Most musicians really don’t want to learn about electrical engineering, or even how basic electricity works. Everyone, however, should learn how to test for and avoid electric shocks on the stage.
Guitar amps and mixing boards as wired from the factory are inherently safe, but they can become silent-but-deadly killers if plugged into an extension cord or wall outlet that’s improperly grounded. This is because guitars are held in moist hands while wet lips are touching another electrical circuit, the microphone.
It’s up to sound techs – and musicians – to make sure a guitar or microphone is never electrified due to poor maintenance, bad connections or a broken-off ground plug. The so-called “Hot-Chassis” problem is what causes a tingle or shock when you touch the mic with one hand or your lips while holding a guitar with your other hand. The cause is that a chassis has become “hot” through a wiring fault.
What Is This Volts Thing?
What’s so hard to understand about electrical shocks in general is that they don’t seem to happen for any obvious reason. For instance, you can watch a pigeon on a power line that’s not being shocked, yet sometimes just holding a guitar while standing on wet ground can bring you to your knees. Why is that?
The first thing to understand about electricity is the concept of voltage. Think of voltage as electrical pressure, just like the pressure in a tank of water.
Now in a tank of water we measure pressure in something called PSI (pounds per square inch), which will, of course, increase if we get a deeper tank. This pressure is caused by the pull of gravity from the earth and if you hook up a hose to the tank, the water will flow toward the ground.
So while 10 PSI of water pressure from a short tank might give you a trickle of water when hooked up to a hose, 100 PSI of water pressure from a really tall tank gives you a stream that will spray much farther (Figure 1).
Water – and electricity – tries to flow to the side of least pressure. You can imagine that if a pipe is connected between two tanks with exactly the same water level and pressure (say, 100 PSI) there will be no flow of water through the hose.
It just sits there and does nothing because the system is equalized. However, if you connect one tank with 100 PSI of water pressure to another tank with 10 PSI of water pressure, water will flow from the high tank to the low tank. We measure this water flow in gallons per minute (Figure 2).
The same thing happens with electricity. You’ve often heard of “completing an electrical circuit,” but think of it as pipes between different electrical pressures.
Getting back to the pigeon on the power line, if both of the bird’s feet are on the same wire, they’re at exactly the same electrical pressure. Because they’re at the same pressure, there’s no electrical current flowing through the bird.
If, however, the pigeon is unlucky enough to touch one foot on a power line and a wing to the grounded metal power pole, then his foot will be at 1,000 volts (think PSI of water pressure) and his wing at 0 volts (think an empty tank with zero pressure).
This will cause a lot of current to flow through the bird, which we’ll measure in amperes. And indeed, 1,000 volts across a pigeon can cause a bird explosion.
Hot Chassis Shock
Now, consider a guitar. Sometimes you may feel a shock when you touch one hand on the guitar with the other hand on the mic.
What’s happening is that there could be an electrical voltage (think pressure) on the strings of your guitar, which is waiting for some different electrical voltage level to head towards. If your entire body is at the same voltage, then like the pigeon every part of you is at exactly the same voltage. And like the pigeon, there’s no current flow and you feel no shock.
However, if your one hand is on the mic at essentially zero volts and your other hand is on your guitar at 120 volts due to a wiring problem, you become the pipe and the different electrical pressure (volts) will push current (amps) through your hand, arm and chest cavity, then out through your other hand.
If your hands are dry, there might be so little current flow that you might not even feel it. But put a damp hand on your guitar strings and wet lips on the mic and you’ve made a good connection from the power plug of your guitar amp to the ground of the PA system.
In the case with an ungrounded guitar amp, a lot of current will flow through your body, which you’ll quickly recognize as a shock and potentially an electrocution.
Heart To Heart
The dangerous part of shocks is when this electrical current flow goes through your chest cavity since right in the middle of you is your heart, and hearts don’t like to be shocked. That’s because your heartbeat is controlled by electricity which comes from your own internal pacemaker.
