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Isolation transformer

That is a good point. That is why some appliances are given a "hipot" test, or an insulation breakdown test. They should also be checked for good ground integrity by using a bit of current, perhaps 1 to 10 amps, and check for negligible voltage drop.

With isolation transformers, it is important to remember that there is almost always some capacitance from the primary to the secondary (and core), and thus some current can flow with AC applied, and a circuit (=path) to ground on the isolated secondary side. This can be minimized by using split coil bobbins or electrostatic shields, and of course the core and frame of an isolation transformer should always be well grounded.

There was quite a discussion a while back (probably on SED), about safe voltages and how much current is required for electrocution. It is in fact highly variable and depends on many factors. 50 and 60 Hz AC is unfortunately just about "perfect" for causing heart fibrillation, and apparently it doesn't take more than a few mA if the path goes through the heart. So a shock received from one hand to the other is likely more dangerous than one from a hand to a foot. But that is another discussion...

Be safe,

Paul

Reply to
Paul E. Schoen
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"Homer J Simpson"

** Bull.

There were hundreds of TV set models sold in Australia that have a live chassis or a partially live chassis.

EG:

I have a GE brand ( Made by Thompson ) portable CTV with the entire chassis live.

The tuner module incorporates a mains voltage isolation balun, for the TV antenna.

The set has no AV ins or outs of any kind.

Even the two small, oval loudspeakers inside are LIVE !!

........ Phil

Reply to
Phil Allison

** It is technically spot on and the only advice you needed.

I see you STILL have not followed it.

Now, go back to perusing your kiddie p*rn.

ARSEHOLE !!!

..... Phil

Reply to
Phil Allison

OK, Phil, I'll give you one more chance to explain why knowledge of what an electric circuit is is where my understanding failed.

Tell me what is the completed circuit when I touch the top of a charged Van de Graaf generator, or wouldn't I get a shock?

jack - who finds it much more pleasant to be polite.

Reply to
spamfree

" JACK SHIT "

** Go drop dead - you asinine, autistic old fool.
** Go try it.

Hope you enjoy your heart attack - SCUMBAG .

...... Phil

Reply to
Phil Allison

"Isolation transformers need only be used when working on a live chassis item.

