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Appearing like trenches dragged into the earth, sunken lanes, also called hollow-ways or holloways, are centuries-old thoroughfares worn down by the traffic of time. They’re one of the few examples of human-made infrastructure still serving its original purpose, although many who walk through holloways don’t realize they’re retracing ancient steps.

The trunk line for a stage. But why so many cables for one generator?

An extension cord (a.k.a. a stinger in film speak) is made out of three cables: the ground, the neutral and a hot leg. the hot leg with the neutral produces a 120 volts. 

120 Volts outlet

And pretty much every plug in your house is a 120 Volts. And most lights we use in film are 120 Volts: a hot leg, a neutral and a ground. Easy breezy.

Some homes will have 240 Volts outlets which is two hot legs and the ground. 

240 Volts household plugs - note that they have 2 hot legs. 

If you look outside your home, chances are that the power going to your home from the electrical pole will have a metal cable with two black shielded cables coiled around it. The metal cable is actually the neutral and the black shielded cables are two hot legs - the ground is provided by a pole into the ground at your breaker box. Most homes, have 240 Volts available to them. Having a ground, neutral and two hot legs is called single phase.

In film, when using a generator or stage power, you will normally use a 5 piece cable run with three hot cables - this is called three phase.

5 wire ‘banded’ with Cam Lock connectors. Green is ground, White is neutral and the Red, Blue and Black connectors are the hot legs. 

A standard “three phase” run is 5 pieces of cable: the ground (green), the neutral (white), and three hot legs (red, blue, black). Each hot leg with the neutral creates 120Volts and two hot legs together creates 208Volts (not 240 Volts - don’t ask). You never use all three hot legs together FYI. So a three phase cable run gives you a lot of options.

5 wire banded going into a distro box. 100 Amp bates to a lunch pale to a stinger. 

Sometimes you need to run more power than the cable allows or when running a long run you might have issues with line loss (voltage drops over distance). 

4/0 AWG cable! This is heavy back breaking cable. Note that each piece is individual and not ‘banded’ together like the 5 piece ‘banded’ cable shown earlier.

4/0 AWG wire is the thickest (i.e. most copper) cable we have and allows for about 400 Amps at 120Volts (this is how we roughly calculate power in the film world). So if you have three 4/0 AWG hot legs, you could run up to 1200 Amps. Well, sometimes that is not enough as the generator might very well provide more than 1200 Amps of power. And to account for line loss if there is a long run, we often double up the cable. So for a single three phase run you might very well run 9 pieces of cable: 1 ground (you do not need to double this up), 2 neutral, 2 of each of the three hot legs. So a single run of power on a “big show” can get quite large.

The initial run of cable form the source to the set is called the trunk line. Once you get to set, the trunk line normally goes into a “spider box” which splits the run into your more conventional 5 piece cable runs.

A Spider Box. Trunk line comes into the Spider box and splits it into different runs. 

Other solutions to run large amount of power over a long distance with minimal cable is to run a higher voltage run and use step down transformers. This is dangerous stuff and if you don’t know what you are doing, can kill you. When you find yourself at that level, you will be hiring an outside firm or a professionally licensed electrician to help you.

Bell Labs, 1970