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Author Topic: VGA HUM ELIMINATION  (Read 15942 times)

Brad Weber

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« Reply #10 on: August 10, 2011, 07:26:44 am »

If this is what you are talking about, please don't use these permanently. As I think Brad is pointing out.
Yes.  There was a time when electrical systems had only hot and neutral conductors and relied on metallic plates, boxes and conduit to serve as the safety ground path and the purpose of those adapters is to use the tab or wire on them to adapt modern three wire devices with a dedicated safety ground conductor to those older power distribution systems, the exact opposite of being used to disrupt or break that path.

Devices with two prong plugs are 'double insulated' and designed to isolate the chassis and external surfaces from becoming 'hot'.  However, devices with three prong plugs rely on the safety ground path to address conditions such as an internal short and if that path does not exist then the current has no where to go until something like someone touching the device becomes the safety ground path.  That is why with the potential exception of GFCI circuits under certain conditions, not having a dedicated safety ground path is a NEC violation.

Another common fix for ground loops are 'hum eliminator' devices that go between the device being powered and the receptacle.  These typically electrically isolate the safety ground path between the device and the receptacle until conditions indicate it is needed, at which point current is allowed to flow through that path.  The problem with these devices is that if the current and voltage involved are large enough then the device can potentially fail in a manner that provides no safety ground path.  That is why you probably will not find any such devices that are UL listed.

As it may be the source of much confusion, it should be clarified that lifting the ground of an audio or video signal path, which is what the "ground lift" switch on many audio devices does and which is in many cases a quite acceptable practice, is quite different than lifting the ground of the electrical system. 

John Livings

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« Reply #11 on: August 22, 2011, 03:25:47 am »

As already stated, I agree the adaptor is made to "pick Up" a ground source by using the cover plate screw attached to the brass tab sticking out from the adaptor.

While the tab will help hold the adaptor to the receptacle in place (If you use the screw) thats not why its there.

The adaptors, used properly will enable you to pick-up a ground (If a path Exits) from a two prong receptacle. (Older Systems)

The device is not a ground lift device (although many call it that and improperly use it for that)

Lifting a Ground is a Trouble Shooting Aid only, Not a solution to a grounding problem.

Regards,  John



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« Reply #11 on: August 22, 2011, 03:25:47 am »

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