You need to know how much current your theatre lighting can draw as the supply into your building is limited. This article will calculate the Maximum Power or Current that can be drawn by your dimmer rack(s). If you draw too much power you may trip a circuit breaker in your building or in a worst case situation you may blow a pole fuse in the street. Any of these scenarios will cause an interruption to your production!
If you want to increase the current into your building you will need to contact your electricity supplier to get a price and you may find that the street wiring may not be able to supply the current that you want.
In some instances it has proven cheaper to change to LED theatre lighting as it draws less power, it all depends on your budget.
A conventional theatre lantern has a lamp that has a Wattage rating on it. The smaller lights usually have 500Watts or 650 watts, the larger ones usually have 1000 Watts or 1200 Watts.
The calculate the current needed for each type of lamp, we need to use an ohms law power equation Power(Watts) = Voltage (Volts) x Current (Amps). If this is too difficult download a smartphone app such as Electrodroid or LD Tools.
Current in Amps = Power in Watts / Voltage in volts. The mains voltage in Western Australia is 240 volts, so for the common lamp sizes:
500W lamp uses 2.08 amps.
600W lamp uses 2.5 amps. Selecon Pacific Red base, Selecon Axial Acclaim zoom profile.
650W lamp uses 2.7 amps.
1000W lamp uses 4.16 amps.
1200W lamp uses 5.0 amps.
To identify theatre lights go to Theatrecrafts.com https://www.theatrecrafts.com/pages/home/archive/manufacturers/
A typical theatre lighting dimmer format in Australia is twelve channels of 2400 watts capacity which is 10 amps current. These twelve dimmer channels are usually grouped into three lots of four channels so they can be supplied with three phase power, four channels per phase, to reduce the size of the street wires feeding buildings. The typical dimmer will require 40 amps per phase or 120 amps total.
The above calculations are for a maximum current draw. If you only have one 650 watt lamp per channel, then a 12 channel dimmer rack will draw 12 x 2.7 amps which is 32.4 amps, a lot less that the maximum capacity of the dimmer which is 120 amps.
This method of having one theatre lamp per channel provides better control of your lighting, but requires discipline and an understanding of how to patch your theatre lighting.
Some community theatres have had smaller capacity 20 amp circuit breakers fitted to their dimmer three phase sockets to allow for more dimmer channels in total for what their building supply can accomodate.
If you do not have three phase power available you can have a technician convert your dimmer to three 15 amp single phase inputs by removing the common neutral to prevent tripping or RCD’s. You then have three 4 channel dimmers in a common case with a maximum current draw of 15 amps or 3600 watts shared between the four channels.
Page updated 7 July 2023