Bathroom cabinet electrical shock?

[deano]

Its a metal (stainless steel) casing with a mirror door, has a canopy over the door with 2 low voltage downlighters recessed into it. The lights are operated via a rocker switch at the top rh =A0side covered in a rubber membrane. The whole thing is shiny mirror like metal finish inside and out. I have an isolator switch mounted on the wall in the room behind it. It's above a wash hand basin in my downstairs shower room- where I shave.

With the door open, as I put my hand in to get my shaving foam, I get a small electrical shock, on the back of my arm, just below my elbow, where it touches the corner of the open door! It's a constant 'buzz' - not painful, but uncomfortable and obviously worrying!

How can I go about finding the fault? It happens when the isolator switch is on or off! I'm wondering if the unit is faulty or has a fixing nicked a cable in the wall? It's been up for a couple of Years and only when the missus mentioned getting the same shock have I thought I'd better get it resolved :)

[Ret.]

I'll leave the electricians in the group to answer your query - but on the issue of the 'buzz'... When my wife's iPod is on charge (using a non-Apple compatible charger), if you pick it up and run your finger lightly over the metal surface, there is also this 'buzz' sensation. I wouldn't describe it as an electric shock - just a very very mild 'tingling' sensation.

As the output of the charger is low, I am assuming that there is no danger from this...

[deano]

Yep... 'A mild tingling sensation' also is a better way of describing what I'm getting.

Btw: using google groups on my iPhone is very Frustrating- is there an app available that would make using this ng any easier? Anyone? :)

[Tabby]

Equipotential bonding would solve it. I cant comment on the risk of the situation, as I dont know if its filter capacitive leakage or cable damage. One's harmless, one liable to be fatal.

NT

[Geo]

Depends what test equipment you have (DMM, Avo etc)? You really do not want to be using a wet finger to fault-find.

Does the wiring from the isolator to the transformer (assumed in the cabinet somewhere) include an earth wire? If so, is it connected to the metalwork? Continuity? I would have expected the isolator (FCU?) to disconnect the line from the transformer so there should be no leakage possible.

[Andy Wade]

These 'tingles' are usually the result of capacitive leakage between the mains and the case of a Class 2 ('double insulated') appliance. The relevant safety standards usually allow up to to 0.5 mA leakage at 50 Hz (more at higher frequencies). It's completely harmless [*] but can be annoying and/or worrying. (The 'return' path for the current is via the body's natural capacitance to earth, typically a few hundred picofarads.) It's becoming more common with the move away from iron-cored transformers to switch-mode circuits in wall-wart PSUs - a consequence of the WEEE and EuP directives.

With a high impedance voltmeter (any DMM these days) you'll typically measure 100 volts or more between the case and earth. The source impedance of these errant volts is very high though, and just touching the case will lower the touch voltage considerably. Temporarily earth the case via (say) a 10k ohm resistor and measure the voltage across the resistor if you want to get an idea of the available touch current.

Unless there is a fault, no.

[*] One case to be aware of is where several items of Class 2 AV equipment are interconnected by the signal wiring. Here the available leakage touch current will add up and can reach dangerous levels (>3.5 mA is considered dangerous, >10-15 mA can be lethal). Earthing the system (either directly or via a resistor) is advised in such cases.

[Andy Wade]

If the cabinet is a Class 2 appliance it shouldn't be earthed to the CPC of the wiring. The CPC should be terminated, but not connected to anything. Local supplementary bonding could be used to kill the tingle though, if desired.

If it's Class 1 and in the Zones it should be earthed and bonded (unless the 17th ed. bathroom bonding exemption is being used). However any tingle from a Class 1 appliance should be investigated as it tends to suggest that the earthing has come adrift.

Yes, that's the worrying bit here. The 'problem' should completely stop when the isolator is open. Cable damage within the wall before the isolator could be indicated. Definitely "requires investigation," I think.

[dennis]

Google shows a lot of hits.

