How an Electrical System Works

Utility Company Power Pole
Timothy Thiele

Everyone uses electricity in their homes every day, but how does it get there and how is it distributed throughout the home? For electricity to function properly, it must always complete a circuit.

Electricity flows in from one of two 120-volt wires and backs out through a grounded neutral wire. Any flaw in the wire to and from these points will interrupt the current’s path and cause a fault in one of your circuits.

Knowing how the power flows into your home, how it’s connected, and how it is distributed can help you isolate any problems that occur.

Service Entrance

The utility company’s overhead service lines feed the transformer to step down the voltage to feed your home. It then travels to the weather head (service head) which is attached to a conduit connected to a meter box. This assembly is attached with anchor bolts and straps to support the weight of the pipe and wire.

Two 120-volt wires and a grounded neutral wire feed the meter through the weather head. The utility company is responsible for power to the meter, and the homeowner takes it from there.

The service from the utility company to the meter is always live unless it comes and turns it off. If there appears to be a problem on their side of the meter, don’t hesitate to call the company to repair the problem. It has special equipment for just such repairs. Never attempt to work on their side of the meter, ever!

Service entrance to a transformer.
Timothy Thiele

Electric Meter

The electric meter is attached to the service entrance pipe and is usually to the side of your house. It may be attached to the utility company’s power pole also. It can be fed overhead or underground.

The meter is a watt measuring device supplied by the utility company to track each month’s power consumption. There are meters with numbered dials such as a watch on older models and new state-of-the-art digital meters that can be read right from the utility company’s office.

An electric meter mounted on a pole.
Timothy Thiele

Weatherproof Disconnect

In most cases, the utility company will require a weatherproof disconnect right after the meter connection. This is often referred to as a safety switch or service disconnect. This allows the homeowner to disconnect the power from the utility company from the outside of the house without having to get to the electrical panel.

A great reason for this would be a house fire. The fire department can kill the power from outside the home without entering the home. This allows them to spray water on fire without worrying about being electrocuted.

A weatherproof transformer disconnect box.
Timothy Thiele

Electrical Panel

Known as the electrical panel, breaker box, fuse box, or service panel, this piece of equipment is the next device in line. This panel’s job is to distribute power throughout your home and disconnect power from the incoming feed.

The power comes into the main breaker and is usually 100 or 200 amps. Individual breakers then distribute individual circuits (called branch circuits) throughout your home.

These breakers range in size from 15 to 100 amps. Lighting circuits would be 15 amps, outlet circuits would be 20 amps, and a sub-panel circuit to a garage or tool shed would usually be 60 or 100 amps.

An electrical panel mounted on the wall.
Timothy Thiele

Grounding Wire and Water Ground Connection

The service must be connected to a ground rod outside the house and also bonded around the water meter in the house. A jumper connected on both sides of the meter must be made to allow the meter to be removed without losing a ground connection.

Ground rod connection near rocks and foundation.
Timothy Thiele

Approved Electrical Boxes

The branch circuits are run into electrical boxes that are mounted inside of the walls of every room of your house. The National Electric Code requires that wires be spliced into boxes.

The reason is to make every connection accessible. For instance, if you splice the wires together and tape them within the wall cavities with no box and cover it with drywall, how will you get back to it to work on the splice if there’s a problem? You can open a box at any time.

An electrical box.
Timothy Thiele

Switches

Switches come in many different styles. There are single-pole, three-way, four-way, dimmer, and motion-sensing switches. Their purpose is to turn on and off a circuit from different places in your home. Switches are used to control lighting, ceiling fans, receptacles, and appliances. Switches have different amperage ratings depending on the load requirements.

Electrical switches side by side.
Tim Thiele

Receptacles

Receptacles, commonly referred to as outlets, are used to provide individual plug-in points for power distribution. The housing market most frequently uses 125-volt as well as 15- and 20-amp receptacles for general household equipment. For appliances such as 250-volt window air-conditioning units, a 250-volt 30-amp outlet is required.

Hopefully, having learned the basic parts of the electrical system will be useful to you in the future. Knowing how everything flows from start to finish helps in tracking down electrical problems that might arise.

An electrical receptacle.
Tim Thiele