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The Shocking Truth

electrocution for beginners


How easily can you die from electricity? Ben Duncan is not neutral on the subject.

Mains electricity is dangerous stuff, but fuses don't prevent electrocution, and earth connections offer limited protection, especially if that vital Green/Yellow earth wire has been pruned to prevent a buzz in your speakers. Now, 100 years after the introduction of mains electricity, an easy, everyday 'protect-me-from-electrocution' gadget has surfaced on the shelves of high street shops. In this gruesome episode, we tell you of the dangers of electricity, and how to go about protecting your musical career from the short, sharp shock.

How it works: Electrocution



The naked human body is covered with an insulator (skin), but the fluids inside us are all excellent electrical conductors. All motor mechanisms, from the involuntary (heartbeat, respiration) to the musical (arm beats hell out of floor tom) depend to a lesser or greater extent on tiny, varying electrical potentials in the nervous system, not altogether unlike the digital electronics in a DX7.

And electrocution is simply the wholesale interruption of the body's nervous 'electricals' by a more powerful current. This blocks out reflex actions — there's paralysis, so you can't let go of the live object, and worse, the heart's 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!)

Voltage or current?



The severity of an electric shock is related directly to how much current flows — and where it travels. As you can see from the table nearby, 1 milliamp (one thousandth of an amp) is tingling stuff à la fairground 'shocking machine', whereas 1 amp will almost certainly cause death.

How much voltage we need to get these sort of currents to flow depends on the resistance of the (human) circuit. 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 musos and other craftsmen develop on their finger tips 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". I for one wouldn't be writing this if I hadn't any. Dry skin is also good news — for the same reason.

Voltage facts



Anything over 70 volts DC or 50 volts AC is officially regarded as dangerous to life. The 110V mains in the US causes relatively few 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 8 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 the stage.

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

Left arm in de backpocket Dub



Normally, a current flowing in the body is only directly dangerous to life if it passes near the heart, lungs, and/or brain (delete where inapplicable). If it flows between your legs, or down your right-hand side (opposite side to the heart) or across your hand, you might die from concussion, by being flung backwards, but there's no direct threat.

The classic death scenario is to touch live mains with one hand, while grasping something connected to earth with the other (or vice versa). This is invariably deadly, because in passing from one hand to the other, the current must travel in the vicinity of the heart and lungs. For the same reason, current passing from the left hand and then down the left side (to the foot, thigh, etc) is equally dangerous.

Knowing this, boffins, (who often have to poke around inside gear while it's connected to the mains), will instinctively put their left-hand in their back pocket. There's still the possibility of an unpleasant shock, but the main danger — current passing near the heart — is avoided. Standing on a well insulated floor also helps — this means wood, vinyl tiles or carpet, but NOT concrete.

The catch all



If you've had a few nasty shocks, you might (ironically) be cynical about the capacity of mains electricity to be truly lethal. Trouble is, the reason why you're still around is more down to a lucky combination of circumstances than any super-human resistance. Next time, you might be sweating. Bingo, the skin resistance falls dramatically and the current flow multiplies to deathly proportions. The high current may also burn the flesh, which further increases its conductivity — so the current flow rises still further. And either way, there'll be paralysis, so you won't be able to let go if you're grasping the live object. For example, a genteel cabaret vocalist lightly touching a live mike on a stand will probably be convulsed backwards and away from the danger. But if you grasp a live mike with both hands in true R & R style, you're in real trouble. The rule is never grasp anything you suspect to be live. A quick prod with a finger will tell you all you need to know.

Practicalities



Rock 'n' Roll and electricity are dangerous bedfellows. The former produces sweat and involves lots of orange juice/water/lager/Ruddles. There's also lots of hustle and panic, so suspected faults involving the mains juice (not to be confused with orange juice) don't always get checked out. And lots of itinerancy, too, so amps get battered, and earth wires come adrift. If you're new to the stage, here are four simple rules:

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

2) Don't remove the green/yellow mains earth wire from any mains plugs. Often this is done as a 'makeshift' solution when there's a hum loop to stop an irritating buzz, but equally often, it never gets sorted out properly. So if you need to stop a buzz, use a DI or isolating box to join equipment together from the word go — or seek expert advice.

3) Regard the green/yellow wire as sacrosanct. Whenever you have a few minutes to kill (say you're waiting with your gear in a truck outside a venue whilst Joe goes to rouse the caretaker), try taking the top off a mains plug. Are the screws tight? Is the green/yellow wire firmly connected?

4) Wire your mains plugs 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 torn off this is dangerous enough, but worse, it may come into contact with the live pin, making the equipment's exposed metalwork 100% live. If your plugs are slightly... um... remiss in regard to their clamping abilities, it's a good idea to make the green/yellow wire longer than the others. The live and neutral will then disengage first.

In real life, musos tend not to have time to make all the routine checks necessary for 100% safety. And to some extent, a happy-go-lucky attitude is culled from the domestic scene: "My mum never checks her earth connections, and she ain't dead". But do washing machines and kettles suffer as much abuse as combos and PA amps?

