10 metres audio cable going into PC = too long?

Does your "perfectly normal" mean:

"there is no fault and no danger (until the ground is actually needed and then will be a danger)"

Thanks to you and everyone else for the feedback. Seems it is less of a problem than i was anticipating.

Actually my cable is not exactly the Maplin one I illustarted but a very similar one.

"Ground" is not all created equal. Dirt sucks as a conductor and you can see significant voltage differences between two grounding electrode systems. If you are connecting signal lines between two buildings be sure you also bond the grounding systems together.

A "ground loop" is caused by having a common ground path for two different signals. Current from each signal causes a voltage drop, due to Ohmic losses, across the ground path for both circuits. The effect is that each circuit affects the signal of the other. Typically if one of those signals is 60 Hz power and the other is something in the audio range, the audio signal will then have a 60 Hz "buzz" on it.

Obviously, if the only ground path is through a common 3-wire socket, yes it is possible for two boxes to have a ground loop.

That is not true. Granted that the 20 Volt differential he mentions in another article is high (for a residential area), it is not at all uncommon.

What is uncommon though, is a person who can actually feel 20 Volts!

Then there would have been no differential, and hence no voltage and no tingling... ;-)

Not a bad thing, just a rather common thing in many industrial areas.

You got this backwards. A ground loop is caused by having two ground paths for a single signal wire. A hum signal is induced into the signal wire by means of a hum current flowing round that ground loop. That current can be generated in either of two ways - a simple potential difference between the two grounds, or alternatively magnetic induction into the loop; generally the first will generate the bigger signal.

The above does describe typical residential power distributionn. However, anywhere that industrial power (i.e., 3 phase) is available, there will in fact be all three phases available...

Same in the US.

That might be, might not be... it would depend on local laws.

Don Pearce spake thus:

Reread my earlier post above. In it I described the situation where a business I once owned needed to have a power converter installed for

I think the converters can be shared, so if a couple or a few neighboring businesses need 3-phase power, they can all use the one converter.

I'm surprised. Just down the road from me there is a small engineering company - they have a couple of mills, a few lathes and assorted other machine tools. The power company didn't even ask - they just got three phase, straight from the street outside.

Actually, what I said was *precisely* correct.

Your language is a mess, but what you just said is *exactly* the same thing. One wire is a common path...

Wrong. There is no loop involved. It is current flowing on the

Get a book or two... and study what happens. Try drawing a diagram of what you think is happening!

Nonsense - you claim one ground path and two signals. It is one signal and two ground paths - it is those two ground paths that form the ground loop.

No, my language is just fine, and it is the exact opposite of what you said.

There is a loop involved. That is why it is called a ground loop. The loop is necessary for the current to flow round and generate the emf that appears on the signal wire.

Thank you, I have designed a great deal of high precision measuring equipment and I know exactly what signal paths are present in a ground loop. And they aren't what you claim.

What is a "converter"? I've never heard of anything described that way.

Virtually all power is generated as 3-phase...

What you actually get merely depends on what the transformer arrangement is. Single phase residential power is nothing other than one phase from a 3 phase distribution system. All that is required to have 3 phase power is *more wires*!

And I have it *precisely* correct. (Hint: I'm not guessing.)

If there were only one signal... what problem would there be???? The trouble is that one signal causes interference with another. It does that because they share a common path. Ohmic losses across that conductor affect *both* signals, even when caused by only one of them. Bingo, that *is* the problem.

Two ground paths and one wire... does *not* make sense. Signals have paths. Those paths can be wires. You can't have two paths in one wire...

But the common "ground loop" is indeed caused by grounding a single conductor at two points. That provides a common path through the single wire... for *two* signals. One is the "desired" signal, and the other is a current between the two ground points.

Try drawing a diagram of what you are describing.

If you do know what it is, you certainly have a problem describing it in terms that make sense. I'll vote for you don't know...

Remember the good old days when everything had a 3-core mains cable? You could get a ground loop just plugging a tape recorder into an amp. The bodger's solution was to disconnect the earth in the mains plug and remember always to connect the audio cable to the amp before connecting the power. Now everything has 2-core power leads so you get tingles.

So what are you saying here - that a mono signal can't suffer a ground loop? Stereo is the minimum that can show the problem?

You only need one signal. Here's a hint as to where you may be going wrong. Signal is the term used to describe the wanted stuff. The rest isn't signal - it is hum.

Of course it makes sense. The commonest scenario for two ground paths is that one is the outer of the coax, and the other is a pair of ground wires in the mains leads, meeting at the mains ground. The single signal wire is the inner of the coax. This just isn't that hard to understand.

No it doesn't. It means that the ground is connected via two separate paths - you need those two separate paths to form the loop.

Done. You can find it here http://81.174.169.10/

No, I think I have described what is going on perfectly - I suspect the confusion is at your end. It may be simply a semantic confusion over what constitutes the signal.

No. It's normal and legal to have a load of double-insulated equipment connected together so the signal ground is floating at roughly half mains voltage and can deliver several mA. It's dangerous, in my opinion.

In the UK, with 240v mains, and adjacent houses on different phases, you might have 220v between the two cables in the attic.

And you can't feel 20v AC unless one end is on your tongue. I just tried it. :-)

Floyd L. Davidson spake thus:

It's a device--a big, honking piece of electromagnetic equipment--that generates 3-phase power from 2-phase power. In this case, it sits in an underground vault beneath the sidewalk, covered by one of them metal plates.

Nope.

Apparently not. If you don't believe me, ask PG&E (Pacific Greed and Extortion, as they're known around here). They don't run all 3 wires as part of their normal power distribution.

I know this thing exists, because I saw the crews working on the damn thing in front of my shop when it malfunctioned and the press stopped working.

I'm stunned. This is the first time I've ever heard of power being generated as anything other than three phase. Apart from anything else, single phase is mega wasteful of copper.