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Why do I get a shock or Tingle when I touch the VCR's RCA connectors ?

Current from June 19th 2006 - This page needs no introduction.

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220 ~ 230 ~ 240 Volts Mains Power Power Supplys

Back in the days of "REAL" transformers, all electrical and electronic appliances were internally " Earthed "
or " Grounded " at their internal metal chassis via the Green Earth wire within the power cord to the mains GPO,
 ( General Purpose Outlet ).   Back in those days, the wiring colours were RED ( Active ) , BLACK ( Neutral )
and GREEN ( Earth ).    Therefore, in accordance with international trends and standards, the Australian
wiring code of colours became Brown ( Active ), BLUE ( Neutral ) and GREEN became GREEN / YELLOW
stripe for the Earth wire.

Three wires entered into the appliance via a " cable entry device " which facilitated a good mechanical
support to the wires and cable restraint acting upon an " Energy Authority " approved 230 Volt 3 wire cord.

The earthing wire which, when traced all the way back to the meter box, was in fact earthed inside the
consumer's  " fuse box " or  " power box " then down via a thick green wire to an earth stake driven into
the soil, usually directly below the power " fuse box " installation. Reasonably damp soil is desirable for
good conductivity.

A typical Australian 3 core 230V cable

As described above, this should be typically a moist area to facilitate good grounding into the soil.
Now, having said that, we here in Australia, use what is termed M.E.N. system, or Multiple Earth Neutrals,
which is a fancy way of stating that the neutrals all end up in the meter-fuse-power box all connected to
the earth wire to ground.

The water utility added in a plastic isolator between the street main water supply and the domestic or
business user thus resulting in incoming the water pipe being totally " isolated " from the street except
by the conductivity of the water within. We believe this concept is to drastically reduce lightning penetration

The appliance, both electrical and electronic would have the earth wire connected directly to its chassis,
thus forming a safety earth return should any problems occur with that appliance.

This concept is still a fairly good system, which is why professional equipment manufacturers have adhered to it!
Thus, if something happens to cause any sort of conductive path from the Live ( or Active ) side of the 230 Volts
mains supply to the metal chassis,   then that " fault " current is conducted directly to earth or ground.

If the impedance of the fault current is low enough a large current will flow and usually cause that particular
equipment's " protective " fuse to blow, disconnecting the active leg of the 230 Volts mains supply and thereby
signaling that something is very wrong, by the absence of appliance's indicator LEDs, Neon indicator or pilot
lights or just plain not working at all. In some cases, professional equipment may have a "blown Fuse" indicator.

Looking at Hi-Fi set-ups and P.A. ( Public Address ) systems,  it is not uncommon to have a noticeably audible
50 Hertz ( or 50 cycles per second of sine wave) mains hum ever-present. This can be very annoying to hear.

In dedicated distributed video systems a 50 Hz hum can present itself as a visible light and dark horizontal bar
moving slowly up and/or down the video or television screen.
If the hum is too severe, it can disrupt the synchronisation signals and, in some extreme cases, cause major
distortion of the TV or video image. Often in bad cases, "tearing" at the top or at the bottom can be observed.

A representaion of a 50 Hz Sine Wave

It is a common ( stupid ) practice for "totally ignorant" ( read - morons ) persons to disconnect the mains earths from
various items of equipment until the hum ceased. This practice must cease. Death by wilful disconnection of any
earthing wires in any system is a serious offence and should a person die as a result, expect a long prison sentence

SERIOUSLY FOLKS, THIS IS A VERY DANGEROUS, POTENTIALLY LETHAL
AND A VERY STUPID, DEADLY THING TO DO. YOU HAVE BEEN WARNED !

We repeat the warning here, coming in contact with 230 volts AC mains will kill you dead !


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One of the stupidest examples is that some Rock n' Roll singers and performers have suffered severe
electrical shocks and in some cases, electrical burns to their lips due to the total ignorance of their
"technician" or their "roadie", who has removed the earth connection from their guitar amp thinking
this will stop the audible mains hum.   This is lame, very lame indeed and in fact, as mentioned,
very dangerous !.   If you find someone doing this, you know what to do. Tell them and then Sack them.

