hair stands on end when i touch the case!!!

[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]

Originally Posted by draughted 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]

Originally Posted by draughted 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]

Originally Posted by 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.

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