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Use of Rubber Gloves & Protectors for Underground Cable Splicing. Joseph P. Carey, PE Principal Engineer National Grid. Purpose. National Grid is reviewing a work methods change that may require the use of rubber gloves & protectors while splicing medium voltage underground cables.

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use of rubber gloves protectors for underground cable splicing

Use of Rubber Gloves & Protectors for Underground Cable Splicing

Joseph P. Carey, PE

Principal Engineer

National Grid

purpose
Purpose
  • National Grid is reviewing a work methods change that may require the use of rubber gloves & protectors while splicing medium voltage underground cables.
current work practice
Current Work Practice

CONDUCTOR

SHEATH

MH

J

Bonding

Splicer

Bracket GND

Bracket GND

Ground Rod

  • Isolated, Red Tagged, Tested De-Energized and Grounded (with Bracket Grounds)
  • & Work Bare Handed
background
Background
  • National Grid made many contacts throughout the industry to review other utilities UG grounding procedures and work methods.
  • National Grid reviewed existing studies on step and touch potential on underground distribution systems.
findings
Findings
  • Various studies have identified step & touch potential hazards from an accidental energization or a fault from an adjacent circuit, in the order of several thousand volts.
  • There are many different views and approaches to UG grounding across the industry. Approaches include: Establishing an Equipotential Zone, Insulation, and Isolation.
national grid study
National Grid Study
  • Early 2008 a decision was made to perform an internal study. The decision to perform the study was based on the need for data that would represent the National Grid system.
  • National Grid is currently working to complete this study.

Source Substation

Side 1

MH

Side 2

CONDUCTOR

SHEATH

Core (Side 2)

Bonding

Core (Side 1)

Sheath (Side 1)

Sheath (Side 2)

Vs

Ground Rod

study observations to date
Study Observations to Date
  • National Grid’s study confirmed the potential hazards identified in previous studies.
  • Further results from National Grid’s study indicated:
    • Accidental Energization
      • The EPZ Mat is effective at reducing potential hazards when a cable is under repair.
      • The best location for bracket grounds:
        • With an EPZ mat, is close to the work site
        • Without an EPZ mat, the grounds at the substation
    • Fault On an Adjacent Circuit
      • Installing Bracket grounds close to the work site significantly reduces voltage levels
      • In some situations the use of an EPZ mat can increase touch potentials
rubber glove evaluation
Rubber Glove Evaluation
  • The evaluation of undergroundsplicing with rubber gloves was performed at the Millbury Learning Center.
    • A 15kV hand applied splice was built on 1/C 1000MCM Al XLPE Cable. The splice was built with Class 2 Rubber Gloves and Protectors.
    • A 15kV Cold Shrink Splice was built on 1/C EPR 500MCM CU EPR Cable. The splice was built using Class O Rubber Gloves and Protectors.
    • A 15kV Live Seal Stop End was built on 3/C PILC 350MCM Jacketed Cable. The splice was built using Class 2 Gloves and Protectors. Midway through the splicing process the splicer switched to Class 1 Gloves and Protectors.
splicing observations15
Splicing Observations
  • The contaminants from the rubber glove protectors were transferred to the splice.
    • Metal filings, compounds, oils & leather material
    • The contaminants observed raised a concern of the level of the reliability of the splice.
  • Oil & compounds migrated through the protectors to the rubber gloves.
    • There may be an issue with degradation of rubber gloves when using oil based tapes and silicon tapes.
  • The towelettes that are used to clean the cable were contaminated by the protectors.
  • Dexterity may be an issue with some of the splicing tasks.
astm committee input
ASTM Committee Input
  • It is National Grid’s determination that there is a potential for damage to the rubber gloves when used without protectors during some cable splicing activities.
  • National Grid is seeking the help of the ASTM sub-committee for further exceptions or alternatives to the current leather protector requirements.
    • Different style leather protector (coated)
    • Exception of using protectors on rubber gloves Class 1 and higher
    • Other solutions