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Re: ? about a Cheater plug to eliminate hum---might this configuration cause "death"?

Posted by StephenJK on April 6, 2007 at 17:30:20

In Reply to: ? about a Cheater plug to eliminate hum---might this configuration cause "death"? posted by jjk12 on April 6, 2007 at 15:19:26:

Isn't it interesting how everyone has an expert opinion. It's like this. Residential power supplies in North America are with a 3-wire 120/240 VAC system. That is, with two "hot" wires and a neutral. The voltage is measured between the two hot wires at 240 volts, and between each hot wire and neutral (or ground if the neutral is grounded) at 120 volts. The 240 volt supply is used for your stove, clothes dryer and air conditioner, the 120 volt supply for everything else. The only reason that the 240 volt supply is used is because power consumption, or Watts, is a multiplication of volts and amps. By doubling the voltage to 240 for the big loads, the size of the supply wires and the breakers can be cut in half.

As the power supply is AC, at 60 Hz, that essentially means that the generator from the utility has the job of moving electrons back and forth 60 times per second.

By code, the neutral is called the "grounded" conductor, the ground wire is the "grounding" conductor. In most jurisdictions, the neutral must be grounded, but at one point only to prevent ground loops. This is generally done at the distribution panel, where it can be easily inspected.

With a stereo system, every power cord will obviously have a hot and neutral wire to provide 120 VAC to the component. Some will have a two-wire connection cord, some will have three. Those with three will have a ground wire connected to the frame or chassis ground of the device.

That being said, the ground path through that device may be at a different potential from the ground of the duplex receptacle that is supplying the power. With a difference in potential, and a resultant voltage rise, this can cause a current through a ground loop that can cause an audible hum.

Lifting the ground of the amplifier by either breaking off the ground pin or using an adapter plug with the ground removed is a well recognized means of preventing or reducing problems with ground loop hum through the speakers.

If this was truly a death defying situation, then why do they sell appliances and devices with only two-pin plugs as opposed to three-pin?

In fact, my Bryston 4B amplifier has a switch on the back labelled "Normal" and "Separ" for separate which lifts the ground pin if there is a ground loop hum problem.

Any risk or danger of electrocution is only possible if the hot wire becomes connected through a major fault to the metal frame or chassis of a component. If that were to occur, with no ground wire, and the grounded neutral wire was through a high resistance, there is a chance of getting a shock. With a separate ground wire connected, the hot wire would have a low resistance path to ground that would trip the supply breaker or blow a fuse.

With stereo equipment, however, the supply power being connected through an isolation transformer or a step-down transformer will introduce a high impedance path that will cause a trip on the primary side only. That is, if your cat chews through the supply wire to your amplifier, the breaker will trip. If something happens internal to the component on the step-down side of the transformer, separate protection is required.

If anyone has concerns about whether a two-pin Hot/Neutral wire is safe or not, just have a look around your house at your floor/table lamps, kettle, toaster, etc.

A ground wire is most definitely a personnel and equipment saving means, but remember, if your electrical supply system was properly installed, the neutral wire is grounded.

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