It's invisible, it's powerful and it kills if you mess it about. Ben Duncan considers electricity and the ways to keep it friendly.

ROCK 'N' ROLL and electricity are dangerous bedfellows. The former produces sweat and often involves lots of orange juice/water/beer. There's also lots of hassle and panic, so suspected faults involving the mains juice (not to be confused with orange juice) don't always get checked out. Gear gets battered, earth wires come adrift. And despite what you might think, fuses don't prevent electrocution, and earth connections offer limited protection. So what can be done to aid survival? First, let's examine the sparks.

"A conductor is something which has the property of transmitting electricity; an insulator is the opposite, a non-conductor of electricity."

Your body is covered with an insulator (skin), but the fluids inside are all excellent electrical conductors. And all your motor mechanisms, from the involuntary (heartbeat, respiration) to the musical (drum thrashing, guitar strumming), depend to a lesser or greater extent on tiny, varying electrical potentials in your nervous system.

Electrocution is simply the wholesale interruption of the body's nervous 'electricals' by a much more powerful current. This blocks your reflex actions, there may be paralysis so you can't let go of the live object, and worse the heart's own vital rhythm is disrupted.

Above a certain current level, and in certain conditions, the heart stops altogether and only prompt and skilled medical attention can bring back life. Even then there may be brain damage, paralysed limbs or scarring for life (no HM jokes, please).

And remember, if the very worst happens and someone from your band falls electrocuted to the floor DON'T dive in thoughtlessly and grab him. He could still be live and draw you into the deadly circuit. Turn everything off and if possible try and pull him clear with a coat, dry towel or at least something better insulated than your own skin.

VOLTAGE OR CURRENT

To understand mains electricity, think of a water pipe. Voltage would be the pressure of water in the pipe, and current would be the amount of water (its volume) actually passing through. Yes?

Continuing this idea a little longer, to get a large volume of the stuff into your body there'd need to be a fair pressure behind it. With minimal pressure (voltage) it'd have a job getting through unless the resistance offered by your body is very low (a 9 volt battery across a wet tongue can still give you a jolt).

But the severity and danger of an electric shock are not only related to how much current flows (see the table nearby), but where it travels. (For a start, if the shock travels down the left hand side of your body rather than the right, that's going through your heart — an even greater risk. Experienced roadies can often be found shoving their left hands in to their back pockets whenever they get suspicious about mains. There's less chance of them unthinkingly reaching out with it and completing 'the-circuit-of-greatest-danger'.)

How much voltage is needed to get these sorts of currents to flow depends on the resistance the human body will offer it — and that can vary dramatically.

Bare flesh — a wound, say — gives the voltage direct access to the body's internals, which have a low resistance. So if live power is applied to a grazed hand, and you're earthed via a wounded foot, a surprisingly low voltage has the potential to kill — say as little as 60 volts.

On the other hand (groan), the thick calloused skin that musicians and other craftspeople develop on their fingertips greatly amplifies the circuit's (ie your own) resistance. Therefore a much higher voltage is necessary before the same lethal current level is passed. Moral? "Cast not thy hand into The Ointment, and love ye Callouses." Dry skin is also good news — for the same reason.

Anything over 70 volts DC or 50 volts AC is officially regarded as dangerous to life. The 110-volt mains in the US causes relatively fewer fatalities, but death is certainly possible and you may be one of the unlucky ones. So it's best to regard all mains supplies with deference.

Some high power amplifiers can also put out potentially dangerous voltages. For example, 500 watts into an eight-ohm speaker spells 63 volts AC. True, this is highly unlikely to kill, but it can still belt you so there's always the danger of being thrown backwards or falling off stage.

If in doubt, tum down power amps before playing around with the speaker leads — the full output voltage is only present when the amp's going full bore.

Shock-Avoidance Gadgets

Fuses are mainly intended to prevent fires and are relatively slow to act. For instance, with 10 amps flowing through you, a five amp fuse will blow about one second after the ten thousandth of a second (10mS) needed to stop your heart.

