Info On Power

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I good, basic look at power and how it affects your studio.

Taking the chance that there are a few who haven't had a lot to do with electricity, here are a few facts, etc. that everyone hooking up gear should know.

Source power:

Any electrical/electronic gear is going to use a certain amount of wattage, or power. It is usually spelled out on a sticker or plate that gives the input voltage, frequency or Hz, amperage, and watts. The watts is the important one as that IS what will be consumed. Watts equals (roughly) volts times amps. If you have a 120 watt light it will use one amp. 120v X 1a = 120Watts.

If the voltage is less than 120, the amps will go up to make up the 120watts.

Voltage up, amps down. Volts down, amps up. The gear uses watts, not volts or amps. So, if you use a 14 gauge wire (rated 17 amps max) for a 15 amp circuit, but you have only 109volts from the socket, the amperage will be more than 15 amps. It will exceed the 17 amps rating of the #14 wire and it will melt the insulation and short out, hopefully tripping the 15 amp circuit breaker for the building circuit you are plugged into. Lesson: Use #12 wire for all power cables to your gear unless you know for sure the voltage is a reliable and steady 120volt source.

Power supplies, surge suppressors, and line conditioners:

Audio gear is expensive, even the cheap stuff. It's also sensitive to fluctuations of voltage, surges caused by lightning or heavy equipment starting up, etc. The surge strips you buy for $10 at WalMart are OK for PCs because PCs use a specially designed power supply that protects against brownouts, shorts, surges, etc. But, the surge strips aren't worth a flip for a mixer that doesn't use a switching power supply, or a bank of power amps with fuse protection only. Also, when these surge strips do encounter a surge, the varistor that is the protection burns out, but the power keeps coming. You don't even know that it isn't protecting anymore unless it's one of the better units with an indicator.

To protect audio equipment properly and safely, an Isolating Line Conditioner is needed. This unit has a transformer that doesn't change the input voltage, but simply isolates the incoming power from the load with coils of unconnected windings. It also employs solid state "crowbar" circuitry that will soak up a surge of voltage, like lightning, or unrelated equipment loads, and store that extra power to give back if a brown out or severe voltage drop occurs. Essentially it maintains the input voltage within .1%. That's 120V +- .12V, or 119.88 - 120.12Volts. Very tight control, very good protection. A 1000KVA unit is standard and rackmountable, and has ten or more duplex 120v receptacles to plug power strips into. That size unit would power a good sized PA, mixer, rack FX, desk lighting, amps, amp stacks, etc. Two of those would do a Who concert.

Voltage drop:

Basically, the longer the wire or cable, the bigger gauge it needs to be. Long cables soak up voltage, which causes amps to increase, which causes heat, and more voltage loss, and, eventually, total loss of signal. 25 feet of #14 might handle 15 amps. But 100 feet of #14 won't handle 10 amps at 120 V. Also, stranded copper is the only acceptable wire type for power cables. Solid wire won't flex and aluminum won't conduct as well.

Ground: Why, Where, and How?

What is ground in an electric circuit? Is it really hooked to the ground? Why do we need it? It's going to take awhile to explain this, so grab a beer or Pepsi, and get comfy.

Electrical potential (volts) is the difference in pressure exerted by the power source on a circuit hot wire compared to the neutral wire. Current (amps) is the flow of electrons in the circuit caused by voltage, and resistance (ohms) is the friction caused by the flow of those electrons in the wire. To make a circuit work, there must be a difference in the voltage at the beginning of the circuit compared to the end of the circuit. If you have two wires, one with 120 volts and the other with zero volts, you can put components between the wires and voltage will push the atoms through the components causing work to be done.

"Well", you say, "any wire not hooked to anything will have zero volts. Will that make a circuit work?" No, it won't. Both wires have to have the same source or reference location. When the power station generates electricity, it does it with magnets spinning inside a bunch of wire. The magnets are on a shaft that is held by bearings, in a housing, bolted to the concrete floor, poured on top of, the ground. The magnets push electrons out of one molecule and into another, which bumps those electrons out and into another, and so on, all the way through the conductive wire, until it reaches back to where it started, the ground under the power station. That ground is in contact with the whole Earth, so anywhere it can get back to continuous Earth will complete the circuit. Both the power house foundation and equipment, and the end of the circuit have the same reference or source, Earth. But the wire from the power station has electromotive pressure (volts) from the magnets pushing electrons around but the end hooked to ground has no pressure. There is a difference so the circuit will work.

