Landmines

The Audio Component / Multiple Outlet / Dedicated Line Landmine - So easy to Avoid

 

Background - In most all homes in North America, the electrical components we use are powered by a 240/120 Volt Single Phase System.  The illustration to the right shows how the voltage coming into a home is split into two phases, 120 Volt Phase A in Red and 120 Volt Phase B in Black. Inside the 

breaker box, each of those breakers represents either a 120 Volt Phase A or

a 120 Volt Phase B power line.  Both phases are equally suitable in their intended

use, so the receptacles in your home are fed power from one either Phase A

or Phase B.  As the illustration shows, the two phases are 180 degrees out of

phase.  To supply 240 Volts to power large appliances such as a water heater

or clothes dryer, the two 120 Volt lines are combined to supply power to one

240 Volt receptacle.

 

The electricians who designed the wiring scheme and wired up your home did so with two essential goals - 1) make the potentially lethal voltages safe for household use and 2) balance the power loads from Phase A and Phase B power lines throughout the home. By doing so, the breaker box is more or less equally "taxed" as your home consumes power. 

 

Balancing the electrical load between the two phases conflicts with providing quiet power to an audio system.
 

If your audio system is connected to multiple receptacles using the standard wiring your house was built with, chances are the different receptacles near the audio system are split between the two phases. And if you had an electrician install multiple dedicated 20 amp lines, chances are he went with his training and balanced the new receptacles between the two phases. The conflict arises from some components of an audio system being plugged into phase A receptacles and others into Phase B receptacles, which can introduce unwanted noise on the safety ground. Remember, the two phases of receptacles are 180 degrees out of phase. Due to many variables involved in delivering power to your house and finally the breakers, there will be an asymmetry in how each phase sine wave appears.  How much or what type of asymmetry is impossible to say, but it will probably vary throughout the day. Any deviation in how the sine wave appears from regular will result in a small amount of current being inducted onto the house safety ground.  Aside from being an electrical safety net, the safety round is also something like a noise depository for the AC line. Typically, this is not a problem as lights and heating elements or motors are not adversely affected by some small amount of current on the safety ground. However, with single-ended stereo equipment (meaning any device that is not a genuinely differential circuit component), ground is also part of the music signal, so ANY noise present on the ground will also be part of the music signal. And while balanced electronics are better suited to reject this noise, and they too are susceptible.  The ONLY way to eliminate this particular noise problem is to ensure that every component is plugged into a receptacle of the same phase, either A or B, but the same.

 

To avoid this landmine, have an electrician come in and identify which phase the various AC receptacles in your sound room originate and only plug your system into those from the same phase.  Alternatively. the electrician can also configure the receptacles to all be on the same phase. For those who go to the length of installing the dedicated 20 amp lines, ensure that your electrician feeds all dedicated lines going to your stereo system from the same phase, either A or B.

 

It's a problem, but one that's easily avoided.

On the topic of easily avoided issues, let's look at installing an aftermarket receptacle. Please make sure to follow your local electrical code requirements. For example, the standard 15 amp feeder lines throughout your house are probably wired with a 14 gauge Romex cable, and installing a 20 amp receptacle on that line is most likely against code. The reason is not that there is a problem connecting a 15 amp device into a 20 amp connector.  It's against code because of the intended use of that type of receptacle. If one were to plug an actual 20 amp electrical device into that receptacle, with the assumption it is a 20 amp line, and during its operation that device drew current intended for a 20 amp service, it could very well overtax the 15 amp wiring, causing thermal stress to the Romex that is beyond its safety margin. This could result in a fire somewhere along the Romex inside your walls. The electrical code is (usually) about safety first, and it is written to prevent devices from getting connected where they should not. Granted, there is not a problem when plugging in a 15 amp audio component into that 20 amp receptacle that has 15 amp wiring connected to it. But if a fire did occur, the fire inspectors could get you for a code violation that could conceivably void your fire insurance. If you are selling your house and you have 20 amp receptacles on 15 amp lines, make sure and change them back to 15 amp receptacles to avoid any confusion and potential legal trouble with the new owners. Or, you can avoid this problem by having 20 amp lines installed, which go famously well with those cool 20 amp receptacles!