Eliminating hum

01-02-15: Bojack
Using cheater plugs is completely safe and often effective.

Don't let the underwriter of your homeowner's policy see that post :-)

Assuming the equipment is in good physical condition, so that there is little risk of an internal short developing between a "hot" AC wire and chassis, the risk that is entailed by the use of a cheater plug is extremely small. However, it cannot be said that the risk is zero. And if that very small risk were to ever materialize, perhaps because the component was marginally designed with respect to how the internal AC wiring is routed relative to nearby sources of heat within the component, or perhaps because the component was wired on a Friday afternoon by someone who was in a hurry to leave, or for whatever reason, the result could very conceivably be either a fire or electrocution.

Yes, use of a cheater plug is "often effective." However the third prong is provided on AC plugs and outlets for a reason. A claim that use of a cheater plug is "completely safe" is, frankly, misleading, potentially harmful, and nonsense.

Good comments by the others. Regards,
-- Al

01-03-15: Grannyring
If a power cord would have a short to the chassis would'nt that trip a breaker in the home?

Hi Bill,

The purpose of the AC safety ground connection (which is what a cheater plug defeats) is to make that happen. Since equipment having 3-prong power plugs connects AC safety ground (the cyclindrical third prong) to chassis, a short between AC "hot" and chassis will cause a very large current to flow through the circuit breaker, resulting in the circuit breaker tripping.

If the AC safety ground connection is defeated with a cheater and that kind of a fault occurs, what is likely to happen is that the 120 volts will cause a current to flow through the shield and/or the return conductor of an interconnect cable to another component, and through that component's AC safety ground back to the service panel. However, depending on the design of the grounding configuration within each of the components a significant impedance, perhaps 10 or 20 ohms or more, will often exist (and should exist, if the equipment is well designed) between the circuit ground and the chassis ground/AC safety ground of each of the components. Chances are good that that resistance will be high enough to reduce the current flow to an amount that is too small to cause the breaker to trip.

In that situation what is likely to happen is that the interconnect cable will get very hot, creating the possibility that it might either go up in flames or ignite whatever it may be in contact with, such as a carpet. And of course the chassis would present a shock hazard to anyone who touched it.

Al, most amps are grounded at the first reservoir cap in the power supply etc...

That doesn't change what I have said, as that involves the amp's circuit ground, not AC safety ground.

BTW, I should add to my earlier mention of ways in which AC "hot" can become shorted to chassis the possibility of a short developing in the power transformer of a component.

... it will at least help you understand if it is a ground loop issue.

Agreed. Using a cheater plug temporarily as a diagnostic tool can be useful, and entail negligible risk.

It is also reasonable to say many things we do every day are far more risky. Things like riding a bike, taking a walk, ice fishing, etc...

Agreed. But it is each individual's call. My point, though, is that a statement that using a cheater is "completely safe" is misleading and incorrect.

Best regards,
-- Al