A Kitchen Remodel 5: Kitchen Electrical

Whenever you remodel a kitchen such as I did, you will run into some issues involving electrical work. Most communities require electrical work to be done by a licenced  electrical contractor unless the homeowner performs the work himself.  Building codes often require outlets in the ends cabinets on peninsula and island counters.  Therefore, even the act of changing out the cabinets requires a basic understanding of electricity.  Fortunately anybody with rudimentary understanding of theatrical lighting should have enough knowledge to undertake many of these tasks themselves.

When I designed the new kitchen layout, we decided to move the microwave from a niche in the upper cabinets next to the refrigerator to a new spot over the range in place of an under-counter fan.  There was power to the existing range hood.  However, it was not a dedicated circuit but was fed by the same breaker as other outlets in the house.  I terminated that feed in an outlet box that I installed in the attic above the kitchen and briefly explored relocating the circuit that had fed the microwave in its old location and which I knew was dedicated to that purpose exclusively.  This was when I ran into a house wiring scheme that I had never seen before.

My previous experience with house wiring involved 2-wire plus ground Non-Metallic Sheathed (NM) wire in 12 and 14 gauge.  This wirning involves 2 conductors (a hot, a neutral) and third ground wire running from the breaker panel and throughout the circuit.  However, when I opened up the outlet for the old microwave, I discovered that the 20-amp microwave circuit was run in tandem with a second 20-amp circuit with 4 wires (3 conductors — red, black & white and one ground) running from the breaker panel in the garage to the microwave outlet utility box.  Under this arrangement, the red and the black wires are both hot and are connected to adjacent breakers in the breaker box.  The microwave outlet used the hot red wire, the neutral white wire and the uninsulated copper (shown green on the diagram) wire.  Meanwhile the other circuit utilized the hot black wire, the neutral white wire and the uninsulated copper wire.  All 4 wires are 12 gauge (meaning that each wire is rated for 20 amps.)

At first, this arrangement seems wrong.  Since the red wire and the black wire are both capable of carrying 20 amps, should the neutral wire not be rated to carry 40 amps? For that matter, if both circuits were to need the ground simultaneously, should not the ground also be rated for 40 amps?  The answer to both questions is no and has to do with those two adjacent breakers.  In the case of my home (and as is usual for service to most homes in the U.S.) 2 legs of 120 volt power are supplied by the service provider to the home.  Each of those legs is 180 degrees out of phase with one another.  In an over-simplification, at any given moment one leg is “pushing” electrons at exactly the same amplitude as the other leg is “pulling” electrons.  Most of the devices in our homes in the U.S. require a maximum of 120 Volts and are connected via their circuits to one or the other of the 2 legs of power.  However, in the case of those few devices that require 240 volts (such as electric rages, electric furnaces, air conditioners and others) the device can be fed between both legs to achieve 240 volts.  I explain this to my students by equating it to that word problem where an airplane is traveling at 120 mph with a 120 mph tailwind, thus traveling at 240 mph relative to the ground.

Since the two wires are out of phase with one another, the maximum amount of  current ever carried by the white or green wire should be the maximum amount of current capable of being carried by either the red or the black wire  (both of which are rated at 20 amps and  both protected by 20 amp breakers). When both circuits are in use, the current carried by the white wire is not the sum of the current running through both wires, but the difference between the current running through them.   This is because the circuit with the lower amperage will always cancel its total from the larger leaving only the difference.

Cover over electrical box in back of pantry

Well, I didn’t want to mess with that, so, since the old microwave outlet was to get buried behind the new pantry once it the pantry was installed, I  terminated the wires in the box, cut a hole in the pantry cabinet back and installed a cover plate over the utility box in the back of the pantry  so that the wiring was accessible as required by code.  Then I ran a new dedicated circuit from an unused breaker in my breaker box to the position above the new microwave mounting location.

Soffit above microwave/range vent shown open for access to electrical, ducting and attachment points

I did want to vent the microwave oven vent to the outside which could be done through the ceiling and out the wall of the house in the attic space above the laundry room. Consequently, the traditional method of mounting the microwave oven/vent hood on a squat overhead cabinet and installing the outlet in the back of the cabinet wouldn’t work properly since vent would make the cabinet space almost unusable and the undisguised vent would be visible going through the ceiling above the cabinet.  I decided, instead,  to build a soffit under which the microwave/range vent could hang and which would obscure the vent and hide the electrical outlet powering the microwave from view.  Again, for reasons of code compliance this soffit needed to be able to be opened to get to the electrical.  It also needed to be able to be opened up in order to secure the microwave/range vent to the soffit.

Some useful web pages for a reader wanting to learn more about electrical wiring include:

Next time, I’ll discuss further electrical and wiring matters

That’s enough for now! Have fun!  Be safe!




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