isolation transformer needed

[David Nebenzahl]

On 12/30/2009 2:26 PM Phil Allison spake thus:

[snip abuse]

Phil: Take your fucking meds and SHUT UP!!!!!


--
I am a Canadian who was born and raised in The Netherlands. I live on
Planet Earth on a spot of land called Canada. We have noisy neighbours.

- harvested from Usenet

 

[Phil Allison]

"Dave Plowman = Lying Pile of SHIT "

I've got no objection to anyone saying I'm wrong.

** You ALWAYS 100% WRONG !!!

And you HATE being told SOOOO much you ALWAYS attack the messenger.

Provided they back it up with facts.

** Problem being - YOU are such a TOTAL FUCKWIT

you have clue what the relevant facts are !!

You dismiss them every time as irrelevant and post DRIVEL instead.

Mains electricity is always dangerous. Using an isolation
transformer can *reduce* that hazard. Not *eliminate* it.

** It actually increases it in the service bench situation.

For reason that are forever incomprehensible to FUCKWITS like YOU !!

And as regards
connecting a grounded mains 'scope probe etc to equipment under repair
which you've fed via an isolating transformer - words fail me.

** In most case, the only reason for using a mains isolation tranny

is JUST SO YOU CAN DO THAT !!!!!!!

You fucking IGNORANT pommy TWAT !!

How the fuck do you imagine folk fix off-line SMPS ???
----------------------------------------------------------------

You have ZERO electronics knowledge.

FUCK OFF AND DIE !!



.... Phil

 

[Phil Allison]

"David Nebenzahl"


** Scumbags like YOU need a bullet in the head.




..... Phil

 

[Dave Plowman (News)]

In article <hhga7b$mct$1@speranza.aioe.org>,
D Yuniskis <not.going.to.be@seen.com> wrote:

Hi Dave,

Dave Plowman (News) wrote:
See our Oz retard is at it again...

Hmmm... was this the Phil guy? I didn't see the post to
which you are replying -- and he is the only entry in my
killfile, here (though it could just be the original post
hasn't made it to my server).

I ask only because my filter was *supposed* to kill the
entire thread and not just his post (i.e., I shouldn't
have seen your followup to his post -- if indeed that
was the case).

--don

Yes - it was Phil Allison. I don't killfile anyone as it's just as easy to
ignore a post. What is so sad about Phil is he often posts useful
information. But also pollutes Usenet worldwide with his potty mouth.

--
*Never kick a cow pat on a hot day *

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Dave Plowman (News)]

In article <3dcg89.io8.17.11@news.alt.net>,
Meat Plow <meat@petitmorte.net> wrote:

On Wed, 30 Dec 2009 22:23:51 +1100, "Phil Allison"
phil_a@tpg.com.au>wrote:

.... Phil

Yes you do give very bad advice.

I've got no objection to anyone saying I'm wrong. Provided they back it up
with facts. Mains electricity is always dangerous. Using an isolation
transformer can *reduce* that hazard. Not *eliminate* it. And as regards
connecting a grounded mains 'scope probe etc to equipment under repair
which you've fed via an isolating transformer - words fail me. Someone
that thick that they don't understand the safety issues should stick to
playing with themselves - like Phil.

--
*Dancing is a perpendicular expression of a horizontal desire *

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[sparky]

On Dec 30, 8:20 pm, "Dave Plowman (News)" <d...@davenoise.co.uk>
wrote:

In article <3dcg89.io8.17...@news.alt.net>,
   Meat Plow <m...@petitmorte.net> wrote:

On Wed, 30 Dec 2009 22:23:51 +1100, "Phil Allison"
phi...@tpg.com.au>wrote:
....   Phil
Yes you do give very bad advice.

I've got no objection to anyone saying I'm wrong. Provided they back it up
with facts. Mains electricity is always dangerous. Using an isolation
transformer can *reduce* that hazard. Not *eliminate* it. And as regards
connecting a grounded mains 'scope probe etc to equipment under repair
which you've fed via an isolating transformer - words fail me. Someone
that thick that they don't understand the safety issues should stick to
playing with themselves - like Phil.