And just like a clock radio can be scrambled by a nearby lightning strike, even a small amount of electricity passing through your heart can cause it to start skipping beats and cause a heart attack. Just how little? I’m glad you asked.
Many of you have likely seen the 20-amp marking on a circuit breaker. That means it can supply 20 amps of current flow when asked to do so. Again, think of it as gallons per minute of flow, and amps are indeed a count of electrons per second flowing through a wire (think pipe).
Much more on that later, but it takes less than 5 milliamps of current to cause your heart to go into fibrillation mode. That’s just 5/1000 of an amp or 0.005 amps of alternating current to cause what’s essentially a heart attack. It takes just 30 volts of alternating current (AC) to stop your heart if your hands are wet.
On the strange-but-true side of the coin, while 60 Hz AC is what comes out of a standard electrical wall outlet) can cause your heart to go into fibrillation and stop pumping blood, the emergency rescue crew will use direct current (DC) of several hundred volts to reboot your heart and get it beating regularly again.
That’s what they’re pushing through the paddles placed on your chest – direct current from big capacitors like you see charging on the TV dramas before they yell “Clear!”
Play It Safe
The first rule of staying safe from electrocution is to keep your heart out of the current flow. You can see that getting shocked from hand to hand or hand to lips or feet is about as bad as it can get.
That means if you’re plugging in a guitar amp with one hand, the last thing you want to do is hold onto the metal rail around the stage with your opposite hand or be kneeling on the wet ground. If you have two points of contact and something goes wrong (like you touch a bare wire), the current will flow to your opposite hand or feet, passing through your heart in the process.
So always use just one hand when plugging or unplugging power cords for amps. Not doing so is to invite death by electrocution, and, really, who wants that?
Take a look at a typical 120-volt grounded wall outlet, shown in Figure 3. The top half of the illustration shows the sideways slot of a 20-amp outlet, while the bottom half shows a more common 15-amp outlet. In both versions you’ll see a Hot connection (the short blade), a Neutral connection (the tall blade), and a U-shaped Ground connection (called the safety ground).
Those ground blades are on the power outlets and plugs for good reason. If something goes wrong internally with the amp (say a wire shorts to the chassis or a power transformer gets leaky), that ground blade is supposed to divert the voltage from the strings of the guitar through the ground in the power panel, which will then trip the circuit breaker.
If the circuit breaker doesn’t trip because you’ve eliminated the safety ground by breaking off the ground blade of your power cord, then you may have an electrically hot guitar or microphone in your hands. And you may not realize it’s electrically hot until you touch something else that’s grounded with your other hand or lips, just like the bird holding onto the power line with his feet doesn’t get shocked until his wing touches the grounded metal power pole. Then it’s lights out!
So if you circumvent that safety ground by cutting off the ground blade or using an adapter plug like you see on the left in an attempt to stop hums or buzzes in the sound system, you can put your heart in the middle of the ground path and risk your life every time you plug in an amp.
Don’t do it. Always ground amps and PA system equipment properly.
No Shock Zone
By grounding every amp and mixer in your sound system properly, you will help create a “No Shock Zone” on stage, making it a safe place to perform without fear of getting shocked or electrocuted. So take this seriously… if you or anyone in the band is getting shocked by a guitar or mic on stage or even in your practice basement, now is the time for action.
• Use only one hand to plug or unplug any power cables for your amps.
• Don’t cut off the ground blade of an amp or mixer power plug to stop a hum in the PA.
• Never stand or kneel on wet ground while touching a guitar, keyboard or microphone.
• If you feel a shock on stage, avoid further contact until you can determine the source of the problem.
Note: This article is provided as a helpful educational assist with sound system setup and musical performance and is not intended to have you circumvent an electrician or qualified audio technician. The author and ProSoundWebg will not be held liable or responsible for any injury resulting from reader error or misuse of the information contained in this article. If you feel you have a dangerous electrical condition in your PA system or instruments, contact a qualified, licensed electrician or audio installer.