I think our company fields machines that can shock people. Can I try to fix it?
If the shocks are large and muscle grabbing then the explanation below is NOT the cause and the source should be sought with care. However, there is a reasonable chance that the cause is as follows. 

IF the equipment has NOT got a ground lead and/or grounded 3rd pin in the mains power socket then noise filter caps in the equipment (connected from both power leads to equipment ground) can cause the equipment ground to be at about half mains AC voltage BUT at high impedance. 

The shocks received from this source are annoying but probably not dangerous.  

In the left hand image below the Cx and Cy noise filter capacitors connect to the metal case which is connected to mains ground (PE).  

If the connection to mains ground at PE is removed then Cx and Cy form a capacitive voltage divider across the mains and the metal case is at about 1/2 Vmains. Cx and Cy are typically 1 nF and the current available is below what which is deemed a cardiac hazard by most regulations. The shock which can be received is annoying and the voltage can damage electronic equipment.  

Adding a ground lead remedies the problem. 

From Wikipedia image here



Providing a ground wire to eqpt metal parts will fix the above problem. This SHOULD be via the mains outlet but a wire to local ground will work much the same. There is some small risk that the wire to random ground will increase the hazard - but unlikely. Wire to power point ground should be safe. 

The following answers that I've given to other SEEE questions address the above capacitor related issue: 


Electric shock from laptop due to capacitive coupling?     
Why would a power supply unit with insulating case and galvanic separation need a grounded power cord?     
Plug in charger in laptop before plugging in mains outlet    
USB port and bench power supply ground difference


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Q&amp;A:

Misunderstaood said


If someone is getting shocked the voltage is high enough to potentially be lethal. Non-lethal voltages generally do not give shocks with dry skin. 9V will tingle on the tongue. The reason they are not electrocuted is usually due to low skin conductivity. Over 100V is considered lethal. Lethal is more a function of body resistance and current path through the body, e.g through a heart muscle


A: IF the mechanism is the two Y capacitors then by design and regulatory requirement the current is low enough to not cause atrial fibrillation (or any other cardiac issues) in several standard deviations from the mean population - and possibly quite a lot more than that. I'm not saying that it's a good idea or that it shouldn't be fixed. 

The impedance of the capacitors is the main factor in current magnitude with a well grounded user. Current is ~~~&lt;= 2.Pi.f.C.Vpeak or around 0.1 mA per nF with 230 VAC mains. Earth leak breakers designed to meet regulatory requirements to protect against cardiac arrest typically trip at 30 mA imbalance (higher than I'd consider wise). Even at 10 mA trip that's about 100 times what will be obtained via the Y caps on 230 VAC. 

I'm personally unhappy with the 'higher than previously' limits set for AC &amp; DC ELV in recent standards, despite the technical explanations given as to why they are appropriate.