Low Voltage Safe Work Practices

This article is about safe word practices at plants and refineries during work on low voltage equipment.

Low Voltage Safe Work Practices

1. Energized Control Circuits (240 Volts and Lower)

Working on energized control circuits rated at 240 volts and lower is subject to specific conditions and safety protocols to ensure the well-being of personnel and equipment. Here are the guidelines and explanations:

1. Permissible Tasks:

  • Personnel are allowed to perform the following tasks on energized control circuits rated at 240 volts and lower:
    • Testing
    • Adding jumpers
    • Changing out control devices

2. Personal Protective Equipment (PPE):

  • It is mandatory for all individuals involved in these energized circuit tasks to wear the appropriate Personal Protective Equipment (PPE) as specified in Appendix A. PPE helps safeguard personnel from potential electrical hazards.

3. Authorized Personnel:

  • Only Fully Authorized personnel, with the required level of training and authorization, are permitted to engage in energized circuit work on control circuits rated at 240 volts and lower. This designation ensures that personnel possess the necessary skills and knowledge to perform such tasks safely.

4. Temporary Authorization:

  • In certain circumstances, related personnel may receive temporary authorization to work on energized control circuits rated at 240 volts and lower, even if it falls outside the scope of their original training. This is contingent upon a mutual agreement between the individual performing the task, a Qualified Electrical Leader, and a site or plant manager. All parties must collectively assess the individual’s competence and capability to safely carry out the required task(s).

5. Jumper and Test Equipment Installation:

  • Qualified individuals are permitted to install clip-lead jumpers or test-equipment leads on control circuits rated at 240 volts and lower. This includes tasks such as connecting or disconnecting permanently installed energized wires on control or alarm circuits for purposes like calibration or facilitating the removal/installation of control devices associated with critical process equipment. During such activities, personnel must adhere to the specified PPE requirements outlined in Appendix A.

Adhering to these procedures is crucial to ensure the safety of personnel while performing tasks on energized control circuits rated at 240 volts and lower. Additionally, strict compliance helps maintain the integrity and reliability of the control systems and equipment involved.

2. Energized Control Circuits (240 Volts and Lower)

Working on energized control circuits rated at 240 volts and lower is governed by specific conditions and safety protocols to ensure the safety of personnel and equipment.

Engagement in Permissible Tasks:

  • Task Description: Personnel are permitted to engage in tasks involving energized control circuits rated at 240 volts and lower. These tasks include testing, adding jumpers, and changing out control devices.
  • This guideline defines the scope of permissible tasks to maintain clarity and ensure that personnel only perform authorized activities on these circuits, reducing the risk of errors or unsafe practices.

Utilization of Personal Protective Equipment (PPE):

  • PPE Requirement: All individuals involved in these energized circuit tasks must adhere to the specified Personal Protective Equipment (PPE) requirements outlined in Appendix A.
  • Emphasizing the use of PPE is essential to safeguard personnel from potential electrical hazards, aligning with the principle of “Assure Safety.”

Authorization of Personnel:

  • Authorized Personnel: Only Fully Authorized personnel, who have received the necessary training and authorization, may engage in energized circuit work on control circuits rated at 240 volts and lower.
  • Temporary Authorization: In some cases, personnel may receive temporary authorization for tasks outside their original training scope, subject to agreement between the individual, a Qualified Electrical Leader (Q-EL), and a site or plant manager. This ensures competent and capable personnel perform the work.
  • These measures align with the “Authorize and Train” principle, ensuring that only qualified individuals handle energized circuits, promoting safety and competence.

Installation of Jumpers and Test Equipment:

  • Qualified Individuals: Qualified individuals may install clip-lead jumpers or test-equipment leads on control circuits rated at 240 volts and lower. This includes activities like connecting or disconnecting energized wires for calibration or control device maintenance.
  • Allowing qualified personnel to perform these tasks while adhering to PPE requirements ensures that essential maintenance or calibration activities are conducted safely, aligning with the principle of “Train and Equip.”

Compliance with these procedures is paramount to uphold safety and the proper functioning of control systems and equipment.

3. Low-Voltage Motor Control Centers, Power, and Distribution Panels

Adding bolted molded-case circuit breakers or fused disconnects to power and distribution panels or Motor Control Centers requires adherence to safety protocols. Here are the guidelines along with explanations where needed:

1. Panel De-energization Requirement:

  • De-energize Before Modification: Before adding bolted molded-case circuit breakers or fused disconnects, it is strictly prohibited to modify power and distribution panels or Motor Control Centers while they are energized.
  • Explanation: This rule ensures that any work on these panels is carried out under safe conditions and adheres to the “Assure Safety” principle.

