Presentation on theme: "Use of Rubber Gloves & Protectors for Underground Cable Splicing Joseph P. Carey, PE Principal Engineer National Grid."— Presentation transcript:
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.
Current Work Practice CONDUCTORSHEATH MH Isolated, Red Tagged, Tested De-Energized and Grounded (with Bracket Grounds) & Work Bare Handed Ground Rod Bonding Splicer Bracket GND
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 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 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. CONDUCTORSHEATH MH Ground Rod Bonding Core (Side 1) Vs Side 1Side 2 Source Substation Sheath (Side 1) Core (Side 2) Sheath (Side 2)
Study Observations to Date National Grids study confirmed the potential hazards identified in previous studies. Further results from National Grids 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 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.
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 It is National Grids 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