About Your Home's Wiring
The Electric Utility Company
The utility company owns and maintains all of the wire and equipment up to the point of attachment to the customer's service cable. When the utility supplies power from underground, a different set of rules applies.
Service Drop
The service drop is the set of wires that leads from the utility connection to the meter. This is usually a heavy cable jacketed to withstand weather and sun. The service drop cable, like other parts of the service, is sized by your electrician according to the electrical loads in the house. Many homes can be adequately served by 100 amps, others may need more. Today's code specifies a minimum of 100 amps, though.
The service drop cable is often the first indicator that a service needs to be replaced. Exposure to the elements will eventually wear away the jacket and expose the wires inside to water. This can lead to dangerous damage to other parts of the service! A damaged service cable should always be replaced - a jacket can not be reliably repaired.
The service also includes an enclosure for a meter so the utility company can measure your power usage for billing. While the homeowner is responsible for furnishing and maintaining the enclosure, the utility company provides and owns the actual meter.
Panel Box
The panel box, or service panel, is where electricity is distributed throughout the house. Panels should have a main breaker or fuse. The main can shut off all current to the house at once when it is operated by hand or automatically when excessive current flows through the panel box.
Most panels also provide space for circuit breakers or fuses that supply current to circuits in the house. Fuses and circuit breakers provide critical safety to wiring. As more electric current flows through a wire, the wire's temperature increases. If there were no 'safety valve', the wire would become dangerously hot, and could start a fire. A circuit breaker shuts the current off automatically when its limit is reached. Electricians select circuit breakers to protect connected wires. While fuses perform the same basic function, their screw-in bases are the same. This allows a fuse set for 30 amps to be mistakenly installed into a socket connected to a 15 amp wire. In this case, the connected wire will get dangerously hot before the fuse blows, and a fire could be the result.
One of the most common homeowner errors is to replace a blown fuse with a new, higher rated fuse. When the fuse no longer blows as often, there is a mistaken belief that the "problem" has been fixed. Because of this, some home insurers are no longer writing fire insurance policies for homes that use fuses.
To deal with the problem, manufacturers have developed the 'S-type' fuse that involves the use of differently sized adapters that are first installed into the fuse locations. Once installed, only fuses of matching size can be installed into each position. From a practical standpoint, it is better to replace the panel with newer equipment that is larger and can accommodate more circuits.
The panel box also provides an attachment for grounding. All services should be connected to the cold water piping and to a secondary ground connection (often a rod driven into the earth) to provide a lightening discharge path.
Branch Circuits
Branch circuits are the wires that connect to things that use electricity in the house. Most branch circuits supply more than one outlet; lights and receptacles throughout the house are often connected by a chain of wiring that starts at a circuit breaker in the panel and connects to one outlet after another. The installing electrician uses the code and his judgement to decide what and how many things to put on a branch circuit.
In residences, most lighting and receptacles are connected to 15A circuits; heavier 20A circuits are installed for kitchen, laundry, and bathroom receptacles.
Some branch circuits, on the other hand, are dedicated to a single item. An electric range or water heater are examples of appliances that would be served by a dedicated branch circuit. Sometimes a dedicated branch circuit is installed to isolate a critical appliance from other loads. Refrigerators and freezers are often separated from other appliances for this reason.
The electrical systems in many older homes were not designed to provide for today's electrical use. Fewer branch circuits were installed than would be wired in a modern home. As a consequence, circuits are more often overloaded. A good repair would be to have additional branch circuits installed, particularly to large appliance loads. This helps by dividing the loads among more wires.
Branch Circuit Grounding
Older branch circuit wiring often does not include a ground conductor. Most people are familiar with a grounding conductor as the nuisance "third prong" on the power cord that won't mate with the two prong receptacle they are trying to use. Actually, such 'equipment grounding' provides protection from electrical shock. The ground connection is attached to a wire from the panel to create a safe zero volt reference. All metal parts in an electrical system that a person could touch are connected to this zero volt point. The adapters that many people use to connect grounding plugs to two-prong outlets can not provide a ground connection if there is no ground in the electrical box.

Computers and surge suppressing power strips use the ground connection for other reasons. Sensitive electronics are often protected from static electricity by a grounded shield. Surge suppressors protect sensitive electronic equipment by directing harmful electric pulses into the ground connection. In either case, connecting expensive electronic equipment to ungrounded circuits can cause erratic operation and premature component failures.
Federal Pacific Panels