[draughted]

hi guys, i have recently re-wired the control box for my machine and found once again that the hair on my arm stands on end with a very definite tickle sensation. it was one of the reasons that i re-wired so i am a little worried it is my fault in wiring.

does anyone know this to be normal. what fixes do you know of.
i have used both torroidial power-supples with full-bridge rectification as well as
switch mode supplies, and they both seem to have the same effect.
is my earthing inadaquate.

i don't want to electricute myself any more than i have to.

[aussiegazza]

Try earthing the case as well.

If you must use an earth leakage detector (ELT) where you are located, a leak to earth should blow the ELT and you will know you have a short from either active or neutral.

[aarggh]

This is really dangerous, if your actually getting a tickle have you inadvertantly crossed the active with the neutral? You should be able to check this with an ohmmeter from either one to the ground connection.

Have you also done a proper star earth layout (everything should be earthed!), this is critical to stop multiple earth paths and voltage differentials.

cheers,
Ian

[draughted]

yeah thanks for your concern. i go to great lenghts to star earth every thing i wire up.

with the case in question i have an earth coming from the plug socket, pop riveted to the chassis along with the earths for the three switch modes present in the case.
it could be something i have missed but i can't put my finger on it.

what was that you said about swapping live and neutral?

[aussiegazza]

yeah thanks for your concern. i go to great lenghts to star earth every thing i wire up.

what was that you said about swapping live and neutral?

Check your wiring VERY carefully. All the way from the wall plug (check it too) to the machine's connections.

I will not tell you colours etc as they can vary (Update your OZ) over the last few decades or so.

In Oz, Neutral is connected to earth at the distribution box, and earth is run to an earth post. If you have active and neutral wrong, you can be making anything earthed LIVE. An earth leakage detector should stop this happening though. You may not have one.

Check it visually before you turn it on again.

[aarggh]

what was that you said about swapping live and neutral?

In the place we bought some time ago, we used to get a very slight "tingle" when we touched the electric kettle and the sink. It took a lengthy hot spell for it to go from a slight "static" kind of feel to a genuine shock, due to the ground drying up, as the earth wasn't properly connected to that socket, but while the ground was moist, it was enough.

I put a meter on it and it measured 125 volts roughly. The power point feeding the kettle had been wired by the previous owner, and i'm guessing he made the classic mistake of live/neutral connections relative to male/female sockets/plugs, and had transposed the active and neutral on a power point. This meant whenever the kettle was on, it was fed from neutral, while the active was connected to the earth, hence the shock!

Very simple mistake, and no doubt common, but I really can't underscore just how dangerous it is! It can put you and anyone else you care about in danger.

If you have ANY confusion at all about wiring, please ensure you google as much as you can, especially regarding earthing, and earthing stakes and their roles, as you may only get one chance. Electrical wiring really isn't hard at all, you just need a basic but good understanding of it. Also think of how others may be at risk. For example, if you'd transposed the active/neutral, and someone were walking around barefoot on a humid day, the risk of being electrocuted could be quite high. Rubber soled boots, dry air/ground, and many other factors can all mask a potentially lethal situation, that may only manifest one day when its been really hot, the earth stake may need replacing, etc, etc.

For a few bucks you can little electrical testers that plug into your socket and will light up according to whether the the cables are shorted, crossed, correct, etc. While not infallible, I would highly recommend them as a first point of helping to determine if there is a problem.

Good luck chasing it!

cheers,
Ian

[Al_The_Man]

You either have improperly grounded system at the machine or your supply panel system ground is defective, i.e. one side of the supply is not grounded.
It should not matter how your connections are made, a properly grounded system you should not have any potential to ground from any metallic part of the machine.
This is normally qualified by an electrician using a resistance Megger, (not a high voltage insulation type), the resistance type is used to measure earth ground path resistance.
Al.

[draughted]

well thanks guys, i think i will be getting the electrician neighbour around to check the earthing points.

i'll keep you posted.

[john-100]

in water heaters and kettles its normal to have some leakage current to earth !

so the electric shocks are a warning !

are both the kettle and your machine plugged into sockets installed by the previous handy man ?
the earth connection could be missing

even when wires are in metal conduit ,an earth wire should be installed
you can have high resistance at the conduit joints

the neutral cable is connected to earth at the supply transformer
( usually the star point of a 3 phase transformer)


if your earth and neutral terminals are only connected at the transformer

the earth connection can be either a wire in the cable or the steel armour
in which case you can measure a small voltage between them
( ie the volt drop in the neutral supply cable)


earth leakage / residual current breakers monitor the difference between the live and neutral currents , usually tripping at 30mA

the mains filters inside switch mode power supplies also leak to earth
and supplies without an earth like those used with I.T. equipment
leak to the output !!!!

when you use several together its enough to feel (got the T- shirt)

John

[mike_Kilroy]

nobody has stated the obvious probably because it is obvious: have you put a voltmeter from that case and the other lead to a good known ground and MEASURED it? Do both AC and Dc scales.

