Stage Electrics – Lighting Distro for Dummies

Wednesday, May 6th, 2009 - Learn Stage Lighting - by:

A brief guide to the understanding and using of electricity systems in stage lighting, we start by looking at the basics of how electricity arrives at the stage and common equipment used in stage electrics.

Reader curiosity about power equipment and it’s uses has sparked (?!) this article. We won’t go through all the ins and outs of electrical theory but instead give you an overview of the systems involved and how to recognise certain elements.

Stage Lighting Rack

Disclaimer: This article is intended to provide some insight into the working of a professional stage electrical system for the beginner. It does not provide comprehensive training in electrics or safety and should not be viewed as such. The design of a stage lighting electrical system should be entrusted to an experienced and competent person. No warranty is implied concerning the accuracy of any information contained therein. On Stage Lighting can accept no responsibility for any inaccuracy of information or for any loss, damage or injury arising from any interpretation of its contents.

Stage Electrics and the Lighting Department

Historically, the wrangling of show electricity has been entrusted to the aptly named Electrics Dept. in theatres or the Lampies in a concert touring environment. These days, sound crew and riggers have an increased knowledge of power distro and often take care of much of their supply management and while on larger shows, a whole separate Mains department is common. No wonder, electricity is the one thing that we really can’t get by without.

While many departments use power, the overall design and distribution of a safe and bombproof electrical supply still often falls into the hands of the LX crew. Temporary power distribution equipment for events is commonly of the “plug and play” variety which doesn’t require a degree in electrical engineering to connect a system together but it does a good understanding of electrical theory and safety.

Anatomy of Stage Electricity Supply

It’s important to understand a little about how power arrives for us to use on stage, without going into all the details about substations, transformers and power stations.

Incoming Supply – With any luck, the venue has one or more incoming electrical supplies (usually 3 Phase) that comes in on a hefty set of cables. Big Cable = Big Power. The incomer(s) ends up in some kind of box ready to be split off to different parts of the building. You shouldn’t ever need to see the incomer but just know that it’s there.

Distribution Boards – Supplies from the main incomer are sent to a number of dist boards situated around a building depending on the electrical needs of each area. Each board has a set of switches that do different things and recognising them is important, particularly if you have a supply outage “upstream” from your kit. We’ll go into that in detail further on.

It’s also good to understand that some distribution boards, particularly smaller ones, can be fed from another distro panel – worth knowing in the case of a supply interruption.

3 Phase and Single Phase

When you’re new to stage lighting, 3 phase electricity is perceived as both mystical and dangerous – something scary and hugely difficult to comprehend. Let’s just clear this up – ALL ELECTRICITY CAN BE DANGEROUS. It can kill you, 3 phase or single phase.

Is 3 phase electricity more dangerous?

In the UK, our supply voltage is around 230 volts. This is the Potential Difference between the supply and Ground and if you get a Single Phase 230V electric shock it can at least ruin your day if it doesn’t kill you. With a 3 phase supply, each phase to Ground still has a p.d of 230V – however, the p.d between two phases can reach up to 415 Volts. So, what we call a “phase to phase” shock is more likely to kill you. In that sense, 3 phase is more dangerous but the thing that really does for you is the current (Amps). All large electricity supplies deliver lots of current, that’s their job. A domestic 13A socket will send you 13 Amps of sizzle before it fuses (plenty to knock you off your perch). Large lighting supplies can deliver >400 Amps and three lots of it too!!!

Let’s let the Grim Reaper take five for a moment and try to get behind the mystics of 3 phase electrics. Because of the way electricity is generated, it comes to us in three different supplies. What do I mean by supplies? Well, take a the socket on one side of your kitchen then another on the opposite side. Chances are, they are both different outlets of the same supply – and on the same phase. In fact, unless you live is a big house, you are likely to only have one phase coming into your house in total. One supply. Your neighbours house may well be on a different phase to you, with neighbours on the other side on the third phase. They are on different supplies.

We use all three phases in stage lighting systems because it brings more power into one place. The use of a large 3 phase cable is where confusion sets in but it’s just three supplies – 3 x Line/Live conductors and 1 x Neutral (shared between the supplies) plus an Earth. 3 Phase plugs usually have 5 pins, one for each conductor (actually, some 3 phase plugs have only 4 pins but we don’t need to worry about that right now).

