American Cinematographer - March 2018 - 16

Andrew
Lesnie, ASC,
ACS shines a
light on the
2007 feature
I Am Legend.

Keeping the Lights On
By Jay Holben

Shooting on location, especially in the independent production world, often means that you're using "house power" - and
without a generator or a controlled electrical source, you're at the
mercy of how the location is wired and whatever preexisting load
there might already be on that electrical system. So let's talk about
techniques for making sure that you don't blow breakers or fuses
when you're using existing location power.
One quick aside: We will not be discussing "tie-ins," a
dangerous and controversial practice that, in some areas, is either illegal or must be done by a certified electrician. In general, it is not a
practice that I recommend.
Whenever you're using motion-picture equipment in a practical location, there is a concern about power consumption. Especially with today's technology and sensitive computer equipment,
one blown breaker can mean a major hassle for the location owner
and a black mark for you. But understanding how to keep the lights
on is not hard. It requires a basic understanding of electricity - and
just a little math. I promise, though, to keep the math as simple as
possible.
To begin, let's familiarize ourselves with the three main
components of electricity: volts, amps and watts.
To better understand these components' relationship and
what each one represents, I like to use an analogy. Imagine a large
bucket filled with water, with a spigot at the bottom of the bucket
to drain the water - this is the beginning of an electrical flow. If that
bucket has barely any water in it, we'll only get a trickle of water out
16

March 2018

of the spigot; if we fill the bucket, that water is going to shoot out
of the spigot. This difference in flow is analogous to voltage. Volts
are the measurement of the potential of electrical current between
two points. Voltage fluctuates, but within a given range - in the
U.S., this range is between 100 and 130 volts for standard circuits.
Now, the diameter of the spigot is going to determine the
rate of flow of that water. A very small spigot is only going to let out
so much water, whereas a large spigot will let it rip. The spigot's size,
or capacity, is analogous to amperage. Amps - the number of electrons actually flowing past a given point in a given period of time -
are what you really have to pay attention to.
Finally, if we measure how many gallons of water we actually
get flowing out of this big bucket, that would be wattage: the actual
work being done. For all intents and purposes for any given component, wattage is a constant.
Flowing electrons have the side effect of producing heat. Too
much heat, of course, creates fire. Aside from electrocution, fire is
the biggest danger from electricity. To help prevent electrical fires,
every component has an ampacity rating - the highest number of
amps that the component can handle safely. In most situations, with
the kinds of equipment we deal with, the rating will be between 15
and 20 amps.
When you arrive at a location, it's a good idea to first check
out the breaker box. Right on each breaker will be a printed ampacity; generally you'll find 15- or 20-amp breakers in most residential
and commercial locations. However, that rarely means you'll actually
have the full 15 or 20 amps at your disposal. In a perfect world,
you'll have an amperage meter that you can clamp on to your hot
lines for each breaker, allowing you to see what is already being

American Cinematographer

Andrew Lesnie, ASC, ACS photo by Barry Wetcher, SMPSP, courtesy of Warner Bros. WagBag images courtesy of William Wages, ASC and the AC archives.
All other images courtesy of Jay Holben.

SHOT CRAFT

Table of Contents for the Digital Edition of American Cinematographer - March 2018