Power Question - Long cables

[Pattyjae]

Hi everyone, I'm new to the forum and didn't really know where I should post this, but this seemed like the best place. I am a film student a few weeks out from working on my final year film and have a few concerns about setting up lighting in a particular location.

The location is in rural Australia in an old shed on a farm. The closest power source is approximately 100 metres (328 feet) from the shed and I need to power a number of high wattage lights simultaneously. As far as I am aware, the power source (house) has two circuits, each with 5000W. Below is a picture of the power box, each circuit has 250V and 20A.

My question is this: is it possible to run a heavy duty extension cable (Or multiple cables) to the shed and still have useable power? Or is it just too far away to be realistic/safe? Are there any alternatives?

Our last resort is to hire a generator but as we will be shooting for close to a week this will add a significant cost to a very stretched budget and also provide noise issues. We will need at least 3000W usable power to create the lighting set-up desired.

Thanks so much!

Patrick Jaeger

 

[Knobhead]

Lets assume your using 3 X 1000W lamps. Run 3 heavy-duty extension cables from the house, preferably split between the two power circuits.
You will have to have the cables made up for you, I don’t think you’ll get them off the shelf.
I tried running 3KJ of flash lighting for stills off a generator, the generator just stopped when the units called for a charge!

 

[Pattyjae]

Thanks Tony, would the situation be any different if I was to run a 2000W lamp off one of the cables? What do you think the limit would be per cable? Also do you think it would it be possible to run a number of smaller lights from an external RCD unit at the 'shed end' of one of the cables?

 

[Knobhead]

Without seeing the situation it’s hard to say. You need to talk to someone local.
With long cables you will experience volt drop this will change the colour temperature of the light source. The bigger the cables the better, it will minimise this problem.
With computer editing I don’t suppose this matters now.

 

[Pattyjae]

Thanks! So with the voltage drop I assume the maximum wattage output is also affected due to W=VA? Will I also lose amperage? What spectrum does the colour temperature change to? I assume it would lower the colour temperature thus creating a more red/orange coloured light?

Thanks

 

[Caerdydd]

Hello,

As your volts drop you will start to loose colour temperature, if your using a discharge lamp, HMO, msr etc they will simply not strike if the volts are too low.

You need to run multiple cables in 2.5mm Ho7RF rubberised cable, ideally jumping from 13a to 16A at the socket running the 100m in 16A then jumping back down. Beware of plugging them both into a double socket, as that's not a great idea. Always a good idea to have plug in rcd's as you don't have a tv spark with you.

Are you filming day or night scenes?

Can you not just use some kino flo to keep the power right down?
Caerdydd. (TV & Film Spark)

 

[Pattyjae]

I will be using mostly incandescent lights, we are filming both day and night scenes in the same location. I am using a few kinos but cannot light the whole scene with them, they won't provide enough light and are too soft to be the keylight to create the desired look.


"You need to run multiple cables in 2.5mm Ho7RF rubberised cable, ideally jumping from 13a to 16A at the socket running the 100m in 16A then jumping back down. Beware of plugging them both into a double socket, as that's not a great idea."

I don't fully understand this paragraph, are you able to simplify it? My technical knowledge doesn't stretch this far I'm afraid

In terms of the plug in RCDs, I was planning to have them plugged in straight from the wall sockets, then the extension cables and then another RCD/powerboard so as to run multiple lights from the one long cable stretch.

 

[Caerdydd]

Sorry forgot your in Oz.

HO7RF Cable, is a type of cable with a rubber sleeve outside, instead of normal cheap pvc. So it's a lot more tough, and is the standard for use in TV/Film, and outdoors.

Make sure the cable you use has a CSA of 2.5mm2, and don't just plug lots of 13A extension drums together, as normally they are only 1.5mm2

You'd be better off running 2 or 3 cables and putting 1kW on each, as the lower the current the less the voltage drop will be.

The usual warning, and why we exist....... Employ a TV spark for the day, it will cost less than a gennie and no one will get hurt....

If you find the voltage drop is causing the colour temp to go below 3200k, and your balanced for tungsten then try adding an eighth CTB. (Lee filters 218) increase temp by 200K.

 

[Pattyjae]

So a CSA of 2.5mm2 is minimum? Would I get better results using larger cables? Some people have suggested 4.0mm2 or 6.0mm2.

In all seriousness, I don't think we can afford a TV spark. A decent silenced 6.5k generator is $300 a day which is too expensive, and I assume a spark would be higher than this?

For the night scenes I plan to drop on 1/2 or full CTBs to most lights and balance to tungsten. So the voltage drop would not be noticed too much if it was minimal. And I could always balance lower to say 3000k? How rapidly does the colour temperature drop with voltage loss?

Is another option to get an electrician to set up a temporary feed from the house to the shooting location before shooting?

 

[Knobhead]

If you for a 4 or 6mm cable you will have the problem of connecting in to socket outlets, it simply wont fit a plug. 2.5 will be a bit of a push. Get a local spark to make some leads up for you, you can then tell him exactly what your wanting to do. He can give better advice than we can being 1000’s of miles away.