Wouldn't an isolation transformer eliminate those ground loops?
As you noted, many audio devices have the shields (Pin 1 on an XLR) tied to the audio reference ground when they should be tied to the chassis which is in turn tied to the electrical system ground such that any current on the audio cable shield runs direct to ground and not via the device's audio circuitry reference ground. I think that may be what Sharyn was referencing. Good equipment should be in accordance with AES48 and thus not require a ground lift switch, dropping a conductor at either end or any of the other common 'fixes' in order to avoid ground loops.I agree that the laptop PS are faulty in that way, but I disagree with the above. Tons of pro equipment, the majority, tie the signal ground and the chassis ground together. Most of the good equipment also features a "ground lift" switch or jumper, which floats the signal ground from the chassis. Those switches/jumpers may be misleading as some people think they float the chassis ground (safety ground/earth) which they most certainly do not.
In this situation, the ADAT optical interface is very similar to an opto-splitter/isolator used for DMX distribution, etc. There is no physical connection, so those problems are a nonissue and moot.
As we live in a country where someone sued the mower manufacturer for not telling them to not use the mower in such a manner after being injured while trying to use their lawnmower to trim hedges, regardless of whether you can carry a device or even if it carries itself around on its own, I think the only appropriate assumption is that if the power plug on the device has three prongs then the ground pin is there for a reason and that defeating it increases your risk.So....
(1) If you can walk around with it two prongs are probably o.k. just be careful (Stun guns are two prongs, fit in a pocket, but what a wallop that arc carries).
(2) If you cannot carry it three prongs are needed (and lots of respect).
As we live in a country where someone sued the mower manufacturer for not telling them to not use the mower in such a manner after being injured while trying to use their lawnmower to trim hedges, regardless of whether you can carry a device or even if it carries itself around on its own, I think the only appropriate assumption is that if the power plug on the device has three prongs then the ground pin is there for a reason and that defeating it increases your risk.
What kind of meter did you measure that with? A lot of switching power supplies have caps from the ungrounded and grounded conductors to the grounding conductor. A voltage can be measured but no significant current flows.
I prefer the terminology signal ground and safety ground, as that is really what they are. The reason we have to worry about ground loops is basically because many Electronic Device Designers have been lazy, cheap or simply ignorant and have not properly addressed the path of the signal ground to the safety ground. If that is properly addressed, for example per AES Standard » AES48-2005 (r2010): AES standard on interconnections - Grounding and EMC practices - Shields of connectors in audio equipment containing active circuitry, then ground loops would not be such a common issue for audio devices.
I believe that the important point is having a reliable, very low impedance path to that single earth ground point for the building. Some facilities may use a single ground electrode rod while others use mulitple bonded rods within a small area. And some critical facilities or those with certain soil conditions may utilize a chemical/electrolytic ground electrode rather than copper rod(s).
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