Electrical Safety: Preventing Contact and Indirect Faults

Electrical Safety: Prevention and Protection

1. Preventing Direct Contact with Electrical Networks

To prevent accidental contact between a person and an electrical grid, which can cause conductive coupling, it is crucial to ensure no galvanic connection exists between the two, as the earth naturally provides a galvanic connection. The prevention approach relies on interposing an insulating barrier or supplementary interruption at some point in the network-person-to-ground path.

2. Defining Fault Voltage (UD) and Contact Voltage (UC)

• UD (Fault Voltage): This is the voltage that rises between conductive parts (like metal cabinets) or between these parts and the reference ground in the event of a fault.
• UC (Contact Voltage): This is the fault voltage, or ground voltage, that can appear across a person bridging the gap.

4. Protection Measures Against Direct Contacts (UNE 20460-4-41]

The UNE 20460-4-41 standard defines several means of protection against direct contacts:

• Protection by isolation of live parts.
• Protection by barriers or enclosures.
• Protection by placing components out of reach (allunyamnt - likely meaning adequate separation/distance).
• Protection via residual current devices (diferencals waste - likely meaning residual current circuit breakers).

5. Protective Measures Against Indirect Contacts

Protective measures applicable against indirect contacts include:

• Automatic disconnection of the supply (protection rating).
• Protection through the use of Class II equipment or equivalent insulation.
• Protection in locations with non-conductive floors or surroundings.
• Protection through equipotential bonding connections that are not connected to the main ground.
• Protection via electrical separation.

4. Items Requiring Connection to Ground in an Electrical Installation

The following items need to be connected to the ground in an electrical installation:

• Centralized metering points.
• Metal guides for lifting appliances.
• Overall safety protection enclosures, if metallic.
• Surge protection facilities.
• TV and FM antennas.
• Plumbing, heating, and gas facilities.
• Structural metal reinforcement in concrete walls and supports, and other significant metallic elements.

9. Function and Characteristics of a Voltage Relay Protection

The protection offered by a voltage relay device is designed to prevent the persistence of excessively high voltage on contact areas of the installation that are not part of the active circuit.

Its characteristics are:

1. It causes power outage in all active conductors when it detects a dangerous voltage.
2. It serves to limit the maximum fault voltage to 50 V in dry locations or 24 V in humid locations.
3. It must disconnect the active conductors in the shortest possible time (less than 5 seconds, as indicated by the REBT - Low Voltage Electrical Installation Regulation).