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 design has been done according to the latest edition of the appropriate wiring rules
- The electrical equipment comply with relevant product standards
- The initial checking of conformity of the electrical installation with the standard and regulation has been achieved
- The periodic checking of the installation recommended is respected.
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 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:
- Electrical continuity and conductivity tests of protective, equipotential and earthbonding conductors
- Insulation resistance tests between live conductors and the protective conductors connected to the earthing arrangement
- Test of compliance of SELV (Safety Extra Low Voltage) and PELV (Protection by Extra Low Voltage) circuits or for electrical separation
- Insulation resistance/impedance of floors and walls
- Protection by automatic disconnection of the supply
- For TN, by measurement of the fault loop impedance, and by verification of the characteristics and/or the effectiveness of the associated protective devices (overcurrent protective device and RCD)
- For TT, by measurement of the resistance RA of the earth electrode of the exposed-conductive-parts, and by verification of the characteristics and/or the effectiveness of the associated protective devices (overcurrent protective device and RCD)
- For IT, by calculation or measurement of the current Id in case of a fist fault at the line conductor or at the neutral, and with the test done for TN system where conditions are similar to TN system in case of a double insulation fault situation, with the test done for TT system where the conditions are similar to TT system in case of a double insulation fault situation.
- Additional protection by verifying the effectiveness of the protective measure
- Polarity test where the rules prohibit the installation of single pole switching devices in the neutral conductor.
- Check of phase sequence in case of multiphase circuit
- Functional test of switchgear and controlgear by verifying their installation and adjustment
- Voltage drop by measuring the circuit impedance or by using diagrams
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: installations based on class 2 insulation, 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.
After verification and testing an initial report must be provided including records of inspection, records of circuits tested together with the test result and possible repairs or improvements of the installation.
Put in out of danger the existing electrical installations
This subject is in real progress cause of the statistics with origin electrical installation (number of old and recognised dangerous electrical installations, existing installations not in adequation with the future needs etc.)
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.
The following tests should be performed
- Verification of RCD effectiveness and adjustments
- Appropriate measurements for providing safety of persons against effects of electric shock and protection against damage to property against fire and heat
- Confirmation that the installation is not damaged
- Identification of installation defects
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 of employees||
|Other cases||Every 3 Years|
|Installations in buildings used for public gatherings, where protection against the risks of fire and panic are required||According to the type of establishment and its capacity for receiving the public||From one to three years|
|Residential||According to local regulation||Example: the REBT in Belgium which imposes a periodic control each 20 years.|
Fig. A3: Frequency of check-tests commonly recommended for an electrical installation
As for the initial verification, a reporting of periodic verification is to be provided.
Conformity assessment (with standards and specifications) of equipment used in the installation
Conformity of equipment with the relevant standards can be attested in several ways
The conformity assessement of equipment with the relevant standards can be attested:
- By 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 given by the manufacturer
Declaration of conformity
As business, the declaration of conformity, including the technical documentation, is generally used in for high voltage equipments or for specific products. In Europe, the CE declaration is a mandatory declaration of conformity.
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, it completes the declaration of conformity and the technical documents of the equipments
Certificate of conformity
A certificate of conformity can reinforce the manufacturer's declaration and the customer's confidence. It could be requested by the regulation of the countries, imposed by the customers (Marine, Nuclear,..), be mandatory to garanty the maintenance or the consistency between the equipments
Mark of conformity
Marks of conformity are strong strategic tools to validate a durable conformity.It consolidates the confidence with the brand of the manufacturer. A mark of conformity is delivered by certification body if the equipment meets the requirements from an applicable referential (including the standard) and after verification of the manufacturer’s quality management system.
Audit on the production and follow up on the equipments are made globally each year.
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).