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Author Topic: You remove ground loop roll with a 3 prong to 2 prong adaptor what next...  (Read 6941 times)

John Roberts {JR}

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In the unlikely event that a person contacts both the hot and neutral, and is otherwise insulated from the surrounding environment, a GFCI will not protect against that shock. :o

One scenario where it could happen is if a "grounded" device is plugged into a bootleg ground receptacle, and another "grounded" device is plugged into an RPBG receptacle, and the person contacts the chassis of both devices. A GFCI upstream may not protect from that. Of course, it's likely that the GFCI would trip well before that happens (because of the bootleg grounds), but hey, it's a conceivable problem.
Perhaps a few too many "and thens".

I ASSume you mean bootleg ground to neutral (not RPBG). If the GFCI outlet and normal(?) bootleg outlets are used in parallel (not plugged into each other), the bootleg safety ground connection is effectively on the input side neutral of GFCI protected outlet. In that scenario any line to safety ground (to neutral via input side bootleg) fault current is outside the GFCI loop and will trip the GFCI outlet at the expected >5mA.

As I've warned before, if a GFCI bootleg ground is connected to neutral at the output side of the GFCI, that will defeat the protection for faults to that bootleg ground. If it is bootlegged to the input side neutral the GFCI will work, but still DON'T DO THAT it is always unsafe practice to bootleg.

Better IMO to just float the safety ground and let the GFCI do it's magic. 
 
JR
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

John Rutirasiri

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Mac float all over the place.  The definitely need to be isolated as much as possible.  Fortunately I've not been involved with using one to feed both video and audio.  Just audio, which I fixed with a Radial transformer DI.

I just got back from China and plugging a Mac into the 240VAC mains over there results in leakage on the case you can feel.  This odd buzzing tingle that makes the case feel textured.  One of these days I'm going to get hold of a meter and see what the potential between the case and a real ground is.

We use Apple laptops (yes the aluminum Unibody ones) all the time for video and audio and have not had issues or need "isolation" for VGA, DVI, HDMI, and even the headphone jack on occasion (I use both Radial and Peavey USB DIs.)    The AC adaptor/power supply on Macs can be used with the the 2 prong ungrounded plug (plugs directly into outlet) or the 3 prong grounded power cord.  Which did you use?

John R.
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Alex Thompson

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I've run across plenty of laptops, and owned one, that caused this issue and some audio noise as well.  Almost every time all noise went away when the laptop ran on batteries. Maybe this is the solution rather than disconnecting any safety grounds if you have enough battery life to last through your average event.

Another common fix, although less universal than running on batteries, that usually helps with audio and video noise is a ground lifted DI box connection to the console.



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Alex Thompson
Joy Audio Visual, LLC
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Stephen Kirby

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We use Apple laptops (yes the aluminum Unibody ones) all the time for video and audio and have not had issues or need "isolation" for VGA, DVI, HDMI, and even the headphone jack on occasion (I use both Radial and Peavey USB DIs.)    The AC adaptor/power supply on Macs can be used with the the 2 prong ungrounded plug (plugs directly into outlet) or the 3 prong grounded power cord.  Which did you use?

John R.
Typically when traveling we just carry the two prong adapter that goes right on the PS.  I'll bring the 3 wire cord and a travel adapter next time and see if I can still feel the leakage.
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John Roberts {JR}

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Typically when traveling we just carry the two prong adapter that goes right on the PS.  I'll bring the 3 wire cord and a travel adapter next time and see if I can still feel the leakage.

If you can feel it you can measure it with a VOM... I measured close to 120VAC and 2 mA leakage from my power strip with the broken surge protection circuitry to a real ground return.

JR
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

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