Shared neutral on 20A receps and 50A cook top

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Was in panel for something else.Noticed conduit with (2) #8's going to two pole 50(cooktop)per pnl. sch.(2)#8's to grounded bus.(resi.). (1) #12 going to 20(refrigerator)per sch.Assuming shared neutral.Assume nuetral is sufficient size because it is probably only carring load of 40w appliance bulb (cooktop) and refrig. Is there any code violaion? I would have like to have seen another nuetral.
 
It is probably a code violation because of failure to derate the conductors for four-in-a-raceway and is a multiwire branch circuit that violates 210.4(C).

Because the the neutral is being used as the grounded conductor for the refrigerator circuit, it fails to meet the requirement of 310.15(B)(4)(a). Consequently, there are four CCCs in the conduit, requiring 80% derating.

Eighty percent of the 30 Amps for the #12 is 24 Amps, so that one is ok.

Eighty percent of the 55 Amps at 90 degrees for the #8 is 44 Amps. Since 240.6(A) includes a 45 Amp breaker, you can't put a 50 Amp breaker in the circuit.

With all of the ungrounded conductors served by one neutral, it is probably a multiwire branch circuit. However, it violates 210.4(C) and doesn't qualify for either exception. Fails the code again.
 
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