Dave, You seem to loack a basic understanding of isolation
transformers
and service techniques. The isolation transformer allows you to
scope
probe at any part of the circuit and create a "virtual ground"
anywhere in
the circuit.
Isolation transformers do not eliminate shock hazard but are a
very usefull
tool on the service bench. If used by someone with the KNOWLEDGE
to use it.
..
..

 

[Dave Plowman (News)]

In article
<9379d4f2-0894-4d69-b253-ceec49ff6fae@c3g2000yqd.googlegroups.com>,
sparky <sparky12x@yahoo.com> wrote:

I've got no objection to anyone saying I'm wrong. Provided they back
it up with facts. Mains electricity is always dangerous. Using an
isolation transformer can *reduce* that hazard. Not *eliminate* it.
And as regards connecting a grounded mains 'scope probe etc to
equipment under repair which you've fed via an isolating transformer -
words fail me. Someone that thick that they don't understand the
safety issues should stick to playing with themselves - like Phil.

Dave, You seem to loack a basic understanding of isolation
transformers and service techniques. The isolation transformer allows
you to scope probe at any part of the circuit and create a "virtual
ground" anywhere in the circuit. Isolation transformers do not eliminate
shock hazard but are a very usefull tool on the service bench. If
used by someone with the KNOWLEDGE to use it. .

There is no reason to have the 'ground' on your scope connected to actual
ground - with a suitable 'scope. Or perhaps you ground one leg of your DVM?

You seem to lack basic understanding of safe working practices.

--
*Do paediatricians play miniature golf on Wednesdays?

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[sparky]

You seem to lack basic understanding of safe working practices.

Have you ever worked on a piece of equipment ?

Certainly not effectively !

Certainly not safely !

 

[Dave Plowman (News)]

In article
<0b678d42-1c0e-4a0e-97a6-4dac22decfac@s3g2000yqs.googlegroups.com>,
sparky <sparky12x@yahoo.com> wrote:

You seem to lack basic understanding of safe working practices.

Have you ever worked on a piece of equipment ?

Of course.

Certainly not effectively !

Really?

Certainly not safely !

Perhaps you could give the reasons why things *must* be grounded under all
circumstances. If you actually understand the dangers of this, of course.

--
*If at first you do succeed, try not to look too astonished.

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[D Yuniskis]

Dave Plowman (News) wrote:

In article <hhga7b$mct$1@speranza.aioe.org>,
D Yuniskis <not.going.to.be@seen.com> wrote:
Hi Dave,

Dave Plowman (News) wrote:
See our Oz retard is at it again...

Hmmm... was this the Phil guy? I didn't see the post to
which you are replying -- and he is the only entry in my
killfile, here (though it could just be the original post
hasn't made it to my server).

I ask only because my filter was *supposed* to kill the
entire thread and not just his post (i.e., I shouldn't
have seen your followup to his post -- if indeed that
was the case).

Yes - it was Phil Allison. I don't killfile anyone as it's just as easy to

Understandable. I spend so little time on USENET that I prefer
if my newsreader does *some* of my work for me :>

ignore a post. What is so sad about Phil is he often posts useful
information. But also pollutes Usenet worldwide with his potty mouth.

<frown> I will have to explore why my filter didn't mark
the entire thread. :<

 

[mike]

Dave Plowman (News) wrote:

In article
0b678d42-1c0e-4a0e-97a6-4dac22decfac@s3g2000yqs.googlegroups.com>,
sparky <sparky12x@yahoo.com> wrote:

You seem to lack basic understanding of safe working practices.

Have you ever worked on a piece of equipment ?

Of course.

Certainly not effectively !

Really?

Certainly not safely !

Perhaps you could give the reasons why things *must* be grounded under all
circumstances. If you actually understand the dangers of this, of course.

"Ground" is a concept.

It's convention; that is we agree on the definition.
(I know, agreement is a foreign concept to you...just go with it.)
We drive a metal stake in the earth and call it ground.
If you don't put any current in the stake, you can use it
as a reference for all measurements. If you need a differential
measurement, just measure the two relative to "ground" and subtract.
Works just fine in concept.

