Appendix
February 16, 2010
-29-
COLORado™ 1 Tour User Manual Rev. 01f
Sizing the
Circuit
Breakers
Calculating the total current drawn by the fixtures connected to a particular circuit is not
complicated if the installer has the right information at hand and knows how to interpret
it.
With the fixture’s current draw information, the installer can calculate and select the
right circuit breaker size (rating) to which they can connect a group of fixtures.
Using the
Spec Sticker
CHAUVET® fixtures come with a sticker that indicates the current they consume in a
circuit at the specified voltage. This greatly simplifies calculating the total current
drawn.
For instance, if the sticker on the fixture indicates, “0.1 A @ 115 VAC, 60 Hz” and the
installer is connecting 12 of them on the same 115 VAC circuit, to determine the total
current required by the fixtures it would be enough to do this simple calculation:
0.1 A x 12 = 1.2 A
Using the
Watts/Volts Method
Some installers may prefer to determine the current drawn by the fixture by dividing its
power consumption, indicated in watts (W), by the voltage (V) on the circuit. As an
example, assuming that a certain fixture consumes 240 W and it is connected to a 120
VAC circuit, the current it draws would be:
240 W / 120 V = 2 A
Considering the
Power Factor
The above method is accurate only with fixtures whose power factor (PF) is equal, or
very close, to “1.” Otherwise, the calculated current may be too low with respect to the
actual current drawn by the fixture.
In fact, as the PF decreases, the difference between the current calculated using the
watts/volts method and the actual current increases.
Therefore, for fixtures with a PF below “0.9,” the installer must always consider the
fixture’s PF when using the watts figure to calculate the current it draws.
For the above example, if the published fixture’s PF were “0.7”, the resulting drawn
current would be as follows:
2 A / 0.7 = 2.8571 A
This is approximately equal (
≈) to 2.86 A, 2.9 A, or even 3 A, depending on the
installer’s desire for accuracy. In other words, the actual current ended up being close
to 50% higher than originally calculated.
Using the
Volt Amps Method
If the fixture’s sticker indicates the power consumption in “volt amps” (VA), the
calculation of the drawn current is simply the result of dividing the amount in VA by the
voltage on the circuit (V). For a fixture with a consumption of 360 VA, the calculation
would be as follows:
360 VA / 120 V = 3 A
Note that when the power consumption is in VA, the fixture’s PF is never part of the
current draw calculation.
Selecting the
Circuit Breaker
The National Electric Code (NEC) determines that circuit breakers should handle 80%
of their rated capacity for continuous loads (those being on for three or more hours)
and 100% for intermittent loads. For safety reasons, CHAUVET® recommends
assuming that all loads are continuous.
After calculating the total current the fixtures connected to a particular circuit will draw,
the installer must consider the 80% rule indicated above. For a total current of 22 A, the
calculation is as follows:
22 A * 1.25 = 27.5 A
The installer should use a 30 A CB because the immediately lower CB rating, 25 A,
would not be enough for this load.