Stage Electrics and Protection

Festival Lighting Rig

A major part of safe electrical systems design is what we call protection, things that stop people getting hurt by electricity and the fallout when something goes wrong.

People protection – The parts of an electrical system that protect people from electric shocks cut the supply at the first sign of trouble. In the UK, Residual Current Devices (RCDs,) are built into different parts of the distro system particularly at the “user” end such as on stage supplies to backline equipment. An ideal show supply would have individual RCDs protecting small power socket outlets, moving lights, consoles etc meaning that any interruption does not remove the entire supply. RCD’s are called GFIs in the US.

Kit protection
– Fuses or MCBs (Miniature Circuit Breakers) provide overload protecton – cutting the supply if any equipment draws more power than the supply was designer for. Overload on a circuit is a good way of detecting some kind of fault and ditching the supply prevents fires and excess damage to kit. Fuses or MCBs don’t save people.

Recognising Switches

On venue dist panels and lighting distro kit, switches are very much the thing. Working out what they do is the first step on the road to recovery in a power outage. If you do suffer from a loss of power, work out where in the stream the loss has occurred and switch off all outlets downstream of it before firing it up again. The most important part about re-energising (fancy word) is to do it in a controlled manner and with a full understanding of the entire system. Flicking a breaker back on when your buddy has his hand in the back of another distro will make you either unpopular or a criminal or both.

Isolators
– A switch that simply isolates the power. Maybe a big, single red switch on a dist board or a separate box with a toilet flush handle, the isolator is used to shut off power to a panel when performing maintenance on the installed system. The isolator is not like an MCB or RCD, it doesn’t go off of it’s own freewill.

It is worth knowing that some electrical installation boxes have some form of isolator that activates when the front panel is disturbed or door is opened, particularly ones that have live terminals inside. If you are still reading this article, obviously you wouldn’t be poking around in such a box but mysterious power outages have been solved by banging on a worn isolator door to shut it properly.

RCD’s – RCD’s on a panel or distro box are often different to the majority of other switches in appearance. They usually have writing on them that give details of the tripping current such as 30mA or 0.003A and have a Test (T) button. If a RCD can’t be reset, it’s likely that you will need to unplug all equipment downstream before fault finding.

MCB’s – MCB’s usually make up the majority of switches on a board and provide an isolator to the circuit as well as overload protection. Usually marked up with their type letter and their maximum power rating in Amps such as C16 – a C type rated at 16 Amps. 3 Phase MCB’s look like a line of 3 switches with their handles joined together and are again marked with their type and rating.

Temporary Stage Power System Basics

When designing a stage power system, you essentially have the same elements as the building supply we talked about at the start:

Incoming Supply – From the venue, a facility panel with one or more sockets. These sockets might have their own isolator switches, RCD’s or overload protection near them but they could also be upstream and the dist board supplying the outlet. It’s good to find out where this is before you need it.

Main Distro Box – Often receives a large 3 phase supply and splits it down into smaller outlets either 3 or 1 Phase. Each outlet has it’s own MCB protection and the whole box may have some form of RCD. The RCD on a Main Distro box might have a key switch to disable it – this is for situations where you have adequate RCD protection downstream of the box and wish to eliminate the chance of a whole supply outage. The switch isn’t to be used just coz you have earth problems with the kit and the supply keeps popping out.

Sub Distros – Further down stream, you might have small supplies feeding other distribution boxes for a load of moving light supplies, dimmer feeds and power for other departments such as sound or rigging. What each department requires is very much where the system design starts (with regard to how much total power is available at the incomer too, of course).

Individual Feeds
– Dimmer outlets, cables to moving lights, sockets for the band etc. This is where the user meets the juice.

The End Result

A stage electrics system is just like any other power distribution. It starts with a very large supply and cascades it down through various types of protection until it arrives where it is needed via a much smaller socket.

Using specifically designed distro kit with competence, creating a safe and reliable power system doesn’t have to be hard. Getting a rock solid incomer in certain parts of the world can be tough and getting a decent earth in the desert even harder – but that’s another story.

Electricity should be taken seriously. Stay safe.

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Rob is a Lighting Designer and Moving Light Programmer and currently Senior Lecturer in Technical Theatre Production at Bath Spa University in the UK. He is also the Editor of On Stage Lighting and runs workshops in stage lighting practice.

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