Use of Rubber Gloves & Protectors for Underground Cable Splicing

1. Use of Rubber Gloves & Protectors for Underground Cable Splicing Joseph P. Carey, PE Principal Engineer National Grid

2. Purpose • National Grid is reviewing a work methods change that may require the use of rubber gloves & protectors while splicing medium voltage underground cables.

3. 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

4. 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.

5. 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.

6. 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

7. 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

8. 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.

9. Splicing Observations

10. Splicing Observations

11. Splicing Observations

12. Splicing Observations

13. Splicing Observations

14. Splicing Observations

15. 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.

16. 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

17. Questions?