As a practical matter, it takes much less "technology" to make a local
single-ended measurement relative to a "common" point. That
common point is often pretty close to "ground"...doesn't have to be,
it's just easier to work with and easier to make safe.

This paradigm creates systems that are "safe" in most cases, when they're
working properly and are still safe under the most common fault conditions
as long as you leave the covers on the system. When you open the box,
many safety assumptions don't apply.


There are exceptions, but when you use an isolation transformer to
"disconnect" the local common from the conceptual "ground", you don't
necessarily make a properly functioning system any less "safe" under
normal operation.

An Isolation Transformer is not inherently unsafe.
But an isolation transformer does NOT make a faulty system SAFE to poke
around inside.

What IS unsafe is the stupid things people do with their hands and test
equipment
believing that the transformer absolves them from any responsibility to
THINK about
what they're doing. Redefining your own
common reference by attaching an arbitrary node inside the faulty supply to
your local concept of "ground" is decidedly UnSAFE.

While I'm on the subject of RESPONSIBILITY...
People ask questions because the don't know the answer. In many cases,
they can't
even tell if the advice they're getting is good or bad. One way is to
vote.
If two, or three or four people said it, it must be true. Problem is
that the most vocal newsgroup
denizens are demonstrating the least ability to think about and
understand the consequences of their
advice. And there are WAY more than two people giving bad advice here.

One way to judge advice is the tone of the thread. Name-calling is what
you do when you
don't have a logical leg to stand on. A spirited, yet civil, debate
often leads to consensus.
That advice is more likely to be helpful.
As soon as the name-calling starts, you can't trust any advice from the
thread. Some of the input may be helpful, but you can't tell which,
or you wouldn't have had to ask the question in the first place.

We have the responsibility to do no harm, and argue logically against
unsafe advice.

Doing stupid, unsafe things may work 99% of the time. As long as that 100th
time is YOU, I don't have a problem with the odds...I'd buy a ticket to
watch.
If that 100th time is some
innocent guy who took your bad advice, I have a BIG problem.

 

[Phil Allison]

"mike"

Normally, I'd not waste my time trying to train
internet denizens.

** Or teaching pigs to sing.

The primary reason to want an isolation transformer to
troubleshoot a power supply is to work on the primary side.
Now, the KEY word is TROUBLESHOOT. What that means is that
the power supply has a FAULT in the primary circuit.
What's the fault? You don't know, or you'd just fix it.
How safe is it to troubleshoot that particular fault?
You don't know, 'cause you don't know what it is.

You're gonna RISK ELECTROCUTION based on the misguided
assumption that an isolation transformer keeps you safe.
YOU'RE NOT SAFE. YOU DON'T HAVE ANY IDEA WHAT THE PRIMARY
CIRCUIT IS, BECAUSE IT'S NOT AS DESIGNED. IT HAS A FAULT!!!!!!!
The node that the designer called common may not be common
at all. IT HAS A FAULT!!!! You should not arbitrarily ground
ANY node. It has a fault!!! (I'm skipping over the obvious
question, "what is ground anyway?")

An isolation transformer is not inherently bad. It can
provide a layer of protection. What is bad is the FALSE
sense of security
that the transformer makes it safe to poke around inside
a supply WITH A PRIMARY FAULT.

** Standard procedure for servicing any unit with an unknown fault is to
FIRST see what happens when plugged into a normal AC outlet - ie one with
neutral and ground linked at the service box.

That outlet MUST have an RCD fitted as a standard safety precaution for
ANYONE working on mains powered equipment while it is energised.

The RCD will trip if the unit has a fault that causes even 10mA of leakage
from the AC supply to ground - which includes a short from internal
neutral conductors to safety ground.

If the unit is of class 2 ( double insulated ) construction, the external
metalwork should be linked to safety ground in order to test the integrity
of that insulation and render the unit safe to handle.

Obviously, if the RCD trips under these initial tests the cause MUST be
tracked down and dealt with before going any further.

The ONLY time a service tech needs to use a mains isolation transformer is
when the unit has a "live chassis" as some TV sets do OR it contains an
off-line SMPS that needs detailed analysis with a scope in order to effect
repairs.

