When you're hanging lights you need to determine how many instruments you can put on a dimmer. To do this you need to use the power formula, W = V A, also known as the "West Virgina" formula.
To use this formula, you first need to determine the Amp rating of your circuit by looking on the circuit breakers on the dimmer pack (they are often 20A, but sometimes 15A). If you are using portable dimmers, you also need to know the Amp rating of the circuit breakers in the electrical panel and you need to know that nothing else is on that circuit. In addition to the dimmer/breaker, you also need to determine the Amp rating of all the cables and connectors you are using. You are limited by the component in the circuit with the lowest Amp rating. Take that lowest Amp rating and multiply it by the standard Voltage in the US, which is 120V. The outcome of that equation will tell you the maximum number of Watts you can put on the circuit.
For example, in Wood-Mar the dimmers are 20A. Since we know the standard Voltage is 120V, then we know we have 2400W available for each dimmer. 20A x 120V = 2400W
You'll then need to determine how many Watts are used by each lighting instrument, which should be listed on the lamp. Source Fours use 575W, PAR 64s use 1000W. So you could put four Source Fours on one circuit. Or you could put two Par 64s on one circuit.
Most of the time this is pretty straight forward, especially since most of the time we like to control only one light per dimmer. Where it gets tricky is in non-theatre spaces like a cafe, a community center, or a church. The hard part in those situations is identifying how many circuits you have available and what the Amp rating is for each of those circuits. Be careful! Multiple electrical receptacles in the room may all be on the same circuit, so you need to locate the electrical panel and find out which breakers or fuses operate which receptacles, and at how many Amps. In this kind of a touring situation, even though you may be using 20A theatre dimmers, you may be limited by the available circuits/Amps the dimmers are plugged into. For example, the portable dimmer packs in the Design Lab contain four dimmers in each pack which is plugged into one 20A circuit - so you must divide the available 2400W among the 4 dimmers. Each dimmer in the pack is capable of handling 1200W, but you can place no more than 2400W on the entire pack.
