Installing tankless water heater - 18kW, requires 2 x 40A circuits.
I have a lot of 8ga Black TW wire AND 3/4” conduit.
Is TW still legal ( I have some THHN, but want to use up the TW where I can)?
Can I run both circuits in one conduit?
Can I use a single ground for both circuits?
Is painting the ends or color coding with tape adequate for identification?
What issues am I overlooking?