What they fail to realise is that there is often a mains filter typically consisting mainly of two 400V or 630V
rated polyester capacitors, one from the Active 230 Volts side of the mains to the chassis and the other from
the Neutral side, connected to the chassis.

These are fairly effective at preventing RF interference and in some cases, spikes from entering or leaving
the amplifier, however when the earth connection is broken they form a simple voltage divider with the
centre-tap on the chassis ! Very Dangerous ! and Very Deadly !
Here in Australia, as well as New Zealand and many other countries where the mains voltage is around
the 230 Volts AC mark and this places about 120V ~ 170 Volts AC on the chassis and the capacitors are
usually of such a value that roughly 1 mA to 18 mA of current can flow from the electrified, unearthed
chassis to anything that is properly earthed.

So, when the singer holding their guitar which is solidly connected to the now "unearthed" amp, touches
their lips momentarily to the microphone's grill mesh, which is just as solidly earthed by the PA system,
they get a major shock in a very sensitive part of the body - their moistened lips !....Zap !
The current flows from their hands through their chest and heart to their lips. The current can also flow
across the chest and electrocute their heart, sadly, this usually kills the entertainer on the spot.
The natural assumption is to blame their Microphone or their PA system, but all tests of that equipment
show no problem.

If the guitar amp suffers a serious electrical fault or the capacitor in the Active line shorts out, which
incidentally they do " short-out " sometimes, the entertainer or performer could sadly and easily be killed.
This has happened before. This is not a CSI reality show, it is deadly serious.

DO NOT EVER DISCONNECT A MAINS EARTH UNDER ANY CIRCUMSTANCES !


Double-insulated equipment is not connected to the mains earth and most of the Hi-Fi and Video gear intended
for the domestic user is double-insulated.

Typically, the cable ( below ) whereas only two wires is used to power the appliance, the neutral is used as
a " pseudo-earth " as in the "meter box, where the neutral is in fact connected to the earth. the M.E.N. system

A typical 2 core 230V cable

In double-insulated gear the metal chassis is connected only to the "common" side of the circuitry to
achieve some shielding to prevent RF (radio Frequency) interference from radiating into or out of the item.

There can be no mains filters which connect to the chassis, so at least the chance of a shock from this cause
is eliminated or at least basically minimised.

It is easy to identify double-insulated equipment because the mains power lead will often be flat instead of
round and the mains plug will only have two pins and there may also be a symbol on the chassis - two concentric
squares or put simply, a square within a square molded into the appliance's case indicating double-insulated.

The DOUBLE INSULATED logo      The Double Insulated logo      The DOUBLE INSULATED Logo

So what can go wrong with double-insulated gear ?????? ........ Plenty, ...... as we shall now see.

All electrical equipment contains a mains powered PSU ( Power Supply Unit ), unless it is using a "wall-wart"
with an actual small transformer within its small case. Some models of the conspicuous "wall-wart" employ a
switched-mode mini power supply, which, here again, has its own "leakages". It is a trade-off, cost V's efficiency.

The PSU (power supply unit) converts the raw 220V ~ 230V mains into low voltages for the equipment's circuitry
and isolates the mains from the low voltage side ... well ..... almost.

You see, all power transformers, whether they are designed for a switch-mode supply or linear supply, they all
leak a "small" amount of current from the primary to the secondary board earths due to stray capacitance.

In double-insulated items there is no "REAL" earth as in earth to "GROUND" per se available to use as a shield
between the input and the output, so the power supply is designed as far as possible to minimise the leakage
due to this unavoidable "leakage" effect.

Unfortunately, switch-mode supplies run at very high frequencies, so the smaller capacitance in the smaller
transformer ends up leaking just as much as the larger capacitance in a larger transformer running at 50 or
at 60Hz for example.

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LEAKAGE ? uh ?......

The leakage current is usually less than 1mA and is often as low as 10uA, but even at such low current, it
can still present and still can cause problems.

Generally as a rule of thumb, the more power an appliance uses, typically the higher the leakage will be.
Things that use an external power supply typically plugged into the wall's 230V AC GPO (General Purpose
Outlet) are not exempt either.

