested:
- By an official mark of conformity granted by the certification body concerned, or
- By a certificate of conformity issued by a certification body, or
- By a declaration of conformity from the manufacturer
- The first two solutions are generally not available for high voltage equipment.
Declaration of conformity
Where the equipment is to be used by skilled or instructed persons, the manufacturer’s declaration of conformity (included in the technical documentation), is generally recognized as a valid attestation. Where the competence of the manufacturer is in doubt, a certificate of conformity can reinforce the manufacturer’s declaration.
Note: CE marking
In Europe, the European directives require the manufacturer or his authorized representative to affix the CE marking on his own responsibility. It means that:
- The product meets the legal requirements
- It is presumed to be marketable in Europe
The CE marking is neither a mark of origin nor a mark of conformity.
Mark of conformity
Marks of conformity are affixed on appliances and equipment generally used by ordinary non instructed people (e.g in the field of domestic appliances). A mark of conformity is delivered by certification body if the equipment meet the requirements from an applicable standard and after verification of the manufacturer’s quality management system.
Certification of Quality
The standards define several methods of quality assurance which correspond to different situations rather than to different levels of quality.
A laboratory for testing samples cannot certify the conformity of an entire production run: these tests are called type tests. In some tests for conformity to standards, the samples are destroyed (tests on fuses, for example).
Only the manufacturer can certify that the fabricated products have, in fact, the characteristics stated.
Quality assurance certification is intended to complete the initial declaration or certification of conformity.
As proof that all the necessary measures have been taken for assuring the quality of production, the manufacturer obtains certification of the quality control system which monitors the fabrication of the product concerned. These certificates are issued by organizations specializing in quality control, and are based on the international standard ISO 9001: 2000.
These standards define three model systems of quality assurance control corresponding to different situations rather than to different levels of quality:
- Model 3 defines assurance of quality by inspection and checking of final products.
- Model 2 includes, in addition to checking of the final product, verification of the manufacturing process. For example, this method is applied, to the manufacturer of fuses where performance characteristics cannot be checked without destroying the fuse.
- Model 1 corresponds to model 2, but with the additional requirement that the quality of the design process must be rigorously scrutinized; for example, where it is not intended to fabricate and test a prototype (case of a custom-built product made to specification).