The tech must be VERY aware that the electric shock protection afforded by
the RCD is LOST when the isolation tranny is in use and so use it as
sparingly as possible. It a damn good idea to have the isolation tranny
VERY visible on the bench to constantly remind the tech it is in use.

When work is completed, the unit should be again connected to a normal, RCD
protected, outlet and checked.

If the unit it uses class 2 insulation, the AC leakage current to safety
ground should be measured with a suitable load and meter. The leakage
current should not exceed 0.5 to 1 mA, depending on the item and the actual
AC voltage in use.

There are a host of other checks and inspections a service tech needs to do
on and around the AC wiring, fusing devices and any AC power leads and plugs
attached to a unit. Any parts that are damaged, worn out or otherwise seem
unsafe must be repaired or replaced.

I go through a LOT of AC plugs, fuses and fuse holders in my work.



...... Phil

 

[Jeff Liebermann]

On Wed, 30 Dec 2009 00:23:40 +0000 (GMT), "Dave Plowman (News)"
<dave@davenoise.co.uk> wrote:

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely. That plus an RCD feeding it provides the best degree of safety
in the workshop. I'm surprised you don't see this.

What's an RCD? We call it an GFCI on the other side of the pond:
<http://en.wikipedia.org/wiki/Residual-current_device>

If you put a transformer before or after the GFCI, any leakage current
between either side of the xformer secondary will have no path to
ground. The GFCI won't trip.

You can prove it to yourself. Find a GFCI. Plug in a common 5, 9,
12, or whatever AC output wall wart into the GFCI. Touch one of the
output pins (xformer secondary) to the AC ground somewhere. The GFCI
won't trip. Neither will a faulty power supply, sitting on the output
of the isolation transformer.

I found this out the hard way. At the advice of a former friend, I
built a test box consisting of a variac, isolation transformer,
circuit breakers, voltmeter, ammeter, and GFCI. A power cord line
input and several wall jacks for the outputs. After getting zapped,
shocked, and fried several times without the GFCI ever tripping, I
realized that this wasn't going to work. The only real advantage to
this derrangement was that I could use my grounded oscilloscope
without fear of destroying the scope probe lead.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

 

[Dave Plowman (News)]

In article <hhjcm2$57a$1@news.eternal-september.org>,
mike <spamme0@go.com> wrote:

Perhaps you could give the reasons why things *must* be grounded under
all circumstances. If you actually understand the dangers of this, of
course.

"Ground" is a concept.
It's convention; that is we agree on the definition.
(I know, agreement is a foreign concept to you...just go with it.)

It certainly is since in the UK we call a mains ground earth.

We drive a metal stake in the earth and call it ground.
If you don't put any current in the stake, you can use it
as a reference for all measurements. If you need a differential
measurement, just measure the two relative to "ground" and subtract.
Works just fine in concept.

Really? You seem to have strange ideas about what is a reverence.

As a practical matter, it takes much less "technology" to make a local
single-ended measurement relative to a "common" point. That
common point is often pretty close to "ground"...doesn't have to be,
it's just easier to work with and easier to make safe.

So qualify just how you do this in the workshop.

This paradigm creates systems that are "safe" in most cases, when
they're working properly and are still safe under the most common fault
conditions as long as you leave the covers on the system. When you open
the box, many safety assumptions don't apply.

There are certain rules that apply.

There are exceptions, but when you use an isolation transformer to
"disconnect" the local common from the conceptual "ground", you don't
necessarily make a properly functioning system any less "safe" under
normal operation.

Sigh. I'm utterly amazed you can't see how having both legs of a dangerous
voltage floating is safer than having one side of it grounded.

An Isolation Transformer is not inherently unsafe.
But an isolation transformer does NOT make a faulty system SAFE to poke
around inside.

Who said it did? Nothing can make dangerous voltages safe for idiots.

What IS unsafe is the stupid things people do with their hands and test
equipment believing that the transformer absolves them from any
responsibility to THINK about what they're doing. Redefining your own
common reference by attaching an arbitrary node inside the faulty supply
to your local concept of "ground" is decidedly UnSAFE.