These power supplies are usually double-insulated and leak just like anything else connected to the mains.
Insects, dust, moisture, food particles and all sorts of miniscule bugs find their way into most electrical
equipment.

Digressing a little here,.... we have noted over the years that some "silicone based" sealants use to "hold"
electronic parts actually attract ants, black small ants that set about to devour this set silicone.

Electrolytic capacitors and batteries can leak their corrosive contents and components can overheat or be
damaged in a million other ways.   Do not dispair, it is not all glow and doom. Most elelctronic equipment
lives on past the warranty period and in some cases, well past the "extended warranty period also.

Insulation gradually loses it's "plasticiser" due to age, exposure to UV light and heat from thermal cycling
to mention just a mere few causes and becomes brittle.   Insulation in transformer windings degrades
over time due to vibration and heat.  Unless all the "lams" (laminations) are secured by a transformer
lacquer or are screwed together tight (in the case of E-cores) the laminations will vibrate over a period of time.

All these things can conspire together to cause electrical leakage (or even short-circuits) to the unearthed chassis
of double-insulated gear and, guess what ? All of a sudden it's not insulated at all !

Crappy or rather poorly designed PSU designs also can contribute to the lengthy list of usual suspects.
The introduction of an earthed item into a system made up of double-insulated gear is not unlikely, but it is
somewhat likely to be the start of some " interesting " problems.

Let's say you have a DVD player, two VCR's, a TV/Monitor, a CD player, a cassette deck, a Pre-amp, a Graphic
Equaliser, ..... I think you get the idea .......
All these things are double-insulated and they are all connected to each other either directly or through
one of the others.  The leak current all adds up.
It would not be unreasonable to expect any where from 0.1 mA to 1.0 mA ( or even more ) of leakage from the
combined equipment because the leakage currents simply add together and increase the figures.

If you were to connect a digital multimeter between this pile of gear and the chassis of your new item, let's
say it's a big brute of a surround sound amplifier which just happens to be earthed, you will measure a very
significant ac voltage, probably at least half the mains supply or even higher.

( Don't try to measure the current, you might blow up your multimeter if there's a bad fault or worse, Kill yourself )

Now, let's say you have the metal shell of an RCA on an audio cable which is connected to an output on the
unearthed gear in one hand and you steady the amplifier with your other hand as you start to plug it into an input.

As soon as you complete the circuit between them you will get a mild electric shock, we have read on our Digital
MultiMeters, (three were used to get the average) 105 Volts AC at about 15 Milli Amps. Nasty little "bite" from it too.

Depending on how moist your skin is and how high the leakage is this might be unnoticeable or it might cause
you to more than likely say a bad " $@^%& " word !

Unless you have a bad heart it is unlikely to hurt you physically, but it can give you quite a sting, especially
when you do not expect it.

Once the first connection is made and the leakage is flowing to ground, there will be no more tingles.

We repeat the warning here, coming in contact with 230 volts AC mains will kill you dead !

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A Typical Australian mains power plug

OK so far .... HUMMING ALONG ......

You might notice though, that your previously hum-free system is now humming and quite annoyingly.

The hum might be affected by the volume control on your amp or not or it might only record on tape or it
might be visible on your TV or ... so,....What do you do?   That's a very good question and one which
deserves a really good answer.  Unfortunately, there is no real simple and easy answer, but now that
you know a bit more about where the hum comes from by now, an orderly and logical disconnection
and re-connection of the whole system will locate the major culprit.   With the assistance of a C.R.O.
( Oscilloscope ), anything greater than 1 MHz is fine.  Work with what you have, this is a very good thing.

MEASURING THE HUM ......  AN OSCILLOSCOPE TO THE RESCUE

Generally the higher the "MHz" Mega-Hertz (million cycles per second), the better the measurement, we use a
60 Mhz Hitachi V680 triple trace with on-screen-digital display, but a simple 10MHz C.R.O. will do just as well.

