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Old 28th January 2013, 04:02 PM   #33761
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One of the main problems i encounter with leakeage is TV antennas distribution in buildings. Very often the leakage between the ground of the wall TV plug and the eath of the AC is so high that you can have a little shock when you touch the two before you plug them , and see a little sparkle when you connect them togethier.
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Old 28th January 2013, 04:10 PM   #33762
SY is offline SY  United States
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Originally Posted by john curl View Post
So many 'far fetched' conditions had to occur before any serious injury, that extreme measures did not seem to be important enough to consider. You could even suffer a mild 'shock' from a guitar amp, for example, and it was considered OK, so long as it could not be fatal.
Stone the Crows.
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Old 28th January 2013, 04:13 PM   #33763
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About the grounding tip, i suppose we have some norm about hot and neutral, never respected. But norm is severe with earths diameter and impedance. my suggestion was not to modify wall outlet, but what you call "Power distribution units" ? Right ?
The outlets on the power distribution units are just an extension of the wall outlet. So I fail to see what sort of distinction that is.

Also, inside the equipment, switching and fusing should be done on the hot lead. You go and flip hot and neutral at the outlet or some power distribution unit and now your switching and fusing is on neutral, not hot.

se
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Old 28th January 2013, 04:20 PM   #33764
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Yes, but he wasn't talking about doing it inside the piece of gear. He was talking about doing it at the AC outlet.
se
That is US code, where we ground the neutral. Elsewhere they do have a safety ground but both other wires are hot! So some places it is decent practice. (P.S. do resist testing for the hot with your tongue, spend the money on a meter.)


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In general or does that change with primary phase?

Thanks
-Antonio
General case. If you are worried about primary to secondary leakage a foil shield can be used. It works for that when it is connected back to the safety ground. But most modern transformers used for audio do not wind the secondary on top of the primary. They used a split bobbin and wind side by side.
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Old 28th January 2013, 04:21 PM   #33765
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Stone the Crows.
When i was in charge to the french "Audio Analyst" Pa system, i was very upset about this ! Verifying or make verify the AC between guitar amps and our mikes before each performance or rehearsal: we had often to add earth wires to the guitar amps enclosures (some had even a button to disconnect the earth !!!!!)

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The outlets on the power distribution units are just an extension of the wall outlet. So I fail to see what sort of distinction that is.
Steve, I never advertised to modify the Wall outlet, never. The power distributor can-be considered as part of the audio equipment, don't you think ?
It is just to correct the way your audio equipments deal with transformers leakages, witch, as you will see, is not always good. And you are not obliged to do anything, if you don't want to. Not obliged to use C core transformers, as well.
[edit] about fuse and power switch, they deal with currents, and, as long earth is connected, i don't see any inconvenience to set them on neutral or hot as long isolation is correct in the primary of the power transformer.
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Last edited by Esperado; 28th January 2013 at 04:37 PM.
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Old 28th January 2013, 04:29 PM   #33766
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That is US code, where we ground the neutral. Elsewhere they do have a safety ground but both other wires are hot! So some places it is decent practice.
Yes, but he posted it on a forum where a good percentage of the readers are in the US.

se
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Old 28th January 2013, 04:32 PM   #33767
RNMarsh is offline RNMarsh  United States
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This might seem overly simplified but I'll say it anyway because it is a fact: Gounding issues in the home or apartment (potential differences between grnd) are most of the time due to different ground points...... antenna/catv and power not being grounded to the exact same ground point. This is very common in buildings up to the recent past. Codes have been changed for new buildings but that only leaves a hundred million messed up buildings.

Leakage can be checked to see if the products have been UL approved. Old amps of the past used the worst practices.... even connecting hot to chassis via rfi caps to chassis was a common practice.... evenually, with a lot of such equipment in parallel (stage, studio, some home CI) the total combined leakage running thru ground/shields can be a shock! So, even though a product has UL approval on leakage et al, the total leakage on the neutral/grnd can become worrysome even if there is a lot of "OK" products. But, the new products normally in the home (DVD etc) are double insulated and leakage is in the microAmps for them.

Note: Large stage systems in USA for concerts also use 230V balanced power. The power draw is too high for 120v only system. In CI homes, balanced power is often done now via balanced power transformers.... and it is legal under NEC to do so.

Thx--RNMarsh

Last edited by RNMarsh; 28th January 2013 at 04:44 PM.
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Old 28th January 2013, 04:41 PM   #33768
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In 1962, we were safety testing a Fender Bassman amp. I told the head of UL about how Fender amps could shock you, if you played in wet weather. I was told that the 'caps' where the leakage currents come from were small enough not to kill. Of course, I had been shocked on someone else's Fender Amp, when we played outside, once, so I knew that it could be VERY UNCOMFORTABLE, if not dangerous. I didn't win the argument.

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Old 28th January 2013, 04:42 PM   #33769
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I never advertised to modify the Wall outlet, never. The power distributor can-be considered as part of the audio equipment, don't you think ?
No, I don't think a power distributor can be considered part of the audio equipment. It is an extension of the AC mains.

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It is just to correct the way your audio equipments deal with transformers leakages, witch, as you will see, is not always good. And you are not obliged to do anything, if you don't wan to. Not obliged to use C core transformers, as well.
Yes, but you need to realize that not everyone reading your post lives in Europe.

We have a 220 volt system here with the safety ground tied to the AC distribution transformer's center tap so that the safety ground can be used to return fault currents from either side.

However we only use 220 volts for heavy appliances like electric clothes dryers and such. The rest of our homes are wired for 110 volts which taps off one side of the AC distribution transformer and the center tap. That gives us a hot and a neutral and the safety ground is tied to neutral back at the service panel (the main panel where the power enters the home).

So for safety purposes, it's critical that hot and neutral don't get flipped around.

se
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Old 28th January 2013, 04:46 PM   #33770
bcarso is offline bcarso  United States
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I probably related the story of a three-piece Harman powered speaker which had a two-wire polarized mains cord. By design the internal transformer primary floated with respect to anything else except hot and neutral, and hot was switched.

A complaint came in that was passed to me that the product was a safety hazard and defective, and a stop ship to Microsoft was advised. My boss said something to the effect that he'd seen things like this before, and it would turn out to be someone who'd modified the unit improperly and was now trying to cover his tracks, and not to worry. He had requested the unit be shipped back for analysis.

I finally saw the emails. The discoverer of the supposed defect was one other than Keith O. Johnson! I advised my boss that this was someone to be taken very seriously indeed.

As best we could reconstruct it, and after conversation with KOJ, it seemed that his particular sample had somehow managed to sustain a short circuit between a.c. neutral and the system common! AFAIK this was a singular event, and the best that could be conjectured was that a bracket had been misinstalled, and instead of being retained by the plastic housing had gotten wedged into a place that accomplished the errant short. Unfortunately in disassembling the unit Keith had destroyed the evidence, and had wound up concluding that the neutral-common connection was intentional!! Of course in virtually any installation, but especially those with a safety-ground-referenced signal source (e.g. a computer sound card) this would at the very least occasion huge amounts of hum and noise.

But for those installations somehow with hot and neutral reversed, it could be catastrophic. And in Keith's case he had his Pacific Microsonics DAC as a source, and was using balanced power (was it Equitech?) for mains. So hot and neutral had ~60VAC on each relative to safety ground. The speaker promptly blew out the DAC. Ouch.

I was able to persuade him that in no way was this issue related to the design, other than in terms of failing to anticipate the possibility of misassembly. We instituted a test on the production line for verifying high resistance between mains in and signal common. But as far as I know this was a singular defect, yet one that found its way into the hands of a singular person!
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