Hello John Beck,
While your concerns about safety are well noted, I am describing a very common practice in the analog audio and video days, for decades. I never got shocked, and to the best of my knowledge, neither did any of my colleagues. I will repeat that your concerns about safety are notable and not to be taken lightly. However, there are thousands of safe devices manufactured and sold every year even in todays markets that do not have 3 prong plugs. They have 2 prong polarized plugs.
I have an electrician's 3 prong tester in my kit of tools, to ensure, first off, that the wiring in a room has correctly wired plugs. It is not all that uncommon for an electrician to get it wrong, which can also be quite dangerous.
I am not advocating removing ALL paths to ground, just duplicative ones which create loops that can cause interference.
I love audio optical and network fiber interfaces due to the lack of any electrical connection between equipment, and the elimination of noise through digital encoding.
There are some converters/extenders that transmit HD video over Fiber, that would be a great way to electronically isolate a problematic bay. I don't have personal experience with one to make recommendations, or an idea of cost, but it is an uber-safe way to solve the issue of ground loops.
Also, I have seen broken shields on coaxial wires still work, due to common grounds via devices interconnects or power, already creating a common ground. The cable with a broken shield still passes a signal due to multiple common grounds. It just allows injection of noise and hum, due to the lack of a complete shield on the center wire. I have also seen RF and high frequency digital signals still pass in a cable with a broken shield as well, just less reliably.
YMMV
Dave Hogan
Burbank, CA
On Saturday, April 25, 2015 10:44 AM, "John Beck jb30343@windstream.net [Avid-L2]" <Avid-L2@yahoogroups.com> wrote:
Sometimes it's enlightening to use an AC voltmeter to check the
potential between various grounds. Ideally, any two chassis grounds,
any two neutrals and any neutral to ground in your entire system will
have 0V between them. Often, this is not the case. --J.B.
jonathansabrams@yahoo.com [Avid-L2] wrote:
>
>
> ---In Avid-L2@yahoogroups.com, <mactvman@...> wrote :
>
> A ground loop is simply an added path to ground, which creates an
> antenna loop, and you get noise generated from any electrical signal
> in the vicinity, mostly the AC mains. You probably already know this.
>
> John - The above text is fine.
>
> Get a bucket of those old adapters that take a 3 prong grounded plug
> and allow it to be plugged into a 2 prong plug. Put those on all your
> gear, except for a primary component, and they all share the same
> ground, through the wires connecting the equipment. (better than just
> cutting off all the ground plugs on your power cords).
>
> John - Please do not do what Dave wrote above! This is dangerous.
> Devices that have 3 prong plugs have them for a reason. What is that
> reason? Safety! If you lift the third prong (ground), you have just
> defeated the electrical safety mechanism of the device in question.
> For those of you thinking, "The device has a fuse", I counter withe
> question "Which device will die first? You or the fuse?" The answer
> is you.
>
> Used to have to chase this in audio studios when they were all analog.
> Just put ground lift plugs on everything except a primary piece of
> gear, like the Switcher or Audio console. I use the ones that have
> polarity blades, so that I don't end up pumping full power down to
> ground....You'll know when that happens when the lights go out, and
> things go spark!
>
> Dave - Did anyone using that equipment ever get injured from a shock?
> Consider yourself lucky if they did not. This is not the proper way
> to solve the problem you described.
>
> You also have to make sure that nobody made bum cables (Audio XLR
> mostly) which swap the ground and hot leads.
>
> John - This is true and easy enough to check with either a continuity
> tester or by opening the connector shell and seeing which leads are
> connected to which pins.
>
> Only other thing that can cause an issue is if your have a shield
> loose on a video cable. Check continuity on the shields.
>
> Dave - If the shield on a coax cable was compromised, would you have
> any signal at all? The circuit wouldn't be completed with a broken
> shield.
>
>
>
>
potential between various grounds. Ideally, any two chassis grounds,
any two neutrals and any neutral to ground in your entire system will
have 0V between them. Often, this is not the case. --J.B.
jonathansabrams@yahoo.com [Avid-L2] wrote:
>
>
> ---In Avid-L2@yahoogroups.com, <mactvman@...> wrote :
>
> A ground loop is simply an added path to ground, which creates an
> antenna loop, and you get noise generated from any electrical signal
> in the vicinity, mostly the AC mains. You probably already know this.
>
> John - The above text is fine.
>
> Get a bucket of those old adapters that take a 3 prong grounded plug
> and allow it to be plugged into a 2 prong plug. Put those on all your
> gear, except for a primary component, and they all share the same
> ground, through the wires connecting the equipment. (better than just
> cutting off all the ground plugs on your power cords).
>
> John - Please do not do what Dave wrote above! This is dangerous.
> Devices that have 3 prong plugs have them for a reason. What is that
> reason? Safety! If you lift the third prong (ground), you have just
> defeated the electrical safety mechanism of the device in question.
> For those of you thinking, "The device has a fuse", I counter withe
> question "Which device will die first? You or the fuse?" The answer
> is you.
>
> Used to have to chase this in audio studios when they were all analog.
> Just put ground lift plugs on everything except a primary piece of
> gear, like the Switcher or Audio console. I use the ones that have
> polarity blades, so that I don't end up pumping full power down to
> ground....You'll know when that happens when the lights go out, and
> things go spark!
>
> Dave - Did anyone using that equipment ever get injured from a shock?
> Consider yourself lucky if they did not. This is not the proper way
> to solve the problem you described.
>
> You also have to make sure that nobody made bum cables (Audio XLR
> mostly) which swap the ground and hot leads.
>
> John - This is true and easy enough to check with either a continuity
> tester or by opening the connector shell and seeing which leads are
> connected to which pins.
>
> Only other thing that can cause an issue is if your have a shield
> loose on a video cable. Check continuity on the shields.
>
> Dave - If the shield on a coax cable was compromised, would you have
> any signal at all? The circuit wouldn't be completed with a broken
> shield.
>
>
>
>
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Posted by: Dave Hogan <mactvman@yahoo.com>
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