Sunday, January 27, 2008

Parallel Circuits

The wiring in your house is in parallel circuits. Here is another view of the 2 flashlight batteries wired in parallel (discussed earlier):

Let’s start with a description of a duplex outlet receptacle, commonly found in homes:

The neutral screws will be silver colored and the hot screws will be darker (sometimes gold). The grounding screw is green. On a quick-connect, use the holes that are just behind the slots.

Three outlets wired in parallel could look something like this:

Power enters on the black (hot) wire and leaves on the neutral (white) wire. It is important to keep the black (hot) wires to the hot (smaller slot) side of the outlets.

There are two screws on each terminal. They are joined by a tab, as long as the tab is intact; it makes no difference which screw you use on that side. If you break the tab, then the connection between the upper and lower “plug in” will be broken.

You will see why that can be useful a little later. Now let’s talk about switches. For simplicity, I will only mention single pole switches. I will devote a later discussion to other types of switches:

Here is basically what happens in a single pole switch. The two screws are connected
in the “ON” position. The connection is broken in the “OFF” position. The purpose of the single pole switch is to break the connection of the hot conductor. This interrupts the circuit and kills the power.

There are several ways to wire a switch in a 120 volt parallel circuit:

Power going to a switch is called the “feed”. Power going from the switch to a light, outlet, fan, etc. is called the “switch leg”. In this diagram, a switch controls a light. I have not used the ground conductors to keep it simple.

This same switch could just as easily control an outlet. This is often done at room entrances. A lamp can be turned on to light a dark room, upon entry.

The common screw (darker) will stay hot all the time. This is important so, power can be run to something else. If you ran additional things like outlets, from the switch leg side, everything in the circuit would be dead when the switch was “off”.

In this diagram, the light and outlet A are off. Outlet B is live.

In this diagram the switch operates the top plug of the outlet. The bottom remains hot all the time. Notice the tab broken. That separates power from the top and bottom.

At present, the top is dead and the bottom is live. To do this, you must run an extra hot wire. But in some cases, the switch and outlet are in the same box (double gang), so the extra wire need only be a few inches long.

When using switches, the neutral wires will need to be spliced together. The best thing to use is a spring loaded wire nut. They thread on the wires and work very well.

They come in many sizes. There is just the right size for the job you need. If splicing only 2 wires, there is no need to twist them together. Just strip about ½ inch of insulation.

If twisting the wires, you will need to strip quite a bit of insulation, then snip it off even. Make sure you snip enough so bare wire will not be showing, after you have threaded the wire nut on tight.

The green wire nut is for ground connections and no need to worry about bare wire showing.

Next is 240 volt circuits.

1 comment:

Unknown said...

THANK YOU, for what must be the only great diagram on parallel wiring outlets. This is how I had everything wired up, but wanted to just double check, and once I found your diagram, I kept reading for more great information to brush up my electrical 101.