2. Energized Bus and PPE:

  • Energized Bus Work: In cases where it is necessary to remove or insert a low-voltage motor control center plug-in unit onto an energized bus, the personnel performing this task must wear the appropriate Personal Protective Equipment (PPE) as specified in Appendix A.
  • Full Authorization: Only Fully Authorized personnel are allowed to engage in such activities while considering their safety by wearing the required PPE.
  • This guideline emphasizes safety and the importance of qualified personnel wearing PPE, aligning with the “Assure Safety” principle.

Low-Voltage Terminal Boxes

Maintenance involving low-voltage terminal boxes requires specific safety measures. Here are the guidelines and explanations:

3. Voltage Absence Check:

  • Mandatory Voltage Check: Prior to conducting maintenance on low-voltage terminal boxes, it is mandatory to check for the absence of voltage.
  • PPE Requirement: During this process, individuals must wear the appropriate Personal Protective Equipment (PPE) as indicated in Appendix A.
  • This guideline ensures that voltage presence is verified, reducing the risk of electrical incidents, and it emphasizes the use of PPE for safety in line with the “Assure Safety” principle.

4. Low Voltage Buses

Performing work on the main bus of a Low Voltage Motor Control Center (LV MCC) or Switchgear necessitates comprehensive safety measures. Below are the guidelines, along with explanations as needed:

1. Prior Review and Approval:

  • Review by Q-EL: Before commencing any work on the main bus of an LV MCC or Switchgear, the work must undergo a thorough review and approval process by a Qualified Electrical Leader (Q-EL).
  • Task Descriptions: A set of task descriptions is required to configure the system for the work. Please refer to Appendix C1 for task descriptions, which should be attached to the Safety Work Permit.

2. Restoration Task Descriptions:

  • Restore Electrical System: To return the electrical system to its normal state after the work is complete, another set of task descriptions must be employed.
  • Appendix C2: Task descriptions for system restoration can be found in Appendix C2, which should also be attached to the Safety Work Permit.

3. Safety Work Permit Requirement:

  • Safety Work Permit Issuance: For any work involving the LV bus, a Safety Work Permit must be issued. Additionally, a separate Safety Work Permit is needed for the activities required to restore the system to normal operation.
  • Isolation and Back Feed Elimination: The primary aim of this procedure is to identify and isolate all supply sources while eliminating the possibility of electrical back feed.

4. Scope Change Protocol:

  • Work Scope Change: In the event that the scope of work changes during the course of the project, work must cease immediately. Subsequently, the current Safety Work Permit and the checklist provided in Appendix C1 will be canceled.
  • New Permit and Checklist: A new Safety Work Permit and a revised set of task descriptions and checklist (Appendix C1) that align with the updated work scope must then be issued.

5. Multiple Power Sources:

  • Identification and Lockout-Tagout: When working on LV motors or equipment powered by more than one source, it is essential to identify and implement lockout and tagout procedures for all power sources connected to that equipment. For instance, if a low voltage motor with a space heater is involved, both the power leads and the heater leads must be locked out and tagged out before any work is allowed on the equipment.

These guidelines are in place to ensure the safety of personnel working on LV buses, prevent electrical hazards, and maintain strict control over the work scope. Adhering to these protocols aligns with the “Assure Safety” principle.

5. Low-Voltage Electrolytic Cell Lines (Less than 400 Volts DC, Greater than 1,000 Amps DC)

Working in low-voltage electrolytic cell lines involves unique safety requirements and precautions. Below are the guidelines and explanations:

1. Personal Protective Equipment (PPE):

  • EH-Rated Work Boots: Personnel within the cell line working zone (CLWZ) are mandated to wear electrical hazard (EH)-rated work boots. This is in addition to wearing the appropriate PPE as detailed in Appendix A.
  • Minimum Base Electrical PPE: The minimum base electrical PPE required within the CLWZ is Category 1 PPE.

2. De-Energization and Isolation:

  • Cell Switch Operation: Before performing any work on cell flexible cables, cable termination points, etc., the respective cell must be bypassed (shorted) and isolated using cell switches.
  • Zero Volts and Zero Amps: Prior to switching activities, the rectifier output should be set to zero volts and zero amps. This ensures that the system is de-energized.
  • Battery Voltage Reminder: Be cautious that each de-energized cell may still contain “battery voltage,” typically less than 2.5 volts DC.

