Who is using UV rated wire for the secondary wiring of CTs/VTs where the instrument transformers are exposed to the elements?
Minnesota Power has seen a number of issues with open circuited CTs, overburdened CTs, or missing potentials on meters where standard THHN or THHW wire was used. After 5-10 years in the field the insulation rots off and the copper disintegrates completely.
In response to this we have started using XHHW. After 8-10 years of being in the field most installs still look like brand new. The only down side to using this is a #12 XHHW wire is slightly thicker than a #10 THHN wire. On a 9S install where we use #12 for voltages and #10 for currents we had to upside to 1.25 inch conduit instead of our usual 1 inch because it got too tight to pull through.
MP’s standards call for #12 wire for voltage circuits and a minimum of #10 wire on CT secondary circuits. We also require all stranded wire, no solid core wire.
The Upper Midwest Metering Association serves the upper midwest states of Minnesota, Iowa, Wisconsin, South Dakota, and North Dakota. We provide connections for members, utilities, meter schools, and vendors in our bi-annual meetings and continuous dialog throughout the year.