From a schematic layout, the electrical service is identical, it is only the physical attributes that have been updated, see Figure 2.

After passing through the main disconnect, switch with fuses or circuit breaker the electricity is sent to an electrical distribution panel (load center).

The distribution panel (load center) does exactly what its name implies – it divides up the power and distributes the electricity throughout your home utilizing a number of circuit breakers or fuses to protect each individual circuit.

Figure 2 - Drawing of a home electrical service

In North America, our consumption of electrical power within our homes has grown dramatically over the past 30 years.  Thirty years ago, a residential electrical service supplied 60 amps of electricity.  Today, small homes will have a 150 amp service, a medium size home will be supplied with a 200 amp service and larger homes or homes with on-demand (tankless) electrical hot water service will have a 400 amp service.

Similarly, the number of branch circuits that come from the distribution panel (load center) has grown.  The standard 60 amp fuse panel generally contained two plug in fuse holders, one for the stove and one for the hot water tank and six or eight circuits.  Today’s standard distribution panels will house 30 to 40 independent circuits and where 30 years ago, a kitchen was fed with one 15 amp circuit for all of the above counter receptacles and the refrigerator a new home will have a separate circuit for the refrigerator, a separate circuit for the microwave and each above counter receptacle will have its own 15 or 20 amp circuit.

The Electrical Service:

The electrical service coming into your home is a nominal 240 volts supplied as two 120 volt circuits 180 degrees out of phase.  Hence when added together you get 240 volts, see Figure 3.  The service is three wires, two 120 volt wires and one neutral wire. 

Figure 3 - 120 - 240 VAC electrical service

Continued........