Electric shocks (was: 100V appliance on 110v power supply)

When I said "I've got a Japanese Akai S1000 sampler", I actually meant "I'm selling a Japanese Akai S1000 sampler for someone else". As a result, I didn't know much about the unit and its condition.

But I asked the owner what she used to do with regards to power supply and she gave me the transformer that she had been running it off for the past 7 years or so. Surprise surprise - it's a 240V to 115V transformer, and she said the Akai always worked fine despite being labelled 100V. In other words, she'd been using an incorrect transformer for years, but it worked anyway.

A buyer emailed me today from eBay asking if the screen was still bright or if it had gone dim with age, so I plugged in the sampler using aforementioned 115V transformer and promptly got an electric shock from an area on the sampler's case where a bit of the paint had been scratched off, leaving bare metal. It is worth bearing in mind that I was barefoot and standing on a concrete garage floor, but nevertheless, this shouldn't happen. I plugged it in again and the same thing happened. However, when turned on, the sampler worked fine - it just gave me a shock whenever I touched the case (a sizeable electric shock, not like static). The owner said that she'd never experienced this before despite using the sampler with the same transformer on a UK mains supply.

One thing I noticed about the unit was that it used a 2-pin power lead with apparently no earth. As in, the socket on the machine only had 2 pins, so there was no option to use an earthed cable (even though the transformer had earthed sockets). What's the deal with this? Can anything be done? Obviously I can't sell a unit on eBay in Very Good Condition if it shocks you when you plug it in, even if it works fine otherwise.

Is my only option to sell it as-seen with a buyer warning?

Thanks,

-- tj hertz

Reply to
TJ Hertz
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Generously-designed equipment can likely take a 15% over- voltage although it may run warmer (and may reduce its expected lifespan.) But lots of modern equipment is designed on the very edge of acceptable ranges, so I wouldn't try it as a rule.

PLEASE DON'T do that experiment again. We would miss you if you electrocuted yourself! Seriously! There are SAFE ways of testing for this that don't put your life or limb at risk.

Now that you know about it, and especially now that you have revealed it in public, you really have no ethical choice but to disclose it to any potential buyer. If somebody bought it and electrocuted themselves full disclosure would be your minimum defense.

If it were me, I would be tempted to fit an IEC power connector on it (like the kind used for computers), with the green-wire ground securely bonded to the metal chassis. But mains wiring is not a project for amateurs. I would think that most consumer equipment service shops ("TV Repair", etc.) would be equipped for and experienced with testing and fixing this kind of problem.

Ironically, it may be working just as it was designed back when it was first sold. But you can't get away without telling bidders about the hazard today IMHO.

Reply to
Richard Crowley

If you sell this product, even with a warning, you are opening up yourself to servere liability issues.

An electric shock can be painful under the best conditions and potentially deadly under the worst conditons.

It's likely that the transformer that the person you bought this from was providing isolation and hence their claim of no shocks may have valid.

Beachcomber

Reply to
Beachcomber

Someone pointed out the online manual. It has specific mention of earthing in certain regions. You might want to take a look. Maybe something there will be worth knowing.

j
Reply to
operator jay

Yeah, I know, and that's probably what I'll do - I was just asking if there were any ways of fixing it. Obviously if the problem remains I will warn any buyer.

I'll take it into a repair shop methinks. Thanks for the help.

TJ

-- tj hertz

Reply to
TJ Hertz

It appears that the original usage was 240V to ground and the transformer is an autotransformer. Using this transformer with a North American 240/120V system could put the case at 120V with respect to ground. If this unit is to be used with a transformer, it will require an isolating (2 winding) 240/120V transformer and then the case can be grounded.

However, why use the transformer?

Why not connect directly to the 120V outlet. It will be necessary to determine which lead is the neutral. You will need a voltmeter. If the case is at 120 or so Volts to ground- reverse the wires to the plug. Check again-you want a small or negligable voltage between case and ground. Then set up the plug and leads accordingly (replacing the cord and plug to a 3 prong (hot, neutral and ground) is the best way. If you have any doubts, a competent electrician can sort it out for you in a short time- or you warn the potential buyer that it appears that the case is tied to the neutral and you don't know which wire is neutral and leave the correction to him/her. You don't want to be responsible for avoidable injuries.

Reply to
Don Kelly

So basically, you're saying find out which way the thing should be connected in order to let the case be neutral, replace the mains end of the cable with a 3-pin plug so that it can't be connected the wrong way, and glue/fix the sampler end of the cable into the sampler so it can't be reversed (or label which way it should go)? And this would fix the electric shock problem, but still leave the unit unearthed?

I'll let an electrician deal with it because I have neither a volt/multimeter nor any spare 3-pin plugs (you don't see many in the UK), but I'd like to know what's going on anyway.

Thanks

-- tj hertz

Reply to
TJ Hertz

Are those common in England? I've never seen any.

Reply to
Richard Crowley

On the shaving mirror in hotels . I just would not plug good electronics into it :O

, _ , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw snipped-for-privacy@JUNKmindspring.com , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped?

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Reply to
Steve Urbach

Should be no problem, except they are limited to 25W with a slow acting thermal cutout. The output is isolated via an isolating transformer (floating).