The only gadget that offers reliable protection against electrocution is a current-balance current-breaker (we'll call it a circuit breaker). It monitors the current flowing in the live and neutral wires, and promptly breaks the circuit if the two currents differ — working on the basis that any extra current will be going somewhere it shouldn't (possibly through you).

Although the protection itself is reliable, a circuit breaker offers NO guard if you wire yourself up between live and neutral. This is rare and highly unlikely to arise on stage. By far the most common 'bad connection' is between live and something tied to earth (a concrete floor, say, a mike, or an amp chassis), and the circuit breaker emphatically protects against this.

Circuit breakers have two current ratings. One will be given in amps and is the current level that the switching mechanism can safely handle. For most purposes this will be 13 amps, to correspond with the mains socket's rating.

The second rating is in milliamps (mA) and refers to the maximum permitted difference between the live and neutral currents before the breaker trips out. That's the maximum current that can pass through you. For us frail humans this must be below 40mA. Thus the standard trip current for all normal purposes is 30mA, and you should choose a circuit breaker with this rating.

For the home set-up, a company called MK make a circuit breaker which fits in the space previously occupied by a double 13 amp wall socket. Trouble is you lose out on one of the two socket outlets because of the space being occupied by the breaker. The plus point is speed and neatness. After you've turned off the mains power at the fusebox you can replace all the double sockets in a room with circuit breakers in a matter of minutes. The one to ask for is the 6300 Sentry socket (about £35).

Meanwhile, for stage use, B&R Electrical Products make some easy-to-use breakers, most of which are available from good high street electrical shops. Their Mainsafe H07 circuit breaker (about £20) is an enlarged 13 amp plug containing the breaker. Wire this special plug on to the end of your principal extension cable and you're protected.

Or, if you simply hate wiring up plugs, quite a few companies make one-way adaptors containing the breaker which you simply plug in to any wall socket and then plug your gear into its socket. B&R make the Powerbreaker 20; Smiths Industries the CB001; and MK the 6230. They're all rated at 30mA and priced at around £20. Trouble is they're easily nicked.

If you're short of cash, the last adaptor-type is best because it's not dedicated to specific outlets or items of gear, and one breaker alone can be carried around and placed where it's needed most. Don't forget that the breaker only senses what it's powering, so the nearer you get to the ultimate mains outlet, the more protection, you'll achieve. So try to ensure that all your gear is powered via the one breaker.

SURVIVAL TIPS

1 Never put drinks on top of or near any mains powered equipment. If the liquid spills, it'll damage the gear at least, and you'll also risk electrocution when you next turn round and grab the can or glass. Down on the floor beside the speaker cab is best.

2 If you're fiddling with anything mains powered, standing on a dry and well insulated floor marginally increases safety (wood, vinyl tiles or carpet, but not concrete). But if you use one hand for the fiddling, make it the right hand — remember that roadie story.

3 Don't disconnect the green/yellow mains earth wire from any mains plug. This is often done as a makeshift solution to stop irritating buzzes, but equally often it never gets sorted out properly. Bad buzzing means there's something wrong with the earthing (grounding) in your particular set-up — so ask the shop where you bought your gear to help you put things right (this is all part of their good service).

4 Regard the green/yellow wire in the mains plug as sacrosanct. Whenever you have a few minutes to kill (ha ha) try taking the top off a plug and checking inside. Are the screws tight? Is the green/yellow wire firmly connected?

5 Wire your mains plug perceptively. At some point someone will trip over a lead and possibly tear the cable from the plug, perhaps only partially. If the earth wire is tom out of its pin this is dangerous enough, but worse, it may come into contact with another terminal in the plug, making the equipment's supposedly 'earthed' metalwork 100% live (and you potentially 100% dead). It's always a good idea to make the green/yellow earth lead longer than the others in the plug. Give it more slack. That way when the cable is pulled heavily, the neutral and live leads will break away first.