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Sound Systems: Safety
The dictionary defines safety as: the condition of being safe from undergoing or causing hurt, injury, or loss. Unfortunately, many sound systems are operated with unsafe conditions. We will examine some of these conditions and provide safe alternatives.
Safety is a necessity! 
AC Grounding Most modern sound equipment has an AC power cord with three terminals on the AC plug. Two of the terminals are for actual AC power. The third round one is the ground terminal (Figure 1). It connects the chassis of the sound equipment to the building's electrical ground. The primary reason for grounding a sound system is for safety. A properly grounded sound system will prevent someone from receiving a lethal shock. A secondary reason to have a ground is to reduce external noise pickup. 
Figure 1
The round pin is a ground terminal.
So what can happen if the AC outlet in your school only has a 2 wire AC outlet with no ground terminal? The installer of the equipment may have put a 3-prong to 2-prong adapter (Cheater) on the AC plug and plugged it into the AC outlet (Figure 2). It may have worked for years without a problem. But something may go wrong inside the equipment, or perhaps the AC cord frayed a bit. Somehow, the hot side of the power line comes into contact with the chassis of the equipment.If the equipment had been grounded, the electrical circuit breaker or fuse would have blown. However, now there is no ground connection, and nobody is aware of the danger that is lurking. The first person to grab a microphone and also touch a grounded piece of metal will immediately discover the fault. If they are lucky, they will only receive a mild shock. If they are touching a good ground, they may die. 
Figure 2
Using a cheater to defeat the ground can be very dangerous.
The simple solution is to make sure all your equipment is properly grounded. It may mean spending some money to hire an electrician to check. It may mean having to add some new wiring. But these are small expenses compared to someone's life.
Sometimes, a sound person may intentionally remove the ground connection to reduce hum and noise in the sound system. The hum is usually the result of equipment and/or connectors being grounded in several places, and a ground loop is formed. This article is too brief to deal with ground loops in detail. However, NEVER defeat the AC safety ground on the mixer or any equipment connected directly to the microphones. Microphones need to take first priority in grounding safety. There are methods to provide both safe and ground-loop-free operation. Please call us if you have hum and noise problems. We will be glad to help you achieve a hum-free sound system.
Cables
Sound systems and cables go hand in hand. However, cables can present some safety concerns. Many people have tripped over a cable and hurt themselves, equipment or both. What can be done to improve your safety?
First, use high quality cables. Quality cables will lay flat which means they are harder to trip over. Better yet, temporary cables in traffic areas should be taped down (see Figure 3). Use high quality, cloth gaffers tape that won't leave a residue on the floor, walls, or cables. 
Figure 3
Use high-quality cloth gaffers tape for temporary cables.
Second, take care of your cables. Remove the twists and kinks when you wrap the cables after each use. Your cables will last longer and be safer to use if you spend the time to properly store them.
Wireless Microphones Wireless microphones can also improve the safety of your sound system. They eliminate the tripping potential of cables and are completely safe (there is no AC connection). This is the safest microphone to use outdoors or near water.
Loudspeaker Mounting Another safety hot spot is the loudspeaker mounting techniques. If the loudspeakers could potentially fall on someone, they must be completely secure. The mounting hardware should have a higher workload weight limit than necessary to hold the loudspeaker. The installer's safety motto is: The installer should be so sure of his installation that s/he could sleep under it!
Everyone working with the sound system must be concerned and aware of the potential risks. They must work diligently to avoid and eliminate any hazardous situations. Please call us if you have any questions about safety. We will be glad to check your system and discuss any safety concerns. by Ron Huisinga © 1996 Internet Sound Institute. (www.soundinstitute.com) This article is for personal use only. Any commercial reproduction is not permitted without permission. To obtain permission, contact ISI at hopi@soundinstitute.com
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