Reply to
Andrew Gabriel

Reply to
w_tom

"w_tom"

** Making it no longer an "isolation " transformer.
** The appliance's AC supply wiring will float - but nothing else since it is all insulated from that wiring.
** A step-down / isolation transformer ought to have a ground terminal on the outlet that connects to the METALWORK of the appliance via the third pin of the plug.

.......... Phil

Reply to
Phil Allison

From: snipped-for-privacy@tpg.com.au (Phil=A0Allison) "w_tom" =A0=A0Ioslation transformer must still have the secondary (the 120 volt side) connected back to the building safety ground.

** Making it no longer an "isolation " transformer. If not, then the appliance will 'float' - can become electrically hot. ** The appliance's AC supply wiring will float - but nothing else since it is all insulated from that wiring. If the transformer is properly designed, then either it has such a connection OR it has a dedicated grounding wire terminal to make that necessary connection. ** A step-down / isolation transformer ought to have a ground terminal on the outlet that connects to the METALWORK of the appliance via the third pin of the plug. ......... =A0 Phil

All those observations seem all for naught to me, since he as a Hot Chassis Item. It behooves whom ever get's to keep it to isolate the works 100% from that chassis with plastic or insulated offsets to avoid any objectionable current flowing through it as he's experienced., Or keep it as is and Fancy Oneself in those days.

Point: No Manner of Transformer will correct the condition & a seperate ground conductor will only disguise the fault.

He should have plugged it in his safe insulated floored section, but then again it was all for the better :-)

=AEoy

Reply to
Roy Q.T.

No, that's the point of isolation. Because the appliance floats, it can become "hot" but the leakage current has no reference to the building ground so if you touch the hot case, no current will flow through you.

Not that a safety ground isn't _still_ a good idea, mind you.

--scott

Reply to
Scott Dorsey

Yes, that's why in all around the world the neutral of LV distribution transformers is earthed (so I learned in my studies) so that you get schocked and know that electricity is dangerous (no joke) AND because in a neighborhood e.g. someone would be touching a live phase and someone else another, so that both would be exposed to the line to line voltage which is

380 V in Europe (220 V in USA).However this happens only in LV, in MV, HV and EHV there's no need for a reference to ground, because the windings of the substation transformer are in delta, ungrounded.This doesn't make the voltage not dangerous, I was told some horror stories back in Kozani.

-- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr Ï "Scott Dorsey" Ýãñáøå óôï ìÞíõìá news:d7k9da$83a$ snipped-for-privacy@panix2.panix.com...

Reply to
Dimitrios Tzortzakakis

They are often grounded even so, sometimes through a resistor and current measuring equipment to monitor leakage in the line. Also to prevent a transformer leak letting the lower voltage windings float up to the voltage of the HV windings relative to ground, which would exceed the insulation rating of the line and downstream gear.

Reply to
Andrew Gabriel

In alt.engineering.electrical Scott Dorsey wrote: | In article , w_tom wrote: |> Ioslation transformer must still have the secondary (the 120 |>volt side) connected back to the building safety ground. If |>not, then the appliance will 'float' - can become electrically |>hot. If the transformer is properly designed, then either it |>has such a connection OR it has a dedicated grounding wire |>terminal to make that necessary connection. | | No, that's the point of isolation. Because the appliance floats, it can | become "hot" but the leakage current has no reference to the building | ground so if you touch the hot case, no current will flow through you. | | Not that a safety ground isn't _still_ a good idea, mind you.

Except for low voltage lighting, according to NEC article 411.

Reply to
phil-news-nospam

If a transformer is properly grounded as required by codes, then if the appliance has an internal short, that short will trip a circuit breaker. Grounding transformer secondary is necessary for breaker to trip. Leakage across to a floating transformer secondary may put enough voltage on chassis to cause shocks - with or without an internal appliance problems. But transformer secondary must be safety grounded - as codes require. When grounded, further useful information (ie a tripping circuit breaker) would then tell us more, immediately eliminate any human safety threat, and cause humans on the scene to fix any existing problems. Even if the appliance does have an internal fault, that fault would not be fixed because a transformer secondary is not grounded.

BTW, I have assumed the appliance has a three pr> All those observations seem all for naught to me, since he as a Hot > Chassis Item.

Reply to
w_tom

--------------- In LV, MV , HV and RHV. the transformer windings can be and often are in Y.- . The most common connection is Delta Wye with the HV side in Wye with direct or impedance grounding. There are good technical and economic reasons for that. The next most common connection is probably Y-Y -delta for supplying EHV lines . Note that even at 4160V distribution the supply transformer is Y on the 4160V side. Ground faults are the most common faults on transmission lines. This means that the unfaulted phases will see overvoltages- not good. In addition, protective relaying problems are increased and arcing faults which are not detected and often undetectable can occur because of capacitive coupling. The grounding eliminates these problems as well as problems due to the line floating up and down due to atmospheric effects (thus stressing the insulation). The use of a Y system makes life a lot easier.

Reply to
Don Kelly

Sorry, given that it was e-bay, I didn't cjheck the origin. The solution that I suggested was for North American usage. The key in the UK case is to pitch the original transformer and get an isolation transformer (2 winding 120/240V)

Reply to
Don Kelly

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