Remember that electricity can kill you!! Before touching the main panel or any sub panels check them with a voltage tester to make sure that it's not electrified. Voltage testers can be purchased very inexpensively at a local hardware or electrical supply store. There was a story in a home inspection newsletter about one inspector who noticed that the insulation on the service entrance line had worn off at the top of the main panel. This caused the main panel to be electrified. Luckily he tested the panel before touching it.
Also, don't go near any exposed wiring or any electrical panels or wiring if there's water on the floor or near the wires. Water and electricity don't mix! You're not paid to get electrocuted; you're paid to inspect the house. State home inspection and appraisal standards state clearly that a home inspector and/or appraiser is not required to do anything that can be hazardous to themselves or to others.
Check the main panel for any rust or corrosion. If there's excessive rust or corrosion, then recommend that a licensed electrician evaluate the system. After testing the electrical panel with a voltage tester check to make sure it's installed on the wall securely by gently trying to shake the panel. Be careful - you don't want to loosen the electrical panel nor any wiring, you just want to see if it's secured properly. See if there are any hazardous conditions around the panel. Some hazards to watch out for are: potential water, objects in the way, the panel being too high to reach safely, etc.
Check to see whether the system has fuses or circuit breakers. Newer houses have circuit breakers which are the plastic switches that can easily be turned on or off by the homeowner. Older houses have fuses which are the glass screw-in type. Do not turn any circuit breakers on or off and do not replace any fuses!! Sometimes a circuit will be off because the homeowner is making repairs or the circuit was overloaded. Just inform the client of this and tell them to check with the owner or a licensed electrician to figure out the cause. You aren't allowed to turn any circuits on or off or replace any fuses for safety reasons.
If a circuit breaker is overloaded, it will "trip " into the off position. When this happens, no more electricity will travel to the outlets or switches on that branch line until the circuit breaker is moved back to the on position. If a fuse is overloaded, it will "blow." When this happens, no more electricity will go to the outlets or switches on that branch line until the fuse is replaced with a new one. A blown fuse will have a burnt color and the metal connector in the middle will be cut in half.
When a circuit is overloaded, it simply means that there was too much electricity being drawn on that particular branch line wire. As a result, the circuit breaker turned off or the fuse blew, if they were operating properly. This is how circuit breakers and fuses help to prevent electrical fires.
Electrical fires are caused by the fact that when electricity passes through a wire it creates heat. Each branch wire has a particular rating in amperage. The branch wiring goes from the main electrical panel to each outlet and switch on the individual branch circuits. Let's say, for example, that a branch wire is rated for 15 amps and the electrical current on that branch wire is drawn up to over 15 amps. If this happens, then the fuse should blow or the circuit breaker should turn off. This will help to prevent the current from heating up the wire so hot that it burns off the insulation and then starts a fire in the house.
If an electrical system has had past problems with overloaded circuits, the cause could be from many different factors. Some of the more common reasons are:
The electrical capacity entering the house is insufficient for the present demand due to the homeowner's electrical usage. They may be using too many window air-conditioners or electrical appliances and computers for the system to handle. If this is the case, then the system must be upgraded to provide more amps.
Another common reason is that there are too many outlets and/or switches on that particular branch line. More branch circuits will need to be installed to help cure this. This problem is similar to having a plumbing supply line that's supposed to carry water to one bathroom and instead it's going to two bathrooms. The water pressure will drop due to excess water being drawn from the supply line. This water pressure analogy is the same concept used with electrical currents.
A benefit to having circuit breakers is that when a circuit is overloaded, the homeowner only has to turn the breaker switch to the on position to restore the electrical current. However, the disadvantage is that if circuit breakers aren't tested occasionally, they can freeze in the on or off position which can be hazardous since it won't operate properly.
With a fuse system, if the circuit is overloaded, then the fuse has to be screwed out and replaced. Often there are no spare fuses to install. Also, with a fuse system you have to be very careful that you install the right size fuse for that particular branch line. Many times homeowners will install any spare fuse that they can find lying around. If a 30 amp rated fuse is installed on a 15 amp branch wire circuit, then the circuit wiring can be overloaded and cause a fire. The electrical draw on that line might exceed 15 amps but the fuse won't blow to stop the current because it's rated at 30 amps! One way to prevent this problem is to have a licensed electrician install a Fusestat. A Fusestat is a screw-in part that will restrict the size of the fuse for a particular branch line. This will help prevent, for example, a 30 amp fuse being installed on a 15 amp branch line.
Check the fuses or circuit breakers to see if they're marked to show where each branch circuit leads to. This is a convenience and safety feature. For instance, if the electrical power needs to be shut off to a particular room of the house, then the markings will help to identify which circuit breaker or fuse will need to be turned off. The markings will also assist the homeowner in case of an emergency or if repairs are needed. There is no way for you to decide if the circuits are properly marked for the location of their corresponding branch circuits. You would have to turn off each branch circuit and see what switches and outlets were turned off to try to determine this. However, you cannot turn any branch circuits on or off during a home inspection for safety reasons.
Check to see if there are any open circuit breaker or fuse slots in the main panel or any sub panels. Open slots need to be covered with blanks or spare circuit breakers or fuses. This will prevent anyone from sticking their fingers or objects in the panel and getting electrocuted.
See if there's any room in the main panel for additional branch circuits. This will be noted by having blanks or unused circuits in some of the slots. Any unused circuits will allow the homeowner to expand the system by adding more branch circuits directly from the main panel without having to install sub panels.
Sub panels are small electrical panels that branch off from the main electrical panel. The purpose of sub panels is to prevent very long branch circuit runs in the house. As electricity flows through the wires it'll begin to lose some of its current potential and there will be a "drop" in the electrical current. It's similar to the water pressure in plumbing systems. If the branch wire is very long, then the current at the end of the circuit won't be as strong as the current at the beginning. Sub panels help to prevent some of this current drop. Sub panels are also a convenience in that they allow the homeowner to reach the circuit breaker or fuse without having to go back to the main panel.