On Sun, 8 Dec 2013 09:42:47 -0800 (PST), Edge
wrote:

At this home there is a 20 amp breaker in the electrical panel that is pencil labeled as for the dishwasher and garbage disposal. At the junction box on the kitchen wall near the sink we see the 12 gauge wire feeds from the panel. Three 14 gauge wires, hot-black/neutral-white/ground-green, are routed from this box to another junction box underneath the sink through conduit. A whip from the dishwasher is hardwired to the wires under the sink.

We want to add a GE half horsepower garbage disposal that is suppose to draw only 4.5 amps. Can we just pull another hot 14 gauge wire for the garbage disposal and use the existing white neurtal already there for the dishwasher? Does it matter whether 14 gauge is used rather than 12 gauge wires for either device?

My possibly not-to-code answer. Unless you plan to run the disposal
for long periods of time, like 10 or more minutes at a time, I
personally would not worry about it and just add the circuit. The
only time the load would be particularly high would be if you happened
to run the dishwasher and disposal at the same time and as I said,
unless you are planning on marathon disposal sessions you just won't
be loading the circuit long enough to be an issue.