Variac question

[Ivan Vegvary]

Purchased used Variac. Good action, very smooth from 0 to 140V AC.
Question: Input and output are both 2 prong, no ground. Should I modify it to three prong with ground?
BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac? Please advise as to best procedure. Thanks. Main use of Variac will be to power up ancient tube equipment.
Thank you!

 

[John Robertson]

On 2018/11/02 9:43 PM, Ivan Vegvary wrote:

Purchased used Variac. Good action, very smooth from 0 to 140V AC.
Question: Input and output are both 2 prong, no ground. Should I modify it to three prong with ground?
BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac? Please advise as to best procedure. Thanks. Main use of Variac will be to power up ancient tube equipment.
Thank you!

As long as the variac passes basic eletrical leakage test fine and the
powre cord and internal wiring are in good condition there is little
sense in trying to upgrade it to three conductor wiring.

In fact I recall reading somewhere (can't find the link) that it is
against the electrical safety regulations to convert two conductor
products to three conductor. This could be incorrect, until I can find
the reference take it with a grain of salt. However many items wired for
two conductor would need to be modified for three conductor beyond just
adding a ground - in pinball and jukeboxes the older two conductor items
correctly had the power switch on one side of the line and the line fuse
on the other - this is totally wrong on three wire setups!

So use the isolation Xformer to be safe.

Also, I trust you are aware of the series lamp (25 to 100W bulb
depending on the load) test for powering up gear that you aren't sure
hasn't a problem (shorted winding, cap, rectifier, etc.)...

John :-#)#
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[Phil Allison]

Ivan Vegvary wrote:

Purchased used Variac. Good action, very smooth from 0 to 140V AC.

Question: Input and output are both 2 prong, no ground.
Should I modify it to three prong with ground?

** Yes - all modern ones are made like that. It is not safe to de-earth an appliance just because you need to use a Variac with it.

BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac?
Please advise as to best procedure.

** Either way works, feeding 140VAC to the Iso may get it a bit hot though.

Main use of Variac will be to power up ancient tube equipment.

** I use mine for almost everything.

Cos I hate blowing fuses at switch-on.


..... Phil

 

[Phil Allison]

John Robertson wrote:

As long as the variac passes basic eletrical leakage test fine and the
powre cord and internal wiring are in good condition there is little
sense in trying to upgrade it to three conductor wiring.

** To maintain the safety of equipment that normally uses a ground conductor with a 3 pin plug - earth continuity must remain intact.

In fact I recall reading somewhere (can't find the link) that it is
against the electrical safety regulations to convert two conductor
products to three conductor.

** If the product as originally sold was of Double Insulated (aka class2) design, this may be true. Earthing a Class 2 shaver is silly.

But I would not hesitate to add a 3 conductor cable to any guitar amp, powered desk or similar I found that did not have it.

This could be incorrect, until I can find
the reference take it with a grain of salt. However many items wired for
two conductor would need to be modified for three conductor beyond just
adding a ground - in pinball and jukeboxes the older two conductor items
correctly had the power switch on one side of the line and the line fuse
on the other - this is totally wrong on three wire setups!

** Sounds easy enough to correct, as it is to remove the infamous "death cap" fitted to many 2 wire guitar amps not so long ago.



..... Phil

 

On Saturday, 3 November 2018 04:43:21 UTC, Ivan Vegvary wrote:

Purchased used Variac. Good action, very smooth from 0 to 140V AC.
Question: Input and output are both 2 prong, no ground. Should I modify it to three prong with ground?

it's safer to

BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac? Please advise as to best procedure. Thanks. Main use of Variac will be to power up ancient tube equipment.
Thank you!

that works, but don't assume you won't then get a shock from a live wire. Safer & easier now to use an RCD/GFCI.


NT

 

[Cursitor Doom]

On Fri, 02 Nov 2018 21:43:18 -0700, Ivan Vegvary wrote:

Purchased used Variac. Good action, very smooth from 0 to 140V AC.
Question: Input and output are both 2 prong, no ground. Should I modify
it to three prong with ground?

I certainly would.

BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac? Please
advise as to best procedure. Thanks. Main use of Variac will be to
power up ancient tube equipment.
Thank you!

The isolation transformer should always power the *device under test* to
remove the Earth reference from it.




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[Ralph Mowery]

In article <X-WdneIGd9CSrUDGnZ2dnUU7-XHNnZ2d@giganews.com>,
spam@flippers.com says...

