Please settle an office discussion. Are there any advantages of using EMT
over interlocked MC cable for 20 Amp branch circuit wiring. Note: An
equipment grounding conductor will be pulled in each. The application is in
commercial construction in of all types (block walls, metal stud walls, some
exposed conduit runs). I am interested in the engineer's, electrician's, as
well as cost perspectives.
Thanks in advance
A more direct comparison would be FMC vs MC but the major difference between a
"cable" and a "raceway" is labor vs flexibility of use. You can pull in another
conductor set in a raceway if your needs change. You are pretty much stuck with
what was in a cable when you installed it. That might be important if the
installation will end up behind drywall.
Exposed, EMT is a bit more resistant to physical damage and it can be buried in
non-cinder concrete. There are places where you simply can't use MC but I
assume you are just talking about a dry location, no particular exposure to
EMT allows for future alterations while MC is about all you get for the
future. Remember, the electrical installations may be there for 40 or 50
years. During that time many alterations will probably be required by many
occupants of the premises. MC limits the flexibility to the original
installation while EMT allows the existing conductors to be removed and
replaced with future configurations.
I am presently working in a facility that is over 50 years old and we daily
remove old wire and install new wire to update the older system by adding
safety devices to meet current codes. Safety standards are updated on a
regular basis. While MC may meet current standards the future will require
many alterations to keep current. Also the premises may change types of
occupancy. For instance many shopping malls now have dental and doctors'
In my area most electrical contractors these days will use MC whenever and
wherever possible. In fact, if EMT isn't specified in the contract, MC is
pretty much what you will get........like it or not. Small commercial jobs
are just about all MC these days.. Larger commercial jobs will usually have
EMT from the distribution panels to boxes set in strategic locations, with
MC for the rest of the wiring. This method is particularly advantageous in
office buildings (where tenants come and go)........usually the floor is
gutted and built to suit the new tenant.....or an existing tenant just wants
a change in layout. The homeruns in the EMT are simply reused, or
additional HR's pulled in. While EMT and Rigid Metal Conduit still have
their uses, MC has replaced EMT as the "preferred" wiring method pretty much
the same way that EMT replaced RMC (GRC at the time)......ease of
installation and reduced cost.
As an electrician I personally think MC sucks because of the way it gets
terminated, but hey, if that's what I'm told to install, and it meets code,
that's what goes in. I'm sure that if baling wire were "legal", that's what
would be getting installed.