Architecture assessment criteria

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Certain decisive criteria are assessed at the end of the 3 stages in defining architecture, in order to validate the architecture choice. These criteria are listed below with the different allocated levels of priority.

On-site work time

Time for implementing the electrical equipment on the site.

Different levels of priority

  • Standard: the on-site work time can be extended, if this gives a reduction in overall installation costs,
  • Special: the on-site work time must be minimized, without generating any significant excess cost,
  • Critical: the on-site work time must be reduced as far as possible, imperatively, even if this generates a higher total installation cost,

Environmental impact

Taking into consideration environmental constraints in the installation design. This takes into account the: consumption of natural resources, Joule losses (related to CO2 emission), “recyclability” potential, throughout the installation’s lifecycle.

Different levels of priority:

  • Non significant: environmental constraints are not given any special consideration,
  • Minimal: the installation is designed with minimum regulatory requirements,
  • Proactive: the installation is designed with a specific concern for protecting the environment (low ernergy building, green buildings, etc.).

The environmental impact of an installation will be determined according to the method carrying out an installation lifecycle analysis, in which we distinguish between the following 3 phases:

  • construction,
  • operation,
  • end of life (dismantling, recycling).

In terms of environmental impact, 3 indicators (at least) can be taken into account and influenced by the design of an electrical installation. Although each lifecycle phase contributes to the three indicators, each of these indicators is mainly related to one phase in particular:

  • Manufacturing phase mainly impact the consumption of natural resources (steel, copper, aluminium),
  • Operation phase impacts mainly the energy consumption (power losses cumulated during all the operating period).
  • End of life is mainly impacted by the recyclability potential of equipment and material (presence of hazardous material, quantity of insulation material).

The following table details the contributing factors to the 3 environmental indicators (Fig. D5).

Fig. D5 – Contributing factors to the 3 environmental indicators
Indicators Contributors
Natural resources consumption Mass and type of conductor material: copper, steel, aluminium
Power consumption Joule losses in conductors, transformers, no-load losses of transformers
"Recyclability" potential Mass and type of insulation material, presence of hazardous material.

Preventive maintenance level


Number of hours and sophistication of maintenance carried out during operations in conformity with manufacturer recommendations to ensure dependable operation of the installation and the maintaining of performance levels (avoiding failure: tripping, down time, etc).

Different categories:

  • Standard: according to manufacturer recommendations.
  • Enhanced: according to manufacturer recommendations, with a severe environment,
  • Specific: specific maintenance plan, meeting high requirements for continuity of service, and requiring a high level of maintenance staff competency.

Availability of electrical power supply


This is the probability that an electrical installation be capable of supplying quality power in conformity with the specifications of the equipment it is supplying. This is expressed by an availability level:

Availability (%) = (1- MTTR/ (MTBF + MTTR)) x 100

MTBF (Mean operating Time Between Failures - also MOTBF) = the average time for which the electrical system is operational and therefore enables correct operation of the equipment;
MTTR (Mean Time To Restoration) = the average time to make the electrical system once again operational following a failure (this includes detection of the reason for failure, its repair and re-commissioning).

The different availability categories can only be defined for a given type of installation. E.g.: hospitals, data centers.

Example of classification used in data centers

Tier 1 = the power supply and air conditioning are provided by one single channel, without redundancy, which allows availability of 99.671%
Tier 2 = the power supply and air conditioning are provided by one single channel, with redundancy, which allows availability of 99.741%
Tier 3 = the power supply and air conditioning are provided by several channels, with one single redundant channel, which allows availability of 99.982%
Tier 4 = the power supply and air conditioning are provided by several channels, with redundancy, which allows availability of 99.995%

Fig. D6 – Definition of MTBF and MTTR