Last Updated 29 minutes ago
Filmmaking Dictionary: Number 1 / 120 V (North American Mains Power)
Definition
120 V is a nominal AC supply voltage commonly found at ordinary receptacles in North America. The value describes electrical potential difference; it does not state the available current, total circuit capacity or the suitability of an outlet for a particular lighting setup.
Film productions may also use other supply voltages and distribution arrangements. Check the actual supply and equipment requirements rather than assuming that every familiar-looking connector delivers the same power.
Voltage, Current and Power
Voltage is measured in volts, current in amperes and real power in watts. For a simple resistive load, power is approximately voltage multiplied by current. An ideal 600-watt resistive load at 120 volts would therefore draw about 5 amperes.
Electronic lighting equipment can have power-factor behaviour, startup current and input requirements that make the simple division incomplete. Use the fixture or power supply’s electrical ratings and the production electrician’s assessment when planning the actual load.
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An Outlet Is Not Necessarily a Separate Circuit
Several receptacles can share one branch circuit, including outlets in different parts of a room or location. Plugging lights into different sockets does not prove that their combined load has been separated.
Existing appliances, building services and other production equipment may already use that circuit. The gaffer and electrical crew need an accurate understanding of the supply before assigning loads.
What to Check
- The equipment’s accepted input voltage and frequency.
- The identified circuit and its existing loads.
- The condition and suitability of cables, connectors and distribution.
- Grounding and required ground-fault protection.
- Cable length, routing and protection from damage.
- The requirements for the location and working conditions.
Wet conditions, damaged insulation or an unsuitable extension cable cannot be made acceptable merely because the connected fixture has a low wattage. Keep protective devices in place and have faults assessed by qualified electrical personnel.
Example During a Location Scout
A production plans several lights in an office. Instead of dividing the fixtures among nearby outlets by appearance, the electrical crew identifies the available circuits and checks existing loads. The lighting plan is then matched to the verified supply, with appropriate distribution and protection.
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Frequently Asked Questions
Does 120 V mean the circuit can supply 120 amps?
No. Voltage and current are different quantities.
Can I determine a safe load from voltage alone?
No. Circuit ratings, load type, wiring, protection, equipment instructions and applicable requirements all matter.
Should a breaker be bypassed if it keeps tripping?
No. Stop and have the cause investigated. A protective device is not an obstacle to work around.
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