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TW wire was 'the norm' from when to when?

13 years ago

Just doing a little "forensic" analysis on an older building, before pros show up to bid on the big re-wire, re-PANEL, conversion of overhead service drop to buried, etc.

Anyway, it's all EMT, metal boxes, and TW copper conductors... SIX different brands of TW, obviously from different eras, judging by the "age" of the rubber, the style of fonts/graphics printed on the rubber, etc... figured the original builder used only 1 or 2 brands of TW back in the early 1950s, and the other brands came from the increasingly bad "work" since then. At some point the "upgrades" stopped, because there's no 90C wire (e.g. THHN) to be found.

Just curious as to what years TW (60C, rubber insulation) was "standard issue", and when the change to 90C wire (thermoplastic insul.) occurred?

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