I was in a old house today thats getting gutted and noticed some tray cable. Its like 12 or 14 stranded. I was not able to snap a photo and whatever it went to is gone. I thought it was some kinda UF or NM but it said TC and the weird color code I recognize as tray cable, I think the orange was used as a ground. Seems just as good as romex but got me wondering was this ever allowed?