In fact I recall reading somewhere (can't find the link) that it is
against the electrical safety regulations to convert two conductor
products to three conductor. This could be incorrect, until I can find
the reference take it with a grain of salt. However many items wired for
two conductor would need to be modified for three conductor beyond just
adding a ground - in pinball and jukeboxes the older two conductor items
correctly had the power switch on one side of the line and the line fuse
on the other - this is totally wrong on three wire setups!

In just the last few years I have been looking at the older equipment (
some in the mid 1960s) and they were 2 wire devices. They had the
switch on one side of the transformer and the fuse on the other side. I
don't know about the code or why it was done that way. I would have
thought the fuse would come first on the hot wire and then the switch.
Much of the equipment is ham radio related and most users would have a
good connection of the chassis to the earth ground.

 

[Fox's Mercantile]

On 11/3/18 9:37 AM, Ralph Mowery wrote:

In just the last few years I have been looking at the older equipment
(some in the mid 1960s) and they were 2 wire devices. They had the
switch on one side of the transformer and the fuse on the other side.
I don't know about the code or why it was done that way. I would have
thought the fuse would come first on the hot wire and then the switch.
Much of the equipment is ham radio related and most users would have a
good connection of the chassis to the earth ground.

Because in the end, it's a series circuit. It doesn't make a damn bit of
difference.

Primarily, it was done from a "Is this the cheapest and easyist (also
cheapest) way to do it this way?"




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http:foxsmercantile.com

 

[Ivan Vegvary]

Thank you everybody. Great help! Will always use the isolation xformer

 

[Cursitor Doom]

On Sat, 03 Nov 2018 10:38:54 -0700, Ivan Vegvary wrote:

> Thank you everybody. Great help! Will always use the isolation xformer

One last thing: don't ever get into the habit of using that variac of
yours as a convenient substitute for an extension lead.
Enjoy!




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On Saturday, 3 November 2018 15:05:48 UTC, Fox's Mercantile wrote:

On 11/3/18 9:37 AM, Ralph Mowery wrote:

In just the last few years I have been looking at the older equipment
(some in the mid 1960s) and they were 2 wire devices. They had the
switch on one side of the transformer and the fuse on the other side.
I don't know about the code or why it was done that way. I would have
thought the fuse would come first on the hot wire and then the switch.
Much of the equipment is ham radio related and most users would have a
good connection of the chassis to the earth ground.

Because in the end, it's a series circuit. It doesn't make a damn bit of
difference.

Primarily, it was done from a "Is this the cheapest and easyist (also
cheapest) way to do it this way?"

It makes a huge difference.
Fuse in live blown: faulty equipment is now dead.
Fuse in neutral blown: faulty equipment looks dead but is live.
One can electrocute you after a live to case fault, the other won't.
This is why UK banned dual pole mains fusing in 1955.


NT

 

[Phil Allison]

Ivan Vegvary wrote:

Thank you everybody.
Great help! Will always use the isolation xformer

** Who here said to do that ???

Good safety practice is to use an isolation ONLY when you need to - as with old live chassis radios or off-line SMPUs.

Never disconnect your scope from safety earth and if equipment on test has the safety ground connected to the chassis - leave it that way.



..... Phil

 

[Ralph Mowery]

In article <839ff2eb-6ef5-4f76-aae9-18bf09ede457@googlegroups.com>,
tabbypurr@gmail.com says...

It makes a huge difference.
Fuse in live blown: faulty equipment is now dead.
Fuse in neutral blown: faulty equipment looks dead but is live.
One can electrocute you after a live to case fault, the other won't.
This is why UK banned dual pole mains fusing in 1955.

Ideas and codes change from one country to the next and sometimes even
in the same country.

In my opinion one of the worst things was some equipment where aI
worked. The standard in the US was that on electrical equipment boxes
red was off and green was on. We got in some equipment from Europe and
they used Green for off and Red for on. The reason being that Green was
safe to open the door and red ment power was on and danger.


I know that in a series circuit that electrically it does not matter in
which order things are for them to work. I was just courious that much
of the older two wire 120 volt stuff that has a transformer , the power
comes in, then a switch, transformer primary , fuse and back out to the
power. I would have thought it would be the power, fuse, switch,
transformer and back out to power.

