Easy basic house wiring diagram for phones, doorbells, and security systems


Now, let’s take a look at the basic house wiring diagram for low voltage wiring which is used mainly in doorbells, residential phone systems, alarms, audio speakers, and intercom devices that also use low voltage wiring.


Most electrical contractors will install these communication lines, but due to the complexity of home wiring, many contractors leave communications wiring to residential phone services professionals.

Doorbell wiring ties in to the electric circuitry of your home by means of a transformer that reduces voltage. The transformer will fit into a junction box just like a light or a switch.

The illustration below shows a doorbell controlled from two locations. Usually the chime is different between the front and back so you know which door to answer.


The 120-volt line goes into the transformer and usually two small lines go to each doorbell. The wires are usually about 18-guage and carry a voltage smaller than 12-volts.

doorbell wiring

The phone system is another low voltage line, except it isn’t tied in to the electric circuitry of the home. The voltage comes from the phone company and is maintained by them. They will install service up to the box. This box is called a “Demarcation block” or just “D-marc block”.

To us homebuilders, it’s just a box. From the box, we run our separate lines to each modular jack or phone jack. If you have multiple lines, you will have to map out a circuitry route just like the electrical circuits so you don’t get confused. A basic-house-wiring-diagram for simple phone systems will be fine. The modular jacks will fit into regular electric boxes.

The illustration below shows a simple residential phone system with two phone lines. The phone company only runs service to the box.

The homeowner then runs the wiring from the box, into the house, and on to the rooms in the house that will have phones in them. The illustration is an example of a “Daisy chain” wiring method.

This is an old way of doing things. The problem with a daisy chain is if one phone jack goes bad, all the ones behind it will stop working.

phone wiring diagram



A solution to this problem is called a “junction box”, or a “star”. It acts like a hub and each mod jack or phone jack will be wired separately and exclusively back to the junction box. It takes more cable, but is more reliable. The illustration below shows an electrical wiring diagram for residential phone systems.

residential phone wiring



Now that we can see how the circuit is laid out, we need to know what kind of cable to use. The most popular cable being used in residential as well as commercial dwellings is called “CAT 5” cabling.

It stands for Category 5 cable, which was mostly used in network wiring because of its high data transfer capabilities, but was too expensive for home use.

Now, it’s more reasonable in price and it is better for homes or businesses that will someday be expanding their communication needs. That is most of us if you consider the impact that computers have had on our communications systems over the past two decades.

Besides, appraisers love to see “Data ports” in every room. It just says, “ I’m a modern, state-of-the-art home and I’m built with the future in mind”. That will boost the home’s value by thousands. No kidding.

Cat 5 cable is a plastic shielded cable with four twisted pairs of color-coded wires.

phone jack wiring



The CAT5 cable is run just like the other basic house wiring diagram electrical circuits. The cable will run to each room that will have a phone and it will have an outlet in the form of a wall plate or a flush mount mod jack.

The cable will be wired to the RJ11 outlet or mod jack using the red-to-red, and green-to-green wires for the first line, and yellow-to-yellow, and black-to-black wires if you’re using regular phone cable.

Just as a side note here, the CAT5 has eight cables, but not all wires need to be used. In fact, you only need two wires for each line, so as a rule of thumb you start out using the red and green wires or whatever color is close to those colors that you can remember.

I say that because CAT5 varies in colors from manufacturer to manufacturer. The standard for wiring also varies between phone companies so you will get many different answers if you want the right one.

The right answer is just this: be sure to use the same wiring order on both ends of the cable so that the phone lines actually work. You will want to use the same standard throughout the entire wiring though, that only makes sense.

Now, having said that, I will say that there is a vague industry standard that helps maintain some form of compatibility between old and new cable.

phone system



The phone company uses 8-wire cable, and many residential dwellings still use 4-wire cable. There might be certain local codes about which colors of wires go where, but they aren’t strict like electrical codes.

If you decide to take advantage of the wiring diagram star idea instead of the daisy chain method, there will be one line of CAT5 that runs from the Telco box to the junction box. Just remember to have one line coming in from Telco, and then you can connect several mod jacks running from the hub.

phone circuit wiring diagram



This is a phone system hub where a phone lines comes in from telco and it feeds different phones throughout the house. Each phone line will have a separate hub. Most homes are wired for multiple phone lines.

phone system wiring



An important note about the basic house wiring diagram for phone lines is the use of CAT5 cable. Almost all brands of CAT5 cable are somewhat mouse and vermin proof.

You don't want to have to be digging into the walls to fix a cable that was chewed in half.

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