Running new cable through or under joists?

My understanding is that #8nmc can be attached to the bottom of joists, but #10nmc must run through holes in them. Is that correct?
I need to run two new cables, a 10/3 and a 12/2. If I ran them together, they would have more mass than a 8/2. Can I attach them to the bottom of the joists, or is code real specific on the matter?
Thanks.
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The code on running exposed cables on bottom of beam: minimum 8/3 or 6/2

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You can also install a running board next to the cables to protect them and make it legal

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Partially. 8/3 may be attached to the bottom of joists, but 8/2 may not.

No. Code is "real specific":
"Where the cable is run at angles with joists in unfinished basements, it shall be permissible to secure cables not smaller than two No. 6 or three No. 8 conductors directly to the lower edges of the joists. Smaller cables shall either be run through bored holes in joists or on running boards. Where run parallel to the joists, cable of any size shall be secured to the sides of the joists in accordance with Section 300-4(d).
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You should run them through the joists, with a hole drilled mid-point where needed. If attached to the bottom of the joists, use metal conduit.
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wrote:

Why metal rather than plastic?
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