It is important to bare safety in mind.   We use an isolated mains supply, that is to say, we have two 4A transformers
wired secondary to secondary, ( 26 Volts AC to 26 Volts AC ) 230/240 Volts AC in and 220 Volts AC out.  We chose the
AMIGA A500 power supply for two reasons. (A) They are 240 V AC input rated and they have multi-tap voltages output
voltages on the secondary and the 26 Volts AC secondary is rated at 4 Amps output current, which will do the job quite
adequately.  (B)The second was we had them here as left-over service stock items and we may as well use them.

These came out of AMIGA A500 Power Supplies and were easily fitted within the A500 power box case.  The output
is a flying 3 pin plug (AUSTRALIAN) and 200mm of lead.  This lifts the CRO above mains potential which is the safest
for your equipment and for personal safety reasons. Most transformers can be paired / wired secondary to secondary,
preferably "fused" and at least over 2.0 Amps to be able to provide enough " grunt " in Amps to drive your CRO.

The reasoning here for being greater than 2.0 Amps, is the oscilloscope may draw larger current than you may
and this could create an overheating problem in the primary windings and naturally a much lower output voltage
than you perhaps expected. As mentioned, we chose a 4 Amp pair of transformers and these work fine under load.

Below is a simple example of how to make your own "ISOLATION TRANSFORMER".  In essence, two AMIGA A500
(heavy brick) power supply transformers were chosen for our own personal heavy current applications for testing
under relatively safer working conditions.  The small power regulation PCB along with its heat sink was totally
removed and the extra transformer was placed inside and stuck down with" silastic" making it adhere to the plastic
A500 PSU case.  The existing ON/OFF switch was used as well as the original 230/240V AC power in cable.
A 2 Amp fuse was incorporated between the active wire "switched" and the primary T1 transformer for safety.
As a prime safety requirement, both transformers must be earthed to the original 3 wire cord (Green / yellow wire)

Here in Sydney, our local mains supply is often sampled prior and during testing to see what voltage is currently
being fed to our equipment and we have often found 242 Volts AC measurements made on our trusty "DMM" Digital
Multimeter.  Yet we have been fed information that the mains voltages are now 230 Volts AC as a standard and not
our " old " 240 V AC standard since it was introduced as the " norm " here, well over 120 years ago.

A simple Isolation transformer diagram

If you have been unlucky, you might also notice that first input you plugged in is now " noisy " or " distorted " or
just plain not working at all.   If all else fails, read the Manual.   Ever wondered why they say in the instruction
manuals state that you should totally disconnect the power when making or breaking connections to anything ?

Well now you know! It's to avoid shocks, huge hums, loud crackles and damage caused by high voltages being
connected to sensitive inputs before the common/earth/ground side manages to short-out the dreaded mains leakage
or possibly your own static-electricity build-up from contact with nylon or plastic in walking).See the 3M manual.

Read the 3M manual devoted entirely to this subject so you do understand what you are about to do.  Play "safe",
and always read your manuals on how to operate equipment safely!  These manuals are written with your safety
and best interests in mind.  Please familiarise yourself with all facets of correctly operating your equipment

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It might be a nuisance, but it does avoid all these problems, and could save your life (or at least that of your
other gear) if one of your double-insulated ' what-ever' happens to have a serious electrical fault or a bit more
leakage than your other equipment can tolerate.

Lastly, this tale, only one of so many, it has to be told .... so one day,  one of our newer customers rang us one
day to order some special length VIDEO and AUDIO cables.   Nothing strange about that, however his next request
had me indeed quite intrigued as well as very puzzled - the customer wanted the cables totally insulated, that is,
with no exposed metal anywhere.

I questioned him as to "the thinking" behind this and asked why,  his quick reply was "Because he gets really bad
tingles and mild shocks from exposed connectors from his video editing suite and his TBC ( Time Base Corrector ),
when he re-configures the Video or Audio wiring to other video equipment he wishes to utilise".

So, upon further questions, I was informed that he had 4 ordinary VCR's, a TBC (Time Base Corrector),
a Genlock and several Philips 13" Audio/Video monitors as well as his computers.  The computer
and the Genlock were the only items that were earthed during manufacture, all other equipment he used was
of the " double insulated " floating above earth types.

And Sparks may fly ....

