DIYbanter - View Single Post - Circuit breaker tester maps to wrong breaker!!

(Chip C) writes:
Probably all the cables are close together somewhere, going through a
joist or a sill. In fact, they may be *too* close, for too long a
stretch, by current code, but it's hard to know if this is worrisome
enough to start tearing up walls.

Hmmm... I didn't realize that code prevented cables running
together. Does this apply to cable bundles in the basement? I always
thought that running cables together was a sign of neat workmanship
(vs. a scattered spider's web of cabling) rather than against code.

Can you explain what the code says here?