Protective appliances



Fuses are mainly intended to prevent fires. They're relatively slow to act. For instance, with 10 Amps flowing through you, a 5 Amp fuse will blow about a second after the ten thousandth of a second (10mS) needed to stop your heart.

The only gadget which offers reliable protection against electrocution is a current-balance circuit-breaker. It monitors the current flowing in the live and neutral wires, and promptly breaks the circuit if the two currents differ.

Why? Well, if 1 Amp is flowing in the live wire, but only 1/2 Amp in the neutral (the blue one), ½ Amp is clearly going somewhere it shouldn't, and possibly through YOU.

Although the protection itself is reliable, I must emphasise the one limitation of this type of circuit breaker. It offers NO protection 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, a mike or an amp chassis), and the current-balance breaker emphatically protects against this. One other point: 'current-balance circuit-breaker' is a bit of a mouthful, so hereon, we'll simply call it a power breaker.

Power breakers have two current ratings. One will be given in Amps. This is the current level the switching pechanism can safely handle when it trips out. For most purposes, this will be 13 Amps, to correspond with the mains socket's rating. But for permanent installations, where a power breaker is wired in line with, say, a studio's entire mains supply, a 30 or 60 Amp rating may be needed.

The second rating is in milliamps (mA) and refers to the maximum difference between the live and neutral currents before the breaker trips out. That's the maximum current that can pass through you. Some power breakers have 100 or 300mA ratings. These aren't intended to save lives. No, for us frail humans the current must be limited to a much lower level, ideally below 40mA. Thus the standard trip current for all normal purposes is 30mA. Even more sensitive safety breakers are available, rated at 10mA, but these are aimed at hospitals or young children, and won't offer any useful extra protection for musical purposes. In any event, an over-sensitive power breaker can be something of a liability, as it's more likely to trip out in response to small leakages to earth. Small leakages shouldn't happen, of course, but it's still annoying to have your mains shutting off randomly and unnecessarily, and this sort of behaviour turns people off to the concept. To sum up, then, stick to the standard 30mA trip current* (* adults only).

Which format?



For the home studio, or workshop, MK (They of light switch and 13 Amp socket fame) make a power breaker cum outlet which fits in the space previously occupied by a double 13A socket.

Trouble is you loose 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 power-breakers in a matter of minutes. The one to ask for is a 6300 Sentry socket.

Meanwhile, for stage use, B & R electrical products have come up with a range of user-friendly products. The first two are available from any good high street electrical shop. Their Main safe power breaker is an enlarged 13 Amp plug containing the breaker. Wire this special plug onto the end of your main extension cable and you're protected.

Or, if you simply hate wiring up plugs, their Power Breaker 20 has the answer. It's a one way adaptor containing the breaker. You simply plug it into any wall socket, then plug your gear into the socket at the back. Trouble with this one is having it filched. Both, incidentally, trip out at 30mA, and can handle 13 Amps.

The third product is the Mainsafe H04. This is strictly an industrial product, and the 30mA, 240v version you need has a horrendous code — it's actually an 'H04-B01302-030M', and you'll probably need to order it. With this one, the breaker comes in a tough plastic enclosure, with a short cable leading to the mains plug. The advantage is that it's more... er... roadie proof.

Hints & tips



If you're short of cash, the H04 and Power Breaker 20 are best, because they're not dedicated to specific outlets, or items of gear, and one breaker alone can be carried around and placed where it's needed most. Also, 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.

Try to ensure that all your gear is powered via the one breaker.

If the breaker keeps tripping out for no apparent reason, it's trying to warn you that there's a potentially lethal fault at large. Perhaps an amp you left out in the rain when loading up last week hasn't dried out properly, and live mains is leaking to earth? Or there's a frayed mains lead, or some other fault. DON'T bypass the breaker in these circumstances. Instead, unplug anything you suspect (or unplug everything in turn) until the tripping-out stops. Once you've tracked down the guilty amp (or whatever) that's causing the trip-out, put it to one side; it's unsafe, and should be checked out by an expert. End of lecture!

The effects of electric current on the human body

Current level Effect Duration
1mA Tingling. Safe for an indefinite period
5mA Maximum harmless current level Safe for an indefinite period
10 to 30mA Unpleasant shock, but no sustained muscular contraction or damage to health Safe up to 1 second
50mA Pain, exhaustion, possible fainting, and physical injury Dangerous over 1/30th Second (300mS)
100 to 300mA Ventricular fibrillation is possible (ie: Heart beat is interrupted), but respiratory centre not affected Potentially lethal in excess of 1/10 second (100mS)
1 to 6 Amps Sustained myocardial contraction (ie Heart stops) and respiratory paralysis (Lungs stop). This level of current can also result in internal burns Potentially lethal in excess of 1/1000th second (1 mS)


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Yamaha CX5 computer

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One Two Testing - Copyright: IPC Magazines Ltd, Northern & Shell Ltd.

 

One Two Testing - Oct 1984

Donated by: Colin Potter

Scanned by: Mike Gorman

Feature by Ben Duncan

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