Staying safe on stage is more than a matter of simply making sure that willing hands are available before taking a dive. Knowing how to properly handle the mains power we all need is also crucial to performance health...
Whatever the size, complexity or cost of your live sound rig, one of the first — if not the first — question on your mind when you get to a venue will usually be "where do I plug it in?" Depending on the venue, the answer can vary from a wall-socket behind a plant pot to a dedicated and professionally-installed supply that is reserved for your exclusive use, fully tested and certificated, and for which (with any luck) you'll have brought an appropriate connector. Whatever you encounter, you'll need to know some basic rules. When it comes to portable live-sound systems, this means firstly, using a suitable electrical supply; secondly, using suitable equipment; and, thirdly, connecting and using that equipment safely.
A good first step, then, is working out what current your equipment will draw from the mains. The power rating of each piece of gear should be stated on a panel fixed close to the mains connector, or where a fixed mains lead enters the equipment. The power rating may be expressed as a current (in Amps) or as a power figure in Watts. It's generally best to work out the total current your gear will draw, adding up all the individual figures to find the total load you'll be connecting to the mains. To convert Watts to Amps, divide the Wattage figure by 230 (mains voltage). As an example, a piece of equipment with a mains power rating of 100 Watts (not 100W of audio power) will draw a little under half an Amp. In a small venue that is only offering 13-Amp sockets of the normal domestic type, you can then work out how you need to wire up. If the total connected load of your system — including the backline equipment — is comfortably within the rating of a single or double 13-Amp socket, it's perfectly alright to connect it all from a single point. After all, that's what they're designed for! Try to avoid too many connections between this point and your equipment. It's much better to have a single power lead of the required length than two shorter ones joined together: less to go wrong!
The table below gives a rough guide to the supply current likely to be required by a band with three backline amps and a vocal PA (based on UK voltage). Bear in mind that equipment may demand a much bigger supply current when it is first switched on, so don't be tempted to turn everything on from a single switched socket — you wouldn't want to do this anyway, for many other reasons, such as risking a huge pop through your speakers! Also consider that the power that you can safely run your system on may not be enough to realise its full performance capability. Any system capable of delivering good bass power will need to draw a hefty current from the mains, and if, in the above example, we were to replace our typical small speakers with, say, a pair of Mackie SA1521s, the makers recommend that each speaker's mains supply is capable of providing seven Amps at 230 Volts! This is, of course, not a constant current requirement, but it does illustrate how important a good power source is for getting the best from your gear.
|Equipment||Mains Power needed||Mains Current needed||Amps|
|2 x 240W active PA speakers||480W x 1.4 = 672W||672 / 230 = 2.92 Amps||2.92|
|Mixer||100W (stated)||100 / 230 = 0.44 Amps||0.44|
|2 x rack processors||20W each (stated) = 40W||40 / 230 = 0.17 Amps||0.17|
|3 x 100W backline amps||300W audio x 1.4 = 420W||420 / 230 = 1.83 Amps||1.83|
|ROUNDED UP =||5.5 Amps|
If the venue in question is unfamiliar to you and you are responsible for providing and operating the PA, always check that the supply you're asked to use is suitable. Just because it's a 13-Amp socket doesn't mean that it's capable of supplying 13 Amps: it may have been DIY-installed as a spur from a domestic ring main, originally to light a garden shed or run a fountain or something! If you're operating in any kind of business or commercial premises, they should have an up-to-date electrical safety certificate. A quick look at the distribution board or consumer unit should show the overall current rating of the circuit you'll be using, and you can also see if it uses old-style wired fuses or the more modern MCBs (Miniature Circuit Breakers), which react more quickly if the rated current is exceeded.
Fuses and MCBs do not protect you from electric shock, so always make sure that your system is fed via a residual current device (RCD). This could be at the main board/box, on the socket itself, or at the point where a separate spur is fed. If you're not sure that this is the case, use your own RCD, either as a plug type or one of the RCD plug-in adaptors readily available for a few quid from any electrical retailer. The RCD should be as far 'upstream' as possible so that it protects as much as possible, and wherever it is, make sure you test it before use, by using the built-in test button. If it doesn't seem to work, find another!
A final word on RCDs: they are there as a backup in case anything goes wrong, not as a substitute for poorly-maintained, faulty or unsuitable equipment.
Having found a suitable supply point, you now have to feed it to all your equipment. For all gigs where a 'proper' supply is available, I use a professionally made portable distribution box, which has a single 32-Amp inlet and 32-Amp breaker, feeding four 16-Amp outlets, all via separate combined RCD/MCBs. Although, on the face of it, I've got four 16-Amp outlets, giving a total of 64 amps, I can only use 32 Amps overall, with each outlet limited to 16 Amps. I run my front-of-house speakers from two of these feeds, the monitors and desk from the third, and the stage backline from the fourth. This splits up the load and ensures that each feed is fully RCD protected. As mentioned earlier, it is always best to have an RCD as far upstream as possible, and I would ensure that my original 32-Amp source incorporated suitable protection if available.
For smaller indoor events, a single 13-Amp fused RCD plug feeding into a multi-way distribution board (four or six sockets) is fine, as the total current can't exceed the 13-Amp fuse rating in your RCD plug. From this distribution board you should try, where possible, to connect direct to equipment, or feed the equipment in logical groups. Normally, you can take the initial feed from a socket at the back of the stage and run all your backline straight from this, with one feed going off to the PA system. If you need to use more than one socket in a small venue, ensure that all your signal connections are balanced, and never, ever remove an earth connection to get rid of hum or noise. Also take care when using those 'flying saucer' extension reels. They are very useful and neat, but remember that their maximum current-carrying rating only applies when the cable is fully unwound.
All electrical equipment, including cables and connectors should be stored and used in dry conditions unless it is designed for outdoor wet weather use and carries an appropriate IP rating (for mains connectors this will usually mean industrial 'Ceeform' types — coloured blue — either rated IP44 (which is splashproof) or IP67 (which is waterproof).
In this article I've taken a very basic and superficial look at the power side of live sound. There's a lot of additional good advice to be found, and it's well worth taking a professional approach and discovering as much as you can. After all, if you were going to jump out of an aeroplane you would, presumably, want to know that your parachute was (a) of the correct type; (b) correctly installed on your person; and (c) recently tested! Electrical power is a serious business, so if in doubt, ask a qualified electrician. If you don't know one personally, someone you know will, or you can look one up in the phone book.
There are also plenty of useful pages on the Internet. The UK's Health and Safety Executive web site, for example, has a lot of relevant information and links to some very good guidance publications. Check out www.hse.gov.uk.
- Damage to cables or plugs, including cuts, cracks, abrasions, bent or missing pins.
- Previous repairs or modifications, including exposed or taped-up cable joins and unsuitable connectors.
- Exposed inner conductors where the cable enters the mains plug.
- Signs of damage to casing and covers.
- Obvious signs of previous problems; for example, signs of water, moisture or heat damage.
- All wires are firmly attached (screws nice and tight) to the correct terminals, with no bare wires showing.
- The cable outer sheath is firmly gripped by the cord grip.
- There is no debris or signs of damage internally.
- Additional testing of earth integrity and insulation.
- Test results recorded and appropriate labels attached to the equipment.
- Failed equipment identified for disposal or repair.