Electrical System photos: P 69-P 90, P 207
The National Electric Code, or the NEC as it's also called, is the standard that most local building departments use to draw up their electrical construction codes. Most local municipalities will adapt the NEC codes to fit the needs of their local area. The NEC codes are only recommendations and the local building departments are not required to follow them. However, the local electrical codes are never far off from the NEC codes because they're very good, safe recommendations.
The basic operation of an electrical system is very similar to that of a plumbing system:
Electricity is brought in through the service entrance lines to the house from the utility company lines in the street. It's just like a water main line.
From this main line, the electricity then passes through an electrical meter. The electrical meter registers the amount of electricity that's used. The electricity then travels to the main electrical panel.
From the main panel the current is then carried to different parts of the house. The current travels through the "hot " interior electrical wiring that branches out in different directions to all parts of the house. The hot wires are similar to the plumbing supply lines. The expression "hot" is used to describe the wires that are carrying the live electrical current to the appliance, outlet, switch, etc.
After the electricity is used at an outlet or light fixture, the used electrons then go back to the main panel along the "neutral" wiring in the branch lines. The neutral wiring is similar to the plumbing drainage lines.
Just as water in a drainage line is under extremely low gravity pressure, so the electrons flowing through the neutral wire are at close to zero volts. They've given up nearly all of their energy in operating whatever device they've passed through.
The neutral wiring then carries the neutral electron current back to the ground via the grounding cable. It's similar to a city or septic sewer system where the used water drains into.
There are three terms to describe the power of electricity: Volts, Amps and Watts.
The total of the electrical current is called Volts. For example, the total potential of the electrical current in a house with three service entrance lines, is 220 volts. This is similar to the water pressure in the water main line supplying a house. Let's say you cut open that main water line that runs from the street to the house. Then the amount of water pressure rushing out of this pipe would be similar to the potential of the current in the electrical service lines. The only difference is that instead of measuring the electrical current in water pressure standards, you're measuring it in Volts.
The total of the electrical current being used by a particular electrical branch line inside the house is called Amps. This is similar to the water pressure in the water supply lines inside a house. If you turn on a faucet, you don't draw all of the water from the water main line supplying the house. You just draw some of the water. The only difference here again is that instead of measuring the electrical current in water pressure standards, you're measuring it in Amps for that particular branch line. Amps is the abbreviation for Amperes. Amperes measures the rate or strength of electric flow. This is similar to the flow of water being measured in gallons per minute. Amperage is the actual measure of current flowing in a circuit to an appliance.
The actual electrical power being used by a particular light bulb or appliance inside the house is called Watts. The only difference is that instead of measuring the electrical current in water gallons per minute standards, you're measuring it in Watts.
You're not required to do any math but if you want to use mathematical equations to impress your client, then feel free. You can use the following equations to help figure out if there are any possible overloaded electrical circuits in the house.
Watts = Volts x Amps
Amps = Watts / Volts
The main components of the electrical system consist of: the service entrance lines, the electrical conduit lines, the electrical meter, the main electrical panel and any sub panels, fuses or circuit breakers, the interior electrical wiring and the electrical system grounding cable.
The service entrance lines are the electrical wires carrying the electricity from the utility company wires in the street to the house. These lines are usually overhead lines and are visible from the exterior of the house. However, some installations are underground and aren't visible. Underground installations have a smaller chance of damage due to bad weather or power outages due to falling tree branches.
Check the overhead service lines to make sure that there aren't any tree branches near the wires that can cause damage. All trees should be pruned away for safety. Make sure the lines are high enough off the ground to prevent a car or truck from hitting them.
Look at the service entrance head. This is the area where the service entrance lines attach to the exterior of the house. Make sure there's no rust or corrosion. You should use binoculars for this if it's too high to view clearly. Do not use a ladder to view the service entrance head!! It could slip and touch the electrical wires. You're being paid to inspect the house, not get yourself killed.
Check for the presence of a drip loop. A drip loop is slack in the wiring that's in a U shape. This helps prevent rainwater from following the electrical lines down into the main panel. If the U is installed, then the rain water will drip off the loop and onto the ground before entering the electrical conduit. That's why it's called a drip loop.
If there are only two service entrance lines going into the house, then there's 110 volts inside. If there are three service entrance lines, then there's 220 volts.
The service entrance head area will allow you to determine what the voltage is in the house electrical system. If there are only two service entrance lines going into the house, then there's 110 volts inside. A 110 volt electrical system will usually only have a maximum of 30-60 amps of electrical service in the main panel. If there are three service entrance lines, then there's 220 volts. A 220 volt electrical system can have up to a 200 amp electrical service in the main panel. On commercial buildings you'll find three service entrance lines that are much heavier gauge wires than those used for residential electrical systems. The commercial systems can have much more than 220 volts of power.
One of the service entrance lines leading to the house will usually be uninsulated. This wire is the grounding wire. The other line or lines carry 110 volts each. If there are three lines, then that's how you decide the house has 220 volts. Three lines prove the existence of two 110 volt service wires plus the neutral wire. Without getting into the intricacies of electrical current, each 110 line carries its current on a different phase. But for a home inspection you only need to figure out if the house has 110 or 220 volts.
Traveling from the service entrance head to the main electrical panel, the exposed service entrance lines should be enclosed in a conduit. A conduit is merely a covering to protect the electrical lines from the weather and damage. The conduit can consist of metal piping or a strong plastic insulator. Check the condition of the conduit to make sure there aren't any cracked or open areas and that all joints are sealed properly. The conduit will carry the service lines to the electrical meter. The location of the meter can be either inside the house or on the exterior. If the meter is on the exterior, then the utility company can take a reading without having to enter the house. In condominium buildings the meters for many of the individual units are usually located in one central area. This can be either in the lower level area or on the side of the exterior of the building.
You'll see moving parts inside the meter if any electrical appliances or outlets are being used inside the house. This is how the meter registers usage. Its operation is similar to a water or gas meter. Check to make sure that the caulking is in good condition where the electrical conduit enters the meter. This is important to prevent rust due to water entering the meter and flowing down into the main electrical panel. From the meter the conduit will carry the electrical lines to the main electrical panel. If the house has an underground service entrance line installation, then you'll see the conduit entering the main panel from the bottom, as opposed to the top. The main panel is usually located in the lower level or the garage.