Electrical Safety Procedures: Working Without Voltage

1. Recording Electrical Installation Operations

Operations are performed when an electrical installation is recorded. A facility or discharge is recorded under the following conditions:

• Open and visibly disconnect from all power supply sources.
• Block or lock in the open position, if possible, using cutting devices.

2. The Five DOR Rules for Working Without Voltage

The five DOR (De-energization, Operation, Recognition) rules for prevention and protection work without tension are:

1. Open and visibly disconnect all voltage sources via switches and disconnectors to ensure the impossibility of unforeseen re-energization.
2. Block or lock the cutting devices in the open position, if possible.
3. Verify the absence of voltage.
4. Apply grounding and short-circuiting to all possible voltage sources.
5. Place safety signs delimiting the working area.

3. Causes of Unexpected Re-energization

An electrical installation, even when de-energized, could unexpectedly become energized due to:

• Dropped conductors.
• Induction phenomena.
• Atmospheric discharges.
• Return voltage.

4. Explaining Return Voltage

Return voltage is a voltage that appears if there is a breakdown on Line 1 (main supply) and its switch is not closed when the Line 2 switch (reserve supply) is closed. Photo 1

5. Understanding Device Blocking and Interlocking

Lock or Interlock Definition

Locking or interlocking is the set of operations to prevent the operation of a device, keeping it in a certain position. This prevents any unforeseen cause, human error, or technical failure.

Methods of Blocking and Interlocking

• Physical Block: An insulating element placed between the parts of the cutting device prevents the union of its contacts.
• Mechanical Lock: A lock, padlock, or pin immobilizes the control of the cutting device.
• Electrical Lock: The withdrawal of a fuse from a general protection box prevents the operation of the cutting device because the circuit is open.
• Pneumatic Block: The compressed air supply circuit is emptied, preventing the control switch from being actuated.

6. Verifying Absence of Voltage in Electrical Installations

The absence of voltage is checked on all conductors using voltage detectors. These devices emit a light, sound, or mixed signal. It is essential to check their performance before and after use. Voltage detectors consist of two parts: the probe towards the detector and the insulating handle.

7. Recognizing Absence of Voltage on an Overhead Line

The device used is a cable spear gun, which launches a fuse wire. This wire is placed on the conductors of the line to check for the absence or presence of voltage. If the line has voltage, the wire melts because it causes a short circuit on the conductors.

9. Marking the Electrical Work Area

This consists of defining the work area with tape, signs, and fences to prevent the risk of electrical accidents. Once this operation is completed, the working area becomes a safe space.