At one stage, a "bright spark" suggested that he remove the earth wires from both Genlock and computer,
which of course would do nothing and make the whole setup totally "floating" above earth potential, I
conveyed to him that this suggestion made me truly horrified and explained that the results may contribute
to the deaths of some-one later down the track.

I arranged for " house-call " by a colleague to visit him, he is a technically competent electronics technician
and a very electronically " savvy " friend of mine who's job it was to " go over " his setup and in consultancy with
myself.   we ended up attaching 0.22uF Class X2 400V AC poly caps to the rear of each VCR's lid temporarily as
shown in the two drawings below ( undo the screws and add in the caps with an "earth lug" ), this also preserved
his 4 VCR's warranty ( nothing needed to be added inside ) simply a "lug" under a screw on each device.

This rectified his zapping problem, the AC present was to the order of 127 volts measured by a DMM and a CRO
( Cathode Ray Oscilloscope ) with about 27 mA ( milli Amps ) of current flow measured on the digital multi meter.
Some may say this is am inherent acceptable situation found in switched mode power supplies. We reject this
concept.  While is can be argued that With better filtering, improved design applications and choice of
voltage controlling semiconductor components will improve this problem, it all comes down to mass-production
costs.   The bottom line is always costs. How much is the consumer prepared to pay for a correctly designed item ?

2 VCRs connected in a simple way to reduce sparks

This certainly assisted in getting rid of the considerable leakage of the 4 VCR's and the T.B.C. contributing to the
mild electrical shocks and some of the hum.  Oh... to live in an electronicaly perfect world !

You will note that for absolute simplicity, I have drawn 2 VCRs with bare components shown, this is NOT how the
completed item should be wired and all items should be housed in a safe and sealed plastic box.

It would be electronically better to place all parts in a very small " jiffy " box with double sided tape or VELCRO
all from either Jaycar or Altronics or your local reliable Electronics specialist supplier in your country.

The 0.22uF class X2 capacitor should be wired up as shown in the small drawing below and it is a good idea
to connect all the earth bound wires into on 230V plug.


              The Parts list.
                 1 x 3 pin mains plug (wire all earth wires in last of all).
                 1 x 22nF ( 0.22uF ) Class X2 polyester capacitor rated at 400V ~ 630V AC.
                 1 x Small plastic box,about 50mm x 100mm x 80mm or similar 
                 1 x crimp "ring eyelet" per appliance, 2 appliances ? Two will be required.
                 1 x 2 way mains block per appliance.
                 1 x strip of double sided tape (or velcro tape).
                 1 x small nut & screw 10mm to hold the terminal block.
                 1 x strip of 10 terminal blocks, cut into two per box.
                 1 x length of 230V mains rated flexible green earthing wire,
                 1 x Mains surge protector power board to suit all your devices.
                 4 x small cable ties.

              NOTE: You may want to consider the additional circuit concept (below) as a adjunct protection.


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RCA ZAP FIX

Above, you will note ( Fig.3 ) the simple representation of a RCA connection, note at the video cable entry
( on the left ) it is connected to the "hot" tab of the rear of the RCA female connection along with a 5.6 Volt
400 Milli-watt zener diode, this also we have found to be an excellent clamp against those nasty " bities "
that are often encountered with connecting to RCA connectors on " switched mode " powered electronic
equipment which comes out of South-East Asia and widely used these days.    Hey ! ..... It works.

               The Parts list.
                  1 x 400 Milli-watt 4.7 Volt ~ 5.1 volt, a 5.6 Volt zener diode being the Maximum.
                  1 x Small amount of solder to be skillfully applied.
                  1 x Time to correctly and carefully do the job correctly.

                Note: The addition of several 5.1 Zener diodes on all RCA sockets did in fact "clamp and stop the "Biteys"
                from sparking when connecting other switched-mode devices.    It was amazing actually, one did not need to 
                dim any lights to see the actual " small sparks " that passed from the VCR or DVD player to the RCA cable.


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           are not subscribed to by the Unitech Electronics web site.   In Australia mains 230 ~ 240 Volts A.C. 
           does in fact kill you. You do not get a second chance. Do not play with mains power.

           We repeat the warning here, coming in contact with 230 volts AC mains will kill you dead ! 

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