Ampere (A)

The movement or the flow of electrons is called current. Current is represented by the letter symbol I. The basic unit in which current is measured is ampere (A).

Electricity can be termed as electric current; which means the bigger the current, the bigger the wire size and breakers. (Amperes or current is often compared to water current; so the more water flows, the bigger the waterbed or pipe needs to be.) It is important to follow the electrical code on wire sizing to avoid overheating of the electrical equipment. In electrical panels, bigger wire diameters can help keep temperature low inside the panels. Low temperatures increases efficiency for electrical equipment, especially for thermistor's which are mounted in solid state relays (SSR and SCR).

For example 15 amperes require a copper wire size of 14; 130 amperes require a copper wire size of 1.

A 120V line in a household is usually protected by a 16A or 20 A breaker. With Ohm's law we can determine what the highest wattage is that we can connect to this 120V.

Formula: watts = volts x ampere
= 120 x 20
= 2400 Watts

Note: Adding a 25% safety margin, this 16A or 20A allows connecting a comfort heater to 120V, but would not allow connecting a moderately sized water heater which typically requires 4,000 to 6,000 Watts. (Remember: watts divided by volts equals amps)
Industrial plants have usually higher voltage and 3-phase available to satisfy their power needs.