On last night’s 2 a.m. restore, we were closing a cutout on a 12.47 kV circuit and everyone kept saying “watch your 12k,” even though phase-to-ground is 7.2. Is that just shorthand from the line-to-line rating, or is there an older reason linemen stuck with it during outage work?
We call it “12k” because circuit names, maps, and gear ratings are line-to-line — “12 kV class” — even though your exposure is 7.2 to ground on a 12.47 grounded-wye. On night restores I’ll read back, “closing on 12k, 7.2 to ground,” so nobody mixes numbers. Small caveat: delta or ungrounded systems don’t follow the 7.2 rule — like coffee at 2 a.m., handle with care.
On a 2 a.m. close on 12.47, it’s radio shorthand and it matches how PPE/MAD get picked by system class, not the phase voltage — . I’ll say “12k class, 7.2” in the tailboard and write it on the switching sheet so the nickname doesn’t bleed into clearances when we’re closing that cutout. Small caveat: delta corners or odd backfeed can make that assumption wrong, so a quick peek at 1910.269 tables helps: 1910.269 - Electric power generation, transmission, and distribution. | Occupational Safety and Health Administration — you mark it that way too?
And old delta habits linger — when a leg floats or you’ve got backfeed, phase potential can creep higher than the textbook 7.2, so saying “12 kV class” keeps everyone thinking by system class. My tip: I write it both ways on the tailboard and radio it as “12k class, 7.2 phase,” especially for new hands; @ella3865, do your maps still carry the class label?
Dispatch labels and SCADA are line‑to‑line, so the radio sticks with ‘12k’ even when you’re closing that 2 a.m. cutout at 7.2 to ground. The gear you’re touching is 15 kV nameplate and regs can float the bus a tad high, so saying 12k keeps us in the bigger envelope; ever notice the PT shows 7200:120 while the sub board says 12 kV?
But one more reason we stick with “12k”: during single‑phase switching, PTs/open‑delta banks can kick overvoltage (ferroresonance/backfeed), so the line‑to‑line label keeps everyone thinking worst‑case instead of the textbook nominal. I’ll call the feeder “12k” and then state the expected phase potential at the cutout (about 7 kV to earth); @lucas_mar20 do you guys say both or just “12k”?