As a Miami gaffer, I thought it might be helpful to teach the basics about electricity as it applies to producers! Filmmakers often need to be a jack-of-all-trades (doesn’t mean they’re the master of none).
Although you’ll have a dedicated electrician to run power to your set, you still need to have the basic knowledge of power distribution, electrical safety and power sources. This helps you coordinate with your Miami gaffer and best boy more effectively to avoid any electrical faux pas on a your film set. So here’s the electricity 101 for film and television productions.
Power Distribution on Movie Sets
In order to understand power distribution, you should have a clear understanding of voltage, wattage and amperage, and how they relate to each other.
One simple way to understand that is by using the water analogy. Water pipes are analogous to electric circuits. Electricity flows through circuits, just as water flows through pipes. Of course, water and electricity have different characteristics, and so the analogy is not 100% accurate, but it helps you understand the relationship between voltage, wattage, amperage and resistance.
Voltage is basically the difference in energy between two points in an electrical field. If you compare electricity to water, then voltage is comparable to water pressure in a water pipe. The more the voltage, the faster the electric charge flows through a circuit. However, high water pressure doesn’t always mean that a lot of water is flowing through of the pipe. Similarly, high voltage doesn’t necessarily mean high volume of electricity. That brings us to amperage.
Amperage is analogous to the volume of water flowing through a pipe per second. It is basically the measure of how much electrical charge is flowing past a given point in one second. Not to get too scientific but the symbol of voltage is ‘V’, while the symbol of amperage is ‘I’ or ‘A’.
Now if you multiply voltage with amperage, you get power or wattage.
P (wattage) =V (voltage) x I (amperage)
Or I (amperage) = P (wattage)/V (voltage)
Use this formula to calculate how many devices, hair driers, computers, lights printers your Miami gaffer can plug in to a power strip or outlet on the wall or coming out of a portable generator, before you flip the breaker.
How to Avoid Overloading a Power Strip
Typically, a circuit breaker can handle a maximum 20 Amps of current. And in the U.S., we mostly have 120V circuits. Now if you use the above equation (P = V x I), a typical circuit breaker can withstand maximum 120 x 20 = 2400 watts of power.
That means, you can plug in one 2K (2000 Watts) light or two 1Ks to a 20 Amp circuit. If you plug in one 2K light and one 1K light, the circuit breaker will flip or break.
But for safety reasons, most electricians and gaffers in Miami would recommend using maximum 80% of the breaker rating. So if you plug in one 2K light to a 20 Amp power strip plugged into a wall outlet or portable generator, then you must avoid adding more load or devices to the same circuit.
In order to calculate how much you can safely plug in to a single wall outlet, electricians often use paper Amps.
What is Paper Amps?
Paper Amps is a way of calculating roughly how much you can plug in, before you overload the circuit breaker. The way it works is simple. Take all the wattage of all the lights you’re plugging in to one circuit; add them all together; and then divide them by 100.
Did you notice that we are dividing the total wattage with 100, instead of the typical 120? That’s because we want to keep a little buffer or safety net for poor calculations!
To understand the concept of paper Amps and how it applies in the practical world, let’s take a look at an example. Let’s say you want to plug in one 1K (1000W) and two 650W Fresnel lights to a 20 Amp circuit. Is it possible? Let’s do the math.
(1000W + 650W + 650W)/100 = 2300/100 = 23
So no, you cannot safely connect those three lights to the same circuit because you’ll trip the breaker.
Selecting the Right Extension Cord
On each extension cord, you’ll see ratings in Amps. Let’s say the rating for an extension cord is 15 Amps; and you have 120V circuits, which is everywhere! So if you use the P = V x I formula, the cord is capable of carrying 1800 watts load. But for safety, you should use maximum 80% of the wattage your cord is capable of carrying. In the above example, although the cord is capable of carrying 1800 watts, you need to make sure it is not carrying more than 1440 watts. These extension cords can get hot and melt!
Apart from Ampere ratings, also consider the length and thickness of an extension cord. It is always safe to use thicker cords when you’re running power from multiple sources to a single location. The thickness of a cord is measured in gauge. The lower the gauge rating, the thicker the cord.
Ideally, your gaffer should use a 12 gauge cord for running up to 2000 Watts of power to your set. If you’re running power from a long distance source, consider using one long extension cord, instead of multiple shorter cords. But one problem with longer extension cords is that they often cause a voltage drop due to wire resistance. You can minimize the voltage drop problem by using thick-gauge extension cords.
Types of Portable Generators
Portable generators [aka geni] come in a wide variety of shapes and sizes, with different features to suit different needs. So the first thing to do is define your needs. Is your Miami gaffer planning to use a geni to power sensitive electronic devices, such as, laptops, printers, music systems and fax machines? If yes, then look for a generator capable of reducing voltage fluctuation due to harmonic distortion. A Honda generator is perfect for that! You’ll usually need clean, reliable power on movie sets. To that end, choose the right type of generator for your film production.
There are mainly three types of portable generators available in the market. They are;
- Brushless generators – This type of geni typically has up to 23% voltage waveform distortion – not suitable for sensitive electronics and HMI and Kino Flo ballasts in a film production. Normally you will only find these in 3rd world countries or in the Caribbean.
- AVR generators – This type comes with voltage waveform distortion of up to 19.5%. Although they interact well with HMI and Kino Flo ballasts, they are not a safe option for your sophisticated electronic equipment.
- Invertor generators – With voltage waveform distortion of less than 2.5%, these generators are perfect for use on film shoots. You can safely use them to power both your HMIs and sensitive electronic devices. Also, they are lightweight and not very loud. Most of them come with an eco-mode to offer you more fuel efficiency. For instance, if you switch to the eco-mode of Honda 2000 Watt Generator, it can run up to 15 hours on a single tank of gas.
Some other important considerations when choosing a generator for your film or television productions include your total wattage requirements, whether it has both an electric and a pull start option, and whether it comes with wheels.
So there you go, with this info in hand, your Miami gaffer will be proud!