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wrote:
I know that the wall between my home and attached garage is a double
thickness of drywall for fire resistance purposes.
Am I violating code or reducing the level of protection by drilling a
hole to bring out a new electrical circuit? Can I place an outlet box
in the firewall? Are there ways I can/should do this to remain
code-compliant?

Thanks.

This is a tough set of questions to answer in a brief posting. First
lets get one thing straight. The objective is to allow firefighters
enough time to save your house from a fire that starts in the garage
rather than to just avoid violating the code. The code contains the
minimum standards of construction to achieve this. The one hour rated
fire wall between your garage and your families home has been built to a
design that has been tested to resist a standard test fire in a test
furnace at a laboratory. In over thirty years of service in fire and
rescue work I have yet to encounter a fire that looked even a little bit
like a test furnace fire. Fire rated assemblies just buy some time for
the fire service to arrive and defend the protected space.

In order to avoid compromising the walls integrity you must keep any
penetrations of the fire wall as small as possible. Whatever you are
running through the wall should just barely fit in the hole. Any gap
around the cable or conduit should be filled with patching plaster if it
is small and fire stopping compound if it is larger. Outlet boxes can
be located in a fire wall but they must be a very tight fit in the
opening. I will guess that you are talking about cutting in a new
outlet using an old work box. If so you must cut the opening as tightly
as possible and fill in any gap around the box with plaster that fills
the gap rather than just dressing the surface. Boxes located in a fire
wall must not be located back to back. Check to be sure that there is
not another box on the other side of the wall located in the same stud
channel.

If I misunderstood the intent of your question please don't give up just
try again. I will help if I can.
--
Tom H