Bathroom cabinet electrical shock?

On Sunday, May 15, 2011 9:26:45 PM UTC+1, Andy Wade wrote:

As I've narrowed this to the socket outlet in the utility cupboard, should I use my DMM to check for continuity between this and the fly lead I have going back to the main earth block? Set to a low Ohms level and probe between fly lead and earth terminal of wall socket outlet?

Yes. it is.
best, deano.
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On 15/05/2011 21:41, deano wrote:

Yes, connect one end of the long lead to the main earth block, or the earth bar in the CU. Then check for continuity between the other end of the lead and the cabinet. If you find an open-circuit then locate the broken connection by working backwards along the route of the CPC until you do get continuity.
As you say, use the multimeter on its lowest resistance range, hopefully you should be able to resolve down to under 1 ohm. An alternative is to use a battery and torch bulb, which can be quite revealing of any poor connections.

OK, so it is meant to be earthed. Class 1 and not Class 2, as many of us tended to assume at the start. You certainly shouldn't be getting tingles off that.
--
Andy

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On 15/05/2011 12:41, deano wrote:

You normally just reply at some point in the thread hierarchy - most folks probably have their newsreader software set to show stuff in a threaded hierarchy like:
http://wiki.diyfaq.org.uk/index.php?title=Image:TBWatchedThread.png
which makes it fairly obvious.

ok, these are normally double isolated with only two connections on the input for L&N.

The cabinet sounds like it has an earth to guard against becoming live as a result of a wiring fault in the cabinet, rather than any problem with the transformer.

FSU I take it is a Switched FCU (Fused Connection Unit)...

A) yup - do that. b) not really much point since there is no requirement for supplementary bonding in a kitchen. There is a requirement for bonding in a bathroom - but that needs to be implemented in (or very close to) the room itself. (you also don't need an explicit connection back to the main earth terminal for supplementary bonding).
More on that here:
http://wiki.diyfaq.org.uk/index.php?title κrthing_and_Bonding
As the cabinet flex has an earth wire (or CPC (Circuit Protective Conductor) if you want to get posh), then this can be used for purposes of both earthing and equipotential bonding. So if its connected to the earth of the circuit that is supplying it, and that earth is also connected to the earth of any other circuits feeding the bathroom, plus any other metal systems that would be capable of introducing a "potential" into the bathroom, then everything that needs doing there has been done.
My guesses from what you have posted here and in other posts:
1) The cabinet is probably working fine. Its transformer is double insulated and can probably be forgotten for the purposed of this investigation.
2) The tingle is getting to the cabinet *from* its connection to the house earth. The fact that you can sense it only when making connection to both the tap and the cabinet suggests that the equipotential bonding in the bathroom is suspect.
3) Your Tumble Drier and Washing Machine will both have mains filters on the inputs. These will tend to try and float their input earth wire connection at half mains potential[1] unless they are properly earthed.
[1] Although the earth is only connected by very small capacitors in the filters - hence the tingle ought not be dangerous since you will not be able to draw any current of significance via this route - but if not tied to a good earth you will feel it.

You may have a poor earth connection to the house. You may have poor earth continuity between the TD/WM socket and the CU.
Did you actually measure this with a resistance range on the DMM rather than just the continuity bleeper range (the latter will bleep on any resistance less than the bleep threshold - and this is often tens or even a couple of hundred ohms)? You want a fairly accurate measurement of the resistance between socket earth terminal and main earth point at the CU taken with the DMM set to its lowest ohms range. The result should be well under one ohm.

Chances are its fine - but don't always assume that as it came from the factory will work! I bought a new CU once that would have shorted the main supply had it been connected in the as supplied state!

--
Cheers,

John.

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On 15/05/2011 12:38, deano wrote:

It doesn't seem to work with threading at all. There are now 12 different threads all with the same subject line! Looks like it creates a new thread every time you post.
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David in Normandy. snipped-for-privacy@yahoo.fr
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On 14/05/2011 12:52, Dave Plowman (News) wrote:

We still need an answer to the question of whether the cabinet is marked with a double insulated logo. Of even a note of if it even has an earth wire connection.
Chances are for a specifically designed bathroom cabinet it will have a two wire feed, and a double insulated transformer for the lights. The case of which will be non conductive. Hence any mains coupling to the case would be capacitive (but not via a "capacitor" as such).
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Cheers,

John.

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On 14/05/2011 12:18, deano wrote:

bare feet on the tiled floor, it doesn't happen with shoes on, just touching the cabinet.

You might want to verify if there is continuity (i.e. stick DMM on a low ohms range) between the tap and main earth terminal before using it as a "known" ground reference.

It would suggest any mains connection is a very high impedance one - i.e. the moment you try to draw even a tiny current, the voltage falls away. This would be consistent with a lump of metal that is capacitively coupled to mains just by virtue of being in close proximity to a mains wire.

If you had a hard connection to mains on the cabinet, then the reading between that and the main earth terminal would have given a very solid ~240V reading.
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Cheers,

John.

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Andy Wade wrote:

Thanks for that.
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Kev

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Ret. wrote:

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.
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Tim Watts

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Tim Watts wrote:

In fact, we haven't had to use the 'compatible' charger for a couple of months because I bought my wife an iPad and that came with an Apple charger that also charges her iPod.
I kept the compatible charger as a 'spare' but, in view of what you say, I'll consign it to the bin.
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Kev



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Ret. wrote:

Wise, for the small amount they cost.
If it were me, I'd stick my Megger across it (ie short all the inputs, short all the outputs then across the pair) on the 500V setting. If it survived that with a high enough reading (say at least 10Megohms) , I'd be happy again.
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On Thu, 12 May 2011 00:26:55 -0700 (PDT), deano
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.
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On 12/05/2011 10:10, Geo wrote:

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.
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Andy

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On 12/05/2011 08:26, deano wrote:

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:
http://wiki.diyfaq.org.uk/index.php?title=Electrical_Glossary

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.
--
Cheers,

John.

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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.
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On 12/05/2011 08:26, deano wrote:

Low Voltage Halogen? Probably an electronic 'transformer' is in circuit, the design of which has some leakage issues particulary near the inlet power filter. Disasemble and snap a picture of it?
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Adrian C


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