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 J MH Splicer
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
CONDUCTOR
Side 1 MH
Side 2
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 underground splicing 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?