The electrical service in most American commercial buildings is what's called "three-phase"; into every power box are run three "hot" wires, one neutral wire, and a safety ground. The voltage measured (don't do this yourself) between any two hot wires is approximately 208V. The voltage measured between any one of the hots and the neutral is nominally 120V (but usually somewhere between 110V and 125V). There should be no measurable voltage between the neutral and the ground. This power is "branched off" to individual circuits, each one (except in the case of units such as air conditioners and other large motors) having one hot, the neutral, and the ground, therefore being 120V.

The electrical cables which are approved for use in theatres typically contain three wires: black, white, and green. The black wire is the hot. The white wire is the neutral. The green wire is the safety ground.

The path by which electricity gets from the dimmer to the lighting fixture is this:

"AWG" stands for "American Wire Gauge" and is a measure of the diameter of an electrical conductor; the lower the gauge, the larger the wire. Note that the "0" is pronounced, "aught," so that "0000" is referred to as "four-aught".

The National Electrical Code mandates that cable used in theatres be "jacketed" (having an outer insulation around the individually-insulated inner conductors), stranded (as opposed to each conductor's being a solid piece of copper), and rated for "hard" service. The standard cable used in American theatre is 12AWG Type SO (The "O" stands for "oil resistant"). For certain uses (for example, twofers), type SJ or SJO (the "J" stands for "Junior" service. The insulation on type SJ or type SJO cable is not as robust as that on type SO cable) may be used.

In America, most dimmers are rated for 20 amps, so by the table, you should use #12 cable with those dimmers. The connectors on those cables also need to be rated for 20 amps.

Stage Pin (also known as "2P&G," "GPC," or "two-pin and ground") This is the connector found in most professional theaters and on the equipment provided by most rental houses.
Twistlock
Parallel Blade (also known as "Edison," "PBG," or "Household")

There are two types of twistlock connectors in common use in North America:

The "Non-NEMA" type has the bend in the "ground" pin facing away from the center of the connector. It is obsolete and illegal to use in new construction. It is typically rated for multiple voltages.	The "L5" type has the bend in the "ground" pin facing toward the center of the connector. The L5 connector is rated for 125V, the voltage most commonly used in North America. It is similar in appearance to, but not compatible with, the "L6" connector, which is rated for 250V. North American theaters using twistlock connectors most often use the L5-20, which is rated for 20 amps at 125 volts.

Even though the stage pin is not a locking connector – especially because it is not a locking connector – it's important to make sure you have a secure connection when plugging in a fixture or connecting two cables. The connectors should fit snugly together; if they do not, one (or more) pin has become compressed.

As you can see in the photograph above, each pin has a slot down its length. Inserting, carefully, a pin spreader (available from most theatrical suppliers) will decompress the pin and guarantee a reliable connection, both mechanically and electrically.

Each type of connector has its advantages and disadvantages:

On a stage pin connector, the ground (green) conductor is attached to the middle pin. The neutral (white) is the pin closer to the ground, and the far pin is the hot (black). Notice that the ground pin is slightly longer than the others, so that it is the first to connect and the last to disconnect.

"Best practice", no matter which type of connector, mandates that the conductors be connected in this order:

• Ground
• Neutral
• Hot

When wiring connectors (of any type), make sure that the strain relief securely grabs the outer insulation or "jacket", so as not to place undue stress on the individual conductors.