In the theatre, as in most of the rest of modern life, electric power is used to energize equipment. It is the responsibility of every stagehand to understand basic electrical theory in order to safely work around electrically powered equipment.
Basic Electrical Theory
Electric charge is the physical property of matter that causes it to experience a force when physically in close proximity to other electrically charged matter. Subatomic particles called protons carry a positive charge, while particles called electrons carry a negative charge. Like-charged objects (i.e. positive + positive) repel each other, while oppositely-charged objects (positive + negative) attract each other.
Electric current is the flow of electric charge along a conductor (i.e. copper wire, like an extension cord). This is how we utilize electric power, or the use of electricity to energize equipment.
A basic electric circuit requires a power source (voltage), a conductor (hot wire) running from the voltage to the load (in our case, equipment to be powered), and a second conductor (neutral) running from the load back to the power source. For example, to power a Genie lift, we need a power supply (wall outlet), two conductors (extension cord), and the load itself (Genie lift).
Conductors allow electric current to flow through them. Insulators, such as rubber, inhibit the flow of electric current and are used in the jacketing around the individual wires in electrical cable.
Electric shock occurs when a person (in contact with the ground) becomes part of an electric circuit by coming in contact with a live electric circuit. Current from the live circuit will enter the body via whichever part of the body contacts the live circuit, and the current will pass through the body to exit to the ground (if standing on a conductive lift or ladder, the current will pass through the feet to the lift or ladder and then to the ground).
Three major factors govern the severity of electric shock:
- The amperage, or amount, of current traveling through the body.
- The path of the current traveling through the body.
- The length of time the body is in contact with the live circuit.
Most normal electric circuits in the United States are capable of providing 20 amperes (20,000 milliamperes) of electric current. The following is a list of effects of electric shock at varying currents:
- At 1 milliampere, a person can just barely perceive electric shock.
- At 5 milliamperes, shock is not painful, but perceptible and uncomfortable.
- At 6 – 30 milliamperes, electric shock is painful.
- Above 30 milliamperes, the affected person’s muscles may contract to the point where the person is not capable of letting go of the live circuit.
- At 50 – 150 milliamperes, breathing is affected, severe muscular contraction occurs, and the affected person will be in severe pain.
- Between 1000 and 4000 milliamperes, the affected person’s heart will suffer fibrillation, or rapid, irregular contractions.
- Above 10,000 milliamperes, the affected person will suffer cardiac arrest, severe burns, and probable death.
Treating Electric Shock
- If you see a victim of electric shock, do not touch them. Touching a person suffering electric shock will cause you to become part of the live circuit as well, and you will not be able to assist. Do not touch the source of electric current.
- Break the current. Shut off the power at the breaker panel if possible. If not possible, use a non-conductive item (made of wood) such as a broomstick or stick of lumber to move the victim away from the source of the current. If the victim is holding a wire or other conductor, attempt to use the wooden object to knock the victim’s hand free.
- Call P-Safe at 4-3333. Tell the operator that the victim is suffering from electric shock, and request that they respond with an AED (Automatic External Defibrillator). If you have not been able to remove or de-energize the source of electricity, warn the operator of this fact and follow the operator’s instructions.
- If the victim is unconscious, check for breathing and pulse. If the victim is not breathing, trained personnel should begin rescue breathing.
- Do not move the victim.
- Cover the victim in a blanket, remain with victim until help arrives.
Preventing Electrical Hazards
All theatrical wiring should be grounded or double-insulated to prevent fraying and wear on cable jackets leading to shock hazards.
- Cable which is grounded has three conductors instead of two.
- Most cable used in the theatre is double-insulated (typically with a black or orange outer jacket, and internal conductors are separately insulated). An example of single-insulated cable is zipcord, or lamp cord, which consists of two single-insulated wires running side by side. This type of cable is very vulnerable to wear or fraying of the outer jacket, which will expose conductors and present a shock hazard.
Extension cords are used extensively backstage. Some guidelines for the safe use of extension cords and cabling:
- Always use 3-conductor cable that is 16 AWG (American Wire Gauge) or smaller. Smaller AWG numbers indicate larger cable, which can handle larger amounts of current safely. Pulling too much current through a thin, light-duty extension cord can cause the insulation and jacketing of the cable to overheat and potentially ignite.
- Never pull extension cords apart (or out of outlets) by pulling on the cable itself. This can cause internal conductors or connections to part and potentially short circuit, or contact each other, causing the extension cord to fail. Always disconnect extension cords by pulling on the connector itself.
- Always inspect extension cords for fraying, splits, or bad plugs prior to use. Cable with exposed inner jacketing or exposed wire is an electrical shock hazard and should be removed from service, clearly marked with tape and a label, and reported to a supervisor.
- Never roll equipment over extension cords or any type of cable. The pressure exerted can cause internal conductors to part or can damage the jacketing, exposing the conductors and creating an electrical shock hazard. Lift cables up and roll equipment underneath, or unplug the cable and move it out of the way before rolling equipment past.
- Improperly routed extension cords can be trip hazards. Route extension cords around high-traffic areas to prevent tripping and falls.
- Do not pinch or stretch extension cords, as this can result in breakage of the conductors.
- When extension cords or other cabling are run across traffic pathways, they must be enclosed in cable protectors available from your supervisor or the Lighting and Sound Supervisor.
Training in electrical safety is available from the Lighting and Sound Shop Supervisor. Electrical safety training is mandatory for all members of Electrics and Sound crews and is administered by the Master Electrician during the crew training period.
In the course of your work, you may occasionally come across a piece of equipment, circuit breaker, or power cord which is padlocked and tagged to prevent its being turned on while it is being serviced. This is known as lockout/tagout.
- All lockout/tagout procedures will be undertaken by the Lighting and Sound Supervisor or the Scene Shop Supervisor.
- NEVER attempt to remove a locked out/tagged out object. Never attempt to circumvent it, as you may injure personnel working on the locked out/tagged out object.
- For questions on lockout/tagout, refer to the featured document on the right side of this page.
- When working with or near electricity, it is a good idea to invest in protective footwear which is shock resistant. In the event of accidental contact with a live electric circuit, shock resistant shoes increase the resistance of the body to electric current and decrease the current actually passing through the body.
- Rubber-handled tools are not sufficient to protect the user from electric shock unless they are clearly marked as 1000V Rated.
- Never work on or near live electricity alone – always have someone to watch out for you in case of emergency.
- Never keep food or drink near any live electricity or controls for electricity.