What factors should be considered for the selection of electrical equipment according to external influences?

What factors should be considered for the selection of electrical equipment according to external influences?

Regulation 512.2.4 states:

"The selection of equipment according to external influences is necessary not only for proper functioning, but also for the reliability of the measures of protection for safety complying with BS 7671 generally. Measures of protection afforded by the construction of equipment are valid only for the given conditions of external influence if the corresponding equipment specification tests are made in these conditions of external influence.

NOTE: For the purpose of BS 7671, the following classes of external influence are conventionally regarded as normal:

• AA Ambient temperature: AA4
• AB Atmospheric humidity: AB4
• Other environmental conditions (AC to AS): XX1 of each parameter
• Utilization and construction of buildings (B and C): XX1 of each parameter, except XX2 for the parameter BC"

This regulation emphasizes that when selecting electrical equipment, it is crucial to consider the external environmental conditions where the equipment will be used. This ensures that the equipment functions correctly and that all safety measures are reliable. The protection provided by the equipment is only effective if the equipment has been tested under the specific external conditions it will face.

For the purpose of BS 7671, the following conditions are considered normal and should be used as a standard reference:

• Ambient Temperature (AA): The typical temperature conditions expected in the environment where the equipment is used.
• Atmospheric Humidity (AB): The usual humidity levels in the environment.
• Other Environmental Conditions (AC to AS): Any additional environmental factors such as pollution or mechanical impact.
• Utilization and Construction of Buildings (B and C): Conditions related to how buildings are used and constructed, with a specific exception for parameter BC which should be considered slightly differently.

Frequently Asked Questions

Q: What does "AA4" and "AB4" mean in this context?

A: Regulation 512.2.4 specifies these codes to represent the severity levels of ambient temperature (AA4) and atmospheric humidity (AB4). These levels correspond to standard conditions expected in most environments.

Q: Why is it important to consider external influences when selecting equipment?

A: According to Regulation 512.2.4, considering external influences ensures that the equipment will not only work correctly but also maintain safety standards under the conditions it will actually face. This prevents failures and potential hazards.

Q: What are "other environmental conditions" (AC to AS)?

A: Regulation 512.2.4 includes these conditions which cover factors like pollution levels, mechanical impacts, vibrations, and other physical or chemical influences that might affect the performance and safety of the equipment.

Q: How do "utilization and construction of buildings" influence equipment selection?

A: The way buildings are used and constructed can impact the environmental conditions inside them. For instance, industrial buildings might have different temperature and humidity levels compared to residential buildings, thus requiring different considerations for equipment selection (Regulation 512.2.4).

Q: What is meant by "XX1 of each parameter" and "XX2 for the parameter BC"?

A: "XX1" and "XX2" in Regulation 512.2.4 denote specific levels of environmental conditions. "XX1" typically represents normal conditions, while "XX2" might represent a slightly more severe or specific condition, especially for the parameter BC (related to building construction specifics).