Someone else is wiring up an on-demand heater. They need three 50A breakered circuits and they want to run the kaboodle in one conduit.
They want to use #8 THHN wire because it's allowed to 50A @ 75C (all terminations are 75C). However, we run into the conduit fill derate in 310.15(B)(3)(a).
There will be 6 wires, so 80% derate.
OK, being THHN the wire is rated for 90C so the derate comes off the 90C column in 310.15(B)16. That is 55 amps for #8 Cu at 90C.
80% of 55A is 44A.
Now what? Am I obliged to round down, and use a 40A breaker (won't work)? Or am I allowed to round up to the next breaker size (50A)?