If you had two wires from the station, each with the same volts, a circuit wouldn't work between those wires. Two wires hooked to ground, same thing. No circuit. There must be a difference to have voltage. Try putting both leads of a voltmeter on the same end of a battery. Read anything on the meter? Now read from one end of the battery to the other. Anything there? Of course there is. Hook a voltmeter to two wires each having 380,000 volts and you will read zero.

But grab one of those wires while barefooted and see what happens. A circuit needs two wires normally known as Hot and Neutral. Hot has pressure, neutral does not, but both have the same reference source.

The Earth ground is the common reference for practically all generated power in the world. A good electrician will check for voltage on a wire by first checking that wire and the second wire of the circuit, then checking that wire and any neutral in the power panel, and, finally, that wire and a solid Earth grounded wire or cold water pipe, anything conductive that goes into the ground. Only if it reads zero in all cases can he safely say there is no power there.

Some who are familiar with electrical circuits might say, "The neutral wire in a 120VAC panel is grounded, so neutral is a ground wire." Yes, and no. We could have run a wire all the way back to the power station foundation and used that as the neutral reference. It would be grounded but in electrical systems a neutral does not serve the same purpose as a dedicated ground wire. Neutral is necessary to complete the circuit. Dedicated ground wires are for safety purposes and are not necessary for the circuit.

So, what's the big difference? The neutral AND ground wires are grounded, why aren't they the same thing? The difference is how each is used in the system, and where each one connects to ground. Look in a normal residencial breaker box on any house and you will see a neutral bar and a ground bar in the bottom of the panel. You will also notice a bare wire going from each of those bars to a single copper rod driven into the ground below the panel. That is the end of the similarity. White neutral wires from the house are all connected to the neutral bar and each white wire should be paired with a black or red wire coming from a circuit breaker. A bunch of green or bare wires from the house hook to the ground bar and there maybe a lot more of them than neutrals or circuit breakers as there is no direct corellation between grounds and hot or neutrals. From those two bars on into the house, the neutral and ground wires never meet again, and are not used for the same thing.

So, why do we need both a neutral and a ground? A neutral completes the electrical circuit. A ground wire provides a direct, uninterrupted, low resistance path for any unwanted voltage to be gotten rid of safely. Remember way back, when drill motors and circular hand saws were metal and had a two wire plug? If the motor inside got hot and the insulation melted, the person using that power tool usually was killed by the voltage shorting out to the metal housing and electrocuting him. Black & Decker invented a safer, double insulated series of power tools that had plastic housings, and also had a dedicated ground wire from the motor casing that ran into a third hole in the wall plug, and all the way back to the ground bar and to the ground rod, directly without ever coming into contact with the power wires or tool, or house wiring again. Any melted wire in the tool was no danger to the user anymore. The hot shorted DIRECTLY to ground caused an 1100 percent increase in amperage in 1/100th of a second and tripped that circuit's breaker immediately. Yayyyyy Black & Decker !!

Soon, the National Electrical Code, part of the National Fire Prevention Code, and the Universal Biulding Code required three wire electrical systems to be installed in all inhabited structures. Soon after that, it was required for all permanent power distribution of any kind, anywhere.

Ideally, the ground wire in power systems never sees any voltage or current at all, anytime ever, except in a short circuit of a non-double insulated device, which are very rare devices these days. But, in reality, ground wires soak up almost any magnetic field around and pass the resulting voltage into the chassis of any device plugged into the system, like mixers, PAs, FX components, radios, etc. Where do these magnetic fields come from? Flourescent lights, air conditioner motors, bad sparkplug wires on cars, power transmission lines outside on the pole, power transformers for lighting, and on and on. If one ground wire in a biulding has a lot of magnetic interference, and another one not so much, what do we have then? A difference in voltage of two ground wires. And what does a difference mean? Current flow between them, just like in the power wires. This causes devices on a circuit that uses one of the grounds to have a different chassis reference to ground than a device on a circuit using a different ground. If these two devices are then integrated electrically, like with a 1/4" plug or XLR connector from one to the other, you run the risk of those two devices causing audio interference at least, and total failure to operate at worst. That is why all audio and computer gear in a studio should all be connected to the same ground, and, in most biuldings, that requires them to all use the same power circuit. If you know what to do and how, you could use a bigger gauge ground wire and hook all your studio power circuits to one bigger ground wire and seperate it from all the other grounds all the way back to the breaker panel. But you almost have to be a journeyman electrician to know how to wire that and unwire the other.

Now you know why grounds are, where they hook to, and how they work. Any questions? Just ask.

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User-submitted comments

Feb 28, 2009 03:20 am
good job
thanks for the info.
God bless!!!!!

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