E.G.

have no idea what they are like as I don't have, or want, an iPhony.

[Tim Watts]

I would stop using that charger right now!

At least get it tested. There should not be enough leakage to cause any "buzz" sensation, which is clearly mains leakage and not a static shock.

You have to ask yourself, "what if the leakage path in the device worsens, suddenly, due to component breakdown". The fraction of a mA or so you are feeling could suddenly become several 10's of mA which is borderline lethal depending on circumstances, constitution.

To the OP - same applies. Isolate the lights and get it checked.

[Tim Watts]

Exactly.

We don't know what's causing the problem, but there is a chance it could be something that could fail into becoming extremely dangerous.

Risk assessment mental exercise:

1) Dangerous condition not proven but suspected: outcome potentially devastating

2) Inconvenience of isolating suspect circuit - sod all.

Makes it a no brainer - turn it off and check it out.

[John Rumm]

Can you see if there is a ratings plate or other markings on it? In particular something that describes it as Class I or Class II and/or does it have the Double Insulated logo on it two concentric squares - see first entry of:

How can I go about finding the fault? It happens when the isolator

For clarification - when you mention the isolator - do you mean the rubber coated switch on the side, or the one in the adjacent room?

If the latter, then this is of more concern. What circuit is the fed from? If you turn off that whole circuit at the consumer unit, does that stop the buzz?

Sounds like a wise move...

Its possible this is just a case of capacitive coupling from an electronic transformer for the lights or similar - but it could be more sinister.

[Tabby]

deano wrote

which means we know its not capacitors in the power supply, making the likelihood of a potentially fatal fault fairly high.

NT

[cynic]

fixing screw into a buried cable perhaps? I'd not be tolerating any sort of noticeable leakage in a bathroom/shower situation due to risk to other people than myself.

[deano]

I've experienced similar 'tingles' with a couple of modern appliances at cu= stomers homes during my work and have always wondered what's behind the cau= se. It seems that construction of the appliances would explain the occurren= ce in most cases from what I have read posted here, but the potential for i= t to be lethal is of concern, especially to those with no knowledge of how = these things work! I'm going to isolate the whole circuit and see if the bu= zz persists and will report back with further findings. My belief is that i= t's harmless but I am going to check all the wiring to see if it's sound. I= put the unit up myself and the stud wall it's on including first fix cabli= ng, so I'm sure it's not cable damage. I can bring in a friend to check for= leakages but would also like to know how I can remove the buzz using bondi= ng if the fault is capacitor leakage. Thanks to all for the great and useful info.

[Tabby]

customers homes during my work and have always wondered what's behind the c= ause. It seems that construction of the appliances would explain the occurr= ence in most cases from what I have read posted here, but the potential for= it to be lethal is of concern, especially to those with no knowledge of ho= w these things work! I'm going to isolate the whole circuit and see if the = buzz persists and will report back with further findings. My belief is that= it's harmless but I am going to check all the wiring to see if it's sound.= I put the unit up myself and the stud wall it's on including first fix cab= ling, so I'm sure it's not cable damage. I can bring in a friend to check f= or leakages but would also like to know how I can remove the buzz using bon= ding if the fault is capacitor leakage.

equipotential bondage

[ARWadsworth]

It was the comment that "It happens when the isolator switch is on or off!" in your first post that would suggest that it is not harmless!

Hopefully you will not be using your arm to conduct further tests.

[deano]

Now it doesn't occur with the fused spur 'off'! Could it be residual static that gave this result before? Also, I only ever felt this buzz on the back of my arm where I have more hairs! With no other part of my arm, hand, fingers or Tongue :)

[Tabby]

[Dave Plowman (News)]

Have you got a DVM? If so, set it to 240v AC and measure between the cabinet metal and a nearby tap - assuming it is connected with copper pipe. Or a mains earth from somewhere if not.

DVMs have a very high input impedance and should show anything you feel. You could even try holding one lead while probing the cabinet case with the other.

[Ret.]