Darwin's rule applies, then. Anyone who doesn't understand potential
difference is best suited to having knitting as a hobby.

--
*The hardness of the butter is proportional to the softness of the bread *

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[David]

In article <50d1cb4d98dave@davenoise.co.uk>,
"Dave Plowman (News)" <dave@davenoise.co.uk> wrote:

In article <hhfd8h$jdr$1@news-01.bur.connect.com.au>,
Phil Allison <phil_a@tpg.com.au> wrote:
"Dave Plowman Ignorant Fucking Nutcase"


The notion he describes is 100% FALSE and totally discredited
many decades ago as a very DANGEROUS practice.

No it hasn't. Isolation transformers are still used for many safety
related reasons. But don't expect you to understand why. Obviously.

I am one of those who rarely agree with Phil, but this time he is giving
you the right info.

From your post Dave it does seem you do not understand the reasons
behind the use of isolation xformers when working on or testing gear.

No matter how much you appear to dislike Phil, there are times when it
pays to bow to other's areas of expertise - and while Phil is hopeless
with people skills, he does know electronics/electrical equipment

David

 

[William Sommerwerck]

Thank you for posting this. It answered several questions I've had for a
long time.

Read this document carefully, as it is something you will rarely
encounter -- a technical document written by someone who actually knows how
to write!

Will wonders never cease?

 

[Leonard Caillouet]

Please see page 2.

http://www.cbtricks.com/miscellaneous/tech_publications/scope/floating.pdf

 

[Meat Plow]

On Fri, 1 Jan 2010 12:22:41 +1100, "Phil Allison"
<phil_a@tpg.com.au>wrote:

** Standard procedure for servicing any unit with an unknown fault is to
FIRST see what happens when plugged into a normal AC outlet - ie one with
neutral and ground linked at the service box.

Funny that was never on any service literature or diagnostic procedure
documentation I ever read. Nor would I have ever made it my own
practice as a first step thinking back 30 through 30 years.

But then again this is an internationally mirrored forum so I don't
really try to pawn off my particular service procedures as the gospel
where the diagnostics flow chart may be much different in certain
regions of the globe.

HAND

 

[Phil Allison]

"Meat Head Moron "

"Phil Allison"


** Standard procedure for servicing any unit with an unknown fault is to
FIRST see what happens when plugged into a normal AC outlet - ie one
with
neutral and ground linked at the service box.

Funny that was never on any service literature or diagnostic procedure
documentation I ever read. Nor would I have ever made it my own
practice as a first step thinking back 30 through 30 years.

** My post does NOT say that it is the very first step.

It does say that with an unknown but possible PSU fault - connection to a
normal RCD protected AC outlet should be done FIRST - before using an
isolation tranny.

Obviously, visual inspection comes very first, including carefully checking
of the AC plug, lead and fuse if accessible. If the AC fuse is missing or
blown, then a major fault is likely.

In the latter case, MY procedure is to install a suitable new AC fuse and
gradually bring up the item using a variac - all the time monitoring the
current draw from the AC supply with meter specially built for that purpose.
If the AC current becomes unusually large ( or the RCD trips) as the AC
voltage rises - game over.



..... Phil

 

[Dave Plowman (News)]

In article <postings-27DDC5.17183701012010@news.bigpond.com>,
David <postings@REMOVE-TO-REPLYconfidential-counselling.com> wrote:

No it hasn't. Isolation transformers are still used for many safety
related reasons. But don't expect you to understand why. Obviously.

I am one of those who rarely agree with Phil, but this time he is giving
you the right info.

From your post Dave it does seem you do not understand the reasons
behind the use of isolation xformers when working on or testing gear.

Seems to me some expect the use of an isolation transformer to be some
form of magic bullet that removes all risks. It doesn't. But can reduce
the sort of risk caused by one side of a mains supply being grounded. If
you then ground one leg of the output of that transformer by any means you
are back to square one.
However, I can't think of any case where the use of an isolation
transformer *increases* any hazard.

--
*The early bird gets the worm, but the second mouse gets the cheese *

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.