When using 10-2 wire for a 3 wire dryer can the neutral wire be the uninsulated ground wire or does it have to be insulated?
You need 10-3 PLUS ground for this 220v application. The ground
is the only uninsulated wire. If you did it with 10-2, I would
suggest re-doing it correctly ASAP. That leaves you without a
neutral and potential for supply to go through grounding wire to
breaker box (or through a person to ground, causing
Clarification: you do not need three current-carrying conductors
for all 220 v applications. There is no neutral in 220, so you only
need two "hot" leads and a bare safety grounding wire. If the
appliance (as here, a dryer) actually needs 110 in addition to 220,
then yes, you need 10/3 cable, plus grounding wire.
First of all the word "shield" in electricity refers to blocking
magnetic flux. What you meant to say is "insulated" which means to
block conductivity. When #?-2 NM w/ Ground wire is used in a 240
volt circiut, there is no neutral conductor. You're connecting the
black and white wires hot and the bare wire as equipment ground in
the distribution panel. On the dryer a 3 wire cord is connected
with the neutral and ground terminals jumpered, so that the ground
wire ran to the dryer serves as both ground and neutral. This is
how dryers have been wired for many years in most of North America.
Electrically this works because ground and neutral have the same
electrical potential. Technically, however, it's wrong because a
ground wire shouldn't be used as a normally current carrying
conductor, and in the case of a dryer, the motor and control
circuits are 120 volt, causing a small current flow in the ground
conductor with a 3 wire supply.
The real question is: Does a residential dryer require a
separate neutral conductor or just a ground conductor? The same
question asked differently does a residential dryer require a #10-2
or #10-3 supply cable?
The answer is: If this is an existing dryer supply, a #10-2
cable with a 3 prong cord will work just as well as it has for
decades, but if this is a new installation, a #10-3 cable and a 4
prong cord is required to abide with current laws.