Appliances and equipment that were traditionally very expensive have become relatively affordable, enabling more people to add central air conditioning, humidification systems, backup generators, and other equipment to their homes. Though the tendency is usually to get the system installed and running immediately, this can be a mistake. If electrical service capacity is not assessed before plugging in new equipment, irreversible damage may occur.

Electrical capacity is measured in amps and though determining it is not difficult, the process is dangerous. Visual inspection typically provides the answer, but this should be performed carefully. Service entry cables, the electric meter and meter base, main switch, and electrical service panel may need to be inspected and live electricity runs through these areas.

The question of how much electrical service is provided is answered by ampacity and voltage. In the United States, service voltage at the electrical panel is commonly 240 volts. This system will support both 120 and 240-volt circuits. Inspection begins at the electric masthead, where two 120-volt hot wires entering the structure provide both 120 and 240 volts. If electrical service was installed in the building before 1940, only 120 volts and 30 amps may be supported, though this is becoming obsolete.

Electrical capacity provided by a service entrance conductor is determined by identifying wire size. However, the main breaker and the panel size may establish a lower limit. Be aware that it is dangerous to inspect or touch an electrical component due to shock risk or death by electrocution. Before inspecting electrical equipment, learn safe electrical practices.

If available electrical capacity is sufficient to support the voltage of the equipment, plug the item into an electrical outlet. Look for indications of electrical circuit overload such as flickering lights or shutdown of power. If this occurs, turn off electrical supply at the circuit breaker box, unplug the equipment, and contact an electrician.