3. Voltage Verification:

  • DC Voltage Testing Challenge: Non-contact voltage testers for DC voltage do not exist. Verification for the absence of DC voltage must be carried out using the cell voltage monitoring device, following a “test before touch” approach.
  • Site-Specific Procedures: Each electrolytic cell line plant will have its own site-specific procedures to perform this verification. Voltage should be less than nominal cell voltage (usually 12 volts DC) and decreasing. The voltage monitoring device’s correct operation should be verified both before and after cell de-energization.

4. Earth/Ground Connections:

  • Main Earth/Ground Connections: The rectifier’s DC power system’s main earth/ground should be connected to the cell line structural steel at a minimum of two points.
  • Diagnostic Testing Reference: During diagnostic electrical testing (e.g., insulation resistance or voltage tests), the cell line structural steel serves as the earth/ground reference.

5. High-Voltage Rectifier Precautions:

  • De-Energization and Lockout: When working on the DC bus system of the electrolytic cell line, the rectifier’s input power must be de-energized and locked out in accordance with procedure 25-010532.
  • Bus Isolation: Isolate all cells from the DC bus system to prevent battery voltage backfeed. Use an approved DC voltage contact tester for verification.
  • Safety Grounds/Earthing Conductors: Apply safety grounds/earthing conductors to the rectifier output positive and negative bus. Ensure all sections of the DC bus system to be worked on are properly grounded/earthed.
  • High Voltage Electrical Isolation Competence (HVEIC): If the rectifier’s input power is high voltage, an HVEIC is required to work on the HV section of the rectifier or its transformer.

6. Limited Workspace Precautions:

  • Workspace Limitations: When working in tight spaces with less than 42 inches (1.1 meters) available, precautions must be taken. These include either de-energizing the adjacent cell(s) or using non-conductive barriers to prevent contact with energized cells. The use of clean dry leather gloves, voltage-rated gloves, and insulated tools is mandatory.
  • Note: The “edge of cell” may refer to the cell feet, which can extend beyond the cell head.

7. Cell Line without Cell Switches:

  • De-Energization and Lockout: In cell lines without cell switches, the rectifier supplying DC power to the cell line must be de-energized and locked out before any disconnection or connection of cell flexible cables.
  • Voltage Verification: Verify the absence of DC voltage using the cell voltage monitoring device, following a “test before touch” procedure.

8. Magnetic Flux Density Warning:

  • High Magnetic Fields: In CLWZ areas where personnel may be exposed to magnetic flux densities exceeding 10 Gauss, permanent warning signage indicating the presence of a high magnetic field is mandatory.
  • Restriction for Implant Devices: Employees with implanted pacemakers, ferromagnetic medical devices, or other life-critical electronic devices are generally not permitted in cell areas unless expressly authorized by the plant manager following consultation with the company medical officer.

9. DC Bus Insulation Monitor Alarms:

  • Low Alarm: If the DC Bus Insulation Monitor indicates a low alarm, indicating an increased electrical hazard, routine work inside the CLWZ is not permitted.
  • Malfunction Alarm: If the DC Bus Insulation Monitor indicates a malfunction alarm, suggesting a potential electrical hazard, routine work inside the CLWZ is also not allowed.
  • Troubleshooting and Resolution: Immediate steps should be taken, within a maximum of 24 hours, as per local procedures, to identify the source of the alarm and either isolate or rectify the issue.

10. Insulation of Grounded Structural Steel:

  • Insulating Material Installation: Non-conductive insulating material must be installed on all grounded, permanently affixed structural steel supports or members within the CLWZ, up to a height of 60 inches (1.5 meters).
  • Protection from Energized Parts: Grounded metalwork near energized surfaces outside the CLWZ should be insulated to prevent accidental contact with energized parts.

11. Rectifier Power Feeds Identification:

  • Multiple Power Feed Identification: Rectifiers may have multiple electrical power feeds, including high voltage, low voltage, and UPS control power sources. Employees must refer to site-specific drawings to identify all forms of electrical energy.

Following to these safety measures is critical to safeguard personnel and equipment in low-voltage electrolytic cell lines. These guidelines promote a culture of safety and help ensure the reliability and integrity of the work environment.

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