 

On Sunday, 4 November 2018 03:58:17 UTC, Ralph Mowery wrote:

In article <839ff2eb-6ef5-4f76-aae9-18bf09ede457@googlegroups.com>,
tabbypurr says...

It makes a huge difference.
Fuse in live blown: faulty equipment is now dead.
Fuse in neutral blown: faulty equipment looks dead but is live.
One can electrocute you after a live to case fault, the other won't.
This is why UK banned dual pole mains fusing in 1955.




Ideas and codes change from one country to the next and sometimes even
in the same country.

In my opinion one of the worst things was some equipment where aI
worked. The standard in the US was that on electrical equipment boxes
red was off and green was on. We got in some equipment from Europe and
they used Green for off and Red for on. The reason being that Green was
safe to open the door and red ment power was on and danger.


I know that in a series circuit that electrically it does not matter in
which order things are for them to work. I was just courious that much
of the older two wire 120 volt stuff that has a transformer , the power
comes in, then a switch, transformer primary , fuse and back out to the
power. I would have thought it would be the power, fuse, switch,
transformer and back out to power.

The only justification I can think of for the old practice of putting the switch & fuse in different leads for unpolarised kit is the idea that the switch is a relative weakpoint, so would likely act as a higher current fuse if there were a short from live to some good earth - not good but better than nothing. I suppose it's also marginally easier for production to have 2 things to solder the mains wires to.


NT

 

[Cursitor Doom]

On Sat, 03 Nov 2018 23:58:08 -0400, Ralph Mowery wrote:

In my opinion one of the worst things was some equipment where aI
worked. The standard in the US was that on electrical equipment boxes
red was off and green was on. We got in some equipment from Europe and
they used Green for off and Red for on. The reason being that Green was
safe to open the door and red ment power was on and danger.

And just to further complicate matters, in domestic consumer units
nowadays, the spur is live when the switch is in the 'up' position and
'off' is down. This is arse-about-face to what I - at least - was brought
up with in the UK.




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[Ralph Mowery]

In article <prmice$bk8$3@dont-email.me>, curd@notformail.com says...

And just to further complicate matters, in domestic consumer units
nowadays, the spur is live when the switch is in the 'up' position and
'off' is down. This is arse-about-face to what I - at least - was brought
up with in the UK.

I live in the US. I don't know if it the code or not, but just about
all the light switches and many other types that work up and down, the
up is on and the down is off.

From what I have heard in the UK up is off and down is on for house
light switches.

I only have a couple of things around the house that have vertical
switches. The ones from China are up for on, but one from Japan is down
for on. Most everything else is push button and that is push in for on
if the switch stays in. On some the pushbutton just returns to the out
position.

 

[Mike Coon]

In article <MPG.3648dff866abc29f9898df@news.east.earthlink.net>,
rmowery28146@earthlink.net says...

From what I have heard in the UK up is off and down is on for house
light switches.

Yes, power outlets too; pretty general default. But I was aware (having
visited several times) that USA was opposite. Maybe something to do with
driving on left or right?

Mike.

 

[Roger Blake]

On 2018-11-04, Ralph Mowery <rmowery28146@earthlink.net> wrote:

From what I have heard in the UK up is off and down is on for house
light switches.

What else would you expect from people who inist upon driving on the
wrong side of the road? (At least the Swedes wised up in the 1960s.)

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[gregz]

Ivan Vegvary <ivanvegvary@gmail.com> wrote:

Purchased used Variac. Good action, very smooth from 0 to 140V AC.
Question: Input and output are both 2 prong, no ground. Should I modify
it to three prong with ground?
BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac? Please
advise as to best procedure. Thanks. Main use of Variac will be to power
up ancient tube equipment.
Thank you!

I would place ISO XFMR after variac. The transformer is not 1:1 and
designed to be 1:1 under full load. Depends on current either way you can
end up say 160 volts no load.

Greg

 

[gregz]

Ivan Vegvary <ivanvegvary@gmail.com> wrote:

Purchased used Variac. Good action, very smooth from 0 to 140V AC.
Question: Input and output are both 2 prong, no ground. Should I modify
it to three prong with ground?
BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac? Please
advise as to best procedure. Thanks. Main use of Variac will be to power
up ancient tube equipment.
Thank you!

There are different types of isolation transformers. The ones many sell in
US with outlets and all, have three prong grounded outlets, and that groung
is tied to one leg of output forming new neutral. These are specific for
reducing noise. No ground isolation.

Greg