UV rated wire in outdoor installs

[Jason ChristoffModerator]

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.

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