Otherwise, you do NOT need one and using one INCREASES the electrocution hazard for a technician.

~~~~~~~~~~~~~~~~

** WRONG !!!!!!!!!!!!!!!!!!!!!

It is a lethal POS that kill technicians.

God , how I hope YOU are the next one

...... Phil "

So which is it? A needed safety device, or a useless killer. You don't seem to be able to settle on a story. But then that's one of the effects of brain stimulants. jack

Reply to
spamfree

So "** WRONG !!!!!!!!!!!!!!!!!!!!!" doesn't mean wrong in your pill addled mind, Phill Pill?

It's either a simple precaution, or it's not. Make up your mind, if you can find it. You were emphatic (20 odd exclamation marks) that it was never a simple precaution. And I thought you were just pissed... PLONK!!! jack

Reply to
spamfree

The entire world is too complicated for an anencephalic, ASD f***ed dung pile like this " JACK SHIT " scumbag to ever fathom.

So he doesn't - and never will.

The VILE TURD is yet another public menace.

....... Phil

Reply to
Phil Allison

Thanks Bob, I thought that's where it used to be. The new version I have has moved it to the VIEW menu, cheers, jack

Reply to
spamfree

In (Free) Agent, go to the Message menu and click on Fixed Pitch Font.

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

formatting link
Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

Reply to
Bob Masta

If you isolate the device from the line via a transformer then, connect the chassis to a real ground. it will protect you in the handling of the device. years ago, old things like radio's used the line voltage directly with a non polarized plug, one side was normally connected to the chassis. If you didn't first test the condition, you could get knock on your butt. By using a Isolated transformer, you can simply connect the chassis to a real earth ground after it, with out any problems of line shorting.. This way, you were protected with a real ground and don't take any chances of causing a line short..

P.S. Take note that many do not know the difference between and autotransformer and a real isolated transformer.. You do not want to use an auto transformer..

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Reply to
Jamie

Circa Sat, 05 May 2007 21:23:34 +0900 recorded as looks like snipped-for-privacy@spam.heaven sounds like:

It appears your question has been answered and understood, but just to reiterate, the isolation transformer ISOLATES the secondary voltage potentials from ground. IOW, it makes it unlikely that one might unintentionally close a circuit across one's body, provided only one hand ever comes into contact with the device under test.

The term "open circuit" (to me, at least) refers to a condition of a circuit that has been designed to be routinely opened and closed, or one where some defect has caused the circuit to be opened. (Very strictly speaking, when a circuit is opened, it is no longer a circuit - it's an air gap. :-)

The point of the IT is to make the inadvertent closing of a circuit across one's body parts more difficult.

Other uses of isolation transformers:

1) Isolating oscilloscope and other test instruments from the device under test, so that potential ground loops that might interfere with the observations are eliminated. 2) Protecting personnel and test and telephone equipment from GPR (ground potential rise) conditions when working at or near a power generation or transmission sites.
Reply to
Charlie Siegrist

"Charlie Siegrist"

** More accurately - a 1:1 isolation tranny creates a floating AC supply by eliminating the Neutral-Ground link built into the normal AC supply.
** Completely muddled.

** Items of test equipment powered from the AC supply all have internal isolating transformers - so adding an external one makes no difference.

You seem to have mixed up the practice of " earth lifting " with the use of an isolation tranny.

....... Phil

Reply to
Phil Allison

Circa Mon, 7 May 2007 09:33:36 +1000 recorded as looks like "Phil Allison" sounds like:

Thanks for that.

Sorry for that. I wanted to keep the explanation concise, and apparently buggered the job. Suffice it to say that an IT will help prevent a person from closing a circuit with his or her body, between a hazardous voltage (wrt ground) on the hand and a ground potential at the feet. Better? I've read some of your responses about how IT's are hazardous. Do you think that the assumption that I am making about the safety advantages in a workshop environment is faulty?

All? Are you sure? I have seen oscopes give bad measurements until isolated. Perhaps the root problem was something else, and the observation was coincidental with a secondary change in test setup. I'll ponder that.

Possible. I'm a pretty mixed-up individual. Makes life interesting. Mentioning GPR, I am thinking about the isolation devices (not necessarily transformers, but more than mere gas tubes) that are permanently installed (for the purposes of isolation from remote ground) at sites where GPR is possible.

Reply to
Charlie Siegrist

"Charlie Siegrist"

** I am amazed.

** Somewhat.
** Yep.

** Yes and yes.

** You mean "ground lifted" - not " mains isolated " .

** You'll get no argument from me on that.

....... Phil

Reply to
Phil Allison

The two I've looked closely at have 2-conductor cables. These were sold in New Zealand, Australia may have different standards (or the standards may have changed since they were manufactured, but I doubt it)

Bye. Jasen

Reply to
jasen

On Sun, 06 May 2007 00:59:22 +0900, spamfree wrote: ...

Is that the American "pissed" or the Brit "pissed"? (not that there's that much difference in the effect... ;-) )

Cheers! Rich

Reply to
Rich Grise

People have been trying to get Phil to shut up for years. It's best to just ignore these tirades.

Welcome to the nut house! ;-D

Cheers! Rich

Reply to
Rich Grise

... Snipped ...

One thing I have not seen mentioned in this thread is the use of a Ground Fault Circuit Interruptor (GFCI) in situations of line-operated equipment. Operating the equipment from a GFCI outlet will offer protection against ground currents caused by touching the hot side of the line. A properly operaing GFCI will interrupt the line circuit if more than six milliamps of current is diverted to a circuit which bypasses the Neutral conductor, i.e., to a grounded piece of metal. Incidentally, the proper name for the Neutral wire is "Grounded Conductor" and the Hot wire is the "Non-Grounded Conductor".

But one should never depend on the Neutral being grounded. When outlets are daisy-chained, the possibility exists that someone has miswired the black and white wires at an outlet upstream. This is usually only a problem in equipment where the white wire has been connected to a cabinet which can be touched by the user. Double insulated tools are usually safest but if possible any serviceable equipment should be connected through a GFCI.

Ken Fowler

Reply to
Ken Fowler

"Ken Fowler"

** That's because using an *isolation tranny * defeats the operation of a GFCI.

The No 1 reason NOT to use one.

** Long as there is no * isolation tranny* in use.

** Mostly they trip at 10 or 15 mA.

** Absolute BOLLOCKS !!!

** Yep - always regard it as being live when going inside equipment.
** The Neutral inside equipment becomes LIVE and LETHAL whenever it is connected to nothing - but the Active is still connected.

A blown fuse or AC switch can create this situation any old day.

....... Phil

Reply to
Phil Allison

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