Variac question

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

** 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

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

** I use mine for almost everything.

Cos I hate blowing fuses at switch-on.

.... Phil

it's safer to

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

I certainly would.

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

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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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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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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

** 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

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 s witch & fuse in different leads for unpolarised kit is the idea that the sw itch 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 th an nothing. I suppose it's also marginally easier for production to have 2 things to solder the mains wires to.

NT

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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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.

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.

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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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

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