Atlantic Illumination Entertainment Lighting

AIEL Instructional

ALTERNATING CURRENT
ELECTRICAL POWER

Here is a short discussion of
alternating current (AC) power
and its cable as related to
stage lighting in Canada.


THE FOLLOWING MAY NOT BE REPRODUCED
WITHOUT PERMISSION FROM THE AUTHOR ©


  ELECTRICAL CONCERNS

    With some exceptions(*), all non-transformered stage lights
in Canada use lamps that are rated and tested at 120 volts AC.
Always use this voltage in your calculations:


The Power Law: P = I x E

    In electrical or physics terms this means: Power = Inductive Force times Electromotive Force. In more common language it means Power (Watts) = Current (Amperes) times Voltage. In very common terms remember: Watts = Amps x Volts. ( W = A x V )

    So to determine what current is drawn by 2000 watts of lights, use simple algebra to rework the formula. Divide 2000 watts by 120 volts to get 16.67 amps. Thus, a 20 amp circuit is required if you intend to turn on this many lights at the same time. (A 20 amp breaker or fuse is the next highest available above 16.67 amps.) Of course, you could have 10,000 watts of lights in your show, just don't turn on any more than 2400 watts, which is the maximum a 20 amp breaker can handle indefinitely. (20 amps x 120 volts = 2400 watts.)

    Be sure the circuit selected is free from such things as a vending machine or an audio system. Otherwise, you will only be able to consume the available power left over after those items have consumed their power. So if your audio equipment draws 15 amps at maximum output, that leaves you with 5 amps for lights. 5 A x 120 V = 600 watts.

(*) Some stage lighting lamps are now rated at 115 volts.
These will draw more current and consume more power at
120 volts. As an example, the popular 575-watt, 115-volt
lamps actually consume around 615 watts at 120 volts. Be
sure to take this into consideration when calculating
total current draw when running these lamps at 120 volts.


  DETERMINING CABLE SIZE

Extension cords must be used to plug in your lights.
Here is a chart to determine the size (wire gauge)
required when using Cabtire type of cable:


   Wire Gauge /      Suggested Maximum Wattage
    Number of              for up to a
   Conductors             30 Metre Run


        18/3                  750 W
        16/3                 1000 W
        14/3                 1500 W
        12/3                 2000 W
        10/3                 2500 W

Please note that these ratings are for 3 or 4 conductors
within a common jacket. They have been derated from the
maximum, as permitted by The Canadian Electrical Code, so
as to allow for up to a 30 metre run. The chart below shows
some main-power cable ratings:



  Wire Gauge & #    Suggested Maximum Wattage
  of Conductors       for Each Hot Conductor


      8/4               4,000 W
      6/4               6,000 W

     #4 Single         12,000 W  For Continuous
     #2 Single         24,000 W  Usage Beyond a
                                 15-Metre Run,
                                 Derate by 25%

    #4 and #2 are rated as single conductor cables; however, loosely binding 4 or 5 together for a main power feed does not change this as there is no heat-holding outer jacket. Note that not all cable types of this gauge can handle the wattages listed. Insulation material must be considered. Consult manufacturers' catalogues for their actual ratings.

    Voltage Drop: If too small a gauge is used for your current draw you will experience voltage drop at the end of the cable run. This will result in dimmer lights, or distorted audio if the latter is on the same cable. Also, heat will be generated, and over a period of time your cable insulation may break down, resulting in short circuits, melted connector housings, and a possible fire. So always determine your maximum current draw and use appropriate cable.

    Cable Types: Use rubber covered cable such as Cabtire Type SJ for up to #12, from there up to #6, use Type S, and for large main power feed cables we suggest Tech cable or Coleflex/Ultraflex types. Do not use plastic covered cables such as lawn mower extension cords. The plastic covering splits under heavy use, the moulded ends become loose in short order (especially the ground prong at the male end), and orange or yellow cables running around the stage are tacky and considered amateurish.

    Voltage Rating: Be sure the voltage rating is well above that being used. Remember that in Canada, end-user panel feeds will have 208 or 240 volts between some conductors, so use 300 volt or higher ratings. Higher ratings usually mean thicker insulation which also translates to more durability. Type SJ is rated at 300 volts while Type S is rated at 600 volts. Ultraflex is rated at 600 volts. Refer below for ideal voltages between conductors in Canada:


  VOLTAGES           Single Phase   Three Phase


 Hot to Hot:             240           208
 Hot to Neutral:         120           120
 Hot to Ground:          120           120
 Neutral to Ground:       0             0

    As just mentioned, these are ideal voltages, but you are likely to see a higher or lower voltage in most places. Do not exceed any more than 10% higher nor 15% lower. Voltage between neutral and ground is not good. Because they are connected together at the service entrance, they should theoretically be at the same potential.

    Voltage present between them is an indication of a poor connection of one or both, or of unequal, excessively long runs with a wire gauge that is too small for the intended purpose. In this situation, try to locate a better ground or neutral connection, if possible.


COLOUR CODING

This is standard Canadian colour
coding for AC electrical purposes:


GREEN:        Ground

WHITE:        Neutral

BLACK:        Hot

RED:          Hot

BLUE:         Hot

Please remember that voltages, cable types, and
colour coding in this article are for Canada. Other
countries have their own standards which may differ.



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