[draughted]

it would seem i am in ignorance.
i asked you to elaborate on active and neutral swapping purely because i over looked the significance of it when i did the thing.

i have now taken the internal wiring back to basics and i can confirm that active and neutral were wrong at the socket and the significance is now sinking in. my basic knowledge of AC current defied the fact i don't know everything and lead me to believe the two could be switched.

[aarggh]

it would seem i am in ignorance.
i asked you to elaborate on active and neutral swapping purely because i over looked the significance of it when i did the thing.

i have now taken the internal wiring back to basics and i can confirm that active and neutral were wrong at the socket and the significance is now sinking in. my basic knowledge of AC current defied the fact i don't know everything and lead me to believe the two could be switched.

This is a surprisingly common mistake as I mentioned in my post with our power socket, it's good you found it as it can be very, very dangerous. I've also seen this happen heaps with home made power cords over the years, as people when making extensions visually get the perspective of the pins messed up and transpose active/nuetral on one end.

cheers,
Ian

[Al_The_Man]

i have now taken the internal wiring back to basics and i can confirm that active and neutral were wrong at the socket and the significance is now sinking in. my basic knowledge of AC current defied the fact i don't know everything and lead me to believe the two could be switched.

That should not make any difference on a properly grounded system, IOW there can be no potential between frame and ground whichever way it is connected?
IMO You may have disguised a still potential problem.
Al.

[john-100]

with the live and neutral swapped at the socket

any circuit controlled with a single pole switch will all ways be live!
but would appear to work correctly

but if the live and neutral supply to your house has been crossed AND
your earth and neutral terminals are linked together ,your in danger
the mains earth will be live ! look at my diagram in my prevous post

check for any voltage between the mains earth and an earth rod

check for any breaks in the earth wiring
if the live an neutral are wired wrong who ,knows what state the earth wiring is in

John

[Al_The_Man]

It is impossible for a machine frame to have a potential to earth ground when correct practices are performed.
Regardless of the polarity of the wired socket.
Ground Practices
The mains earth cannot be live as both conductors are identical before grounding and it is arbritrary which one you pick for neutral!
Al.

[john-100]

I agree Al
If wired correctly


another link to earth / ground systems :-

Earthing system - Wikipedia, the free encyclopedia

a bit of a minefield , you need a copy of the regs for your part of the world


John

[mike_Kilroy]

It is impossible for a machine frame to have a potential to earth ground when correct practices are performed.
Regardless of the polarity of the wired socket.....
Al.

Which brings out the point: the machine was not wired up correctly: ie., IT COULD NOT HAVE HAD A GROUND WIRE FROM THE MACHINE FRAME BACK TO EARTH GROUND AS IT SHOULD. Or the moment you applied power that reversed polarity would have had to go to ground and would have popped your circuit breaker or fuses.

Draughted, you want to be sure to add this missing ground wire in addition to correcting your polarity! If you have any questions about how to add this wire, post them here - we don't want to hear that you fried yourself down the road a piece!

[Al_The_Man]

Which brings out the point: the machine was not wired up correctly:

Yes my point.

OK, lets start from the beginning and go over some fundamentals.
We start with a two 1ph AC conductors with a voltage 120vac or 240vac as the case may be, i.e. two conductors which at this point are indistinguishable.
We decide to make one a 'neutral' by virtue of connecting it to Earth Ground, we connect this supply to an AC load, being AC the load is not polarity consious.
We conect the ground wire to the case of the equipment, in the event of a leakage from the 'live' conductor to the frame, due to there being an ideal resistance of zero ohms between Earth ground (machine frame) and the neutral, current will flow in the ground wire but as the resistance is close to zero there will be no potential between case and ground, if the leakage is of sufficiently low resistance the result will be a blown fuse.
Changing the polarity of the incomming supply will not change the condition, just that depending on the nature of the leakage, the neutral could be now close to be connected to the machine frame, although having no shown symptom, is not desirable.
So doing disguises the leakage error.

BTW, I did some tests a while back on N.A. equipment that uses heated water such as Kettles, Steam Irons etc and is factory fitted with a 2 pin plug.
I measured between 3v and 26vac from the metallic surface to a known ground, this is not suprising as the meter used was a high impedance VOM, and was most likely measuring inductive or capacitive leakage.
The clincher as to how safe this is, is how much current the apparent voltage will support, if more that a few ma's then it can be dangerous to human contact and the appliance should be regarded as defective.
I placed a test resister of varying values between the leakage and earth and the voltage collapsed to an insignificant amount at very low current.
If you can feel an tingle when touching an external surface, then this is definitely in the problem range.
Al.