finding an electrical fault

Page 1 of 2  
After doing some electrical work I now get a mild shock when using the bathroom tap. It's a TT system. I have a couple of questions.
1. Am I looking for a live/earth fault only.
2. What's the best way of checking the taps etc. to see if the fault persists after I find the fault(s).
3. The RCD didn't trip since I was working on lighting circuits. What can I fit to my consumer unit to prevent/alert me to such faults in the future.
Thank you, Neil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

future.
If it's only a mild shock, it sounds as if live is connected to the tap through a high resistance (e.g. brickwork) and that the tap isn't properly earthed.
Have you measured the (ac) potential between the tap and a proper earth? If so, re-do this after you have fixed the fault, and it should be zero.
I had a problem a few years ago where a builder had screwed into a live wire when fitting a skirting board - making the whole wall slightly live. This only came to light when we were wallpapering the wall - because the dampness of the paste made the wall conductive, and we were getting tingles off it. Maybe your problem is similar?
Roger
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's not a safe assumption -- it might be that Niel was not well earthed, and if he was, then a full mains belt is readily available.
This situation is not something to treat lightly -- the potential for a fatality might already be there. If you are not fully familiar with electrical fault finding and you have a problem of this nature, I would suggest getting an electrician in and keep well away from any areas you have found with this problem until it's been fixed.
This reminds me of the chap electrocuted in his bath a few weeks ago when the showhead fell into the water.
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks for all the replies. Went back over the work I did and found a neutral switch wire, in the switch itself, had come loose. Should this be live though?
Neil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

can
When the bulb becomes live the neutral will have touched to earth through the broken/loose conductor and enough current would flow in it to give the symptoms you described.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I don't think the light was switched on when I recieved the shock. Neil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

the
fault
What
tap
would
you
be
the
It might have to be on, it only needs other circuits in the house to be used, to create the back feeding effect along that broken/loose conductor and give the tingle.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Just a few questions to start. Is your consumer unit a spilt board with sockets, cooker, shower RCD protected and the other ccts non RCD protected. When working on your lights even with the lighting mcb off did your rcd trip when you touched the neutral to any other bare wires Are your water and gas pipes earthed from your earth block in cu where they enter your property ? And do you know if any plastic fittings ( elbows t pieces etc ) have been added to your copper ?installation at any time ?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Everything except lights are RCD protected.

Didn't try this.
Are your water and gas

Yes
And

Yes, but I have added supp bonding to accomodate this.
Thank you, Neil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Niel A. Farrow" wrote in message

Firstly, seeing that you're posting via caltech.edu, can you confirm that you're in the UK?
Secondly (assuming that you are in the UK) it's most unusual and potentially VERY DANGEROUS to have non-RCD protected circuits in a domestic TT installation (or ELCB protected in the case of older installations). It's not actually banned by BS 7671, but in the event of an earth fault on a lighting circuit you're relying on having sufficient current flow to earth to blow the fuse or trip the MCB. This means that your earth electrode resistance has to be very low indeed, requiring an extensive earth system. Referring to Table 2D in the OSG you'll see that the measured earth fault loop impedance for a circuit protected by a 6A Type B MCB must be 6.4 ohms or less. Given that the external (supplier's) component of this, Ze, is allowed to be as high as 21 ohms you can see the problem! Even with a typically low suppliers Ze of an ohm or two, your earth system would need to be under about 4 ohms, and you will not achieve this with the two rods that you mentioned in another thread.
I conclude that your installation may be inadequately protected and therefore very dangerous. Whoever has caused the installation to be like this, by modification or whatever, is seriously negligent in a way that makes me think that Part P might be a good idea after all. The 'quickest fix' would be the insertion of a 100 mA Type S (time delayed) RCD in a separate enclosure in the meter tails, between the meter and exisiting consumer unit.
There isn't sufficient information to diagnose the fault symptoms that you described, but _one_possibility_ is that in modifying the lighting circuit you've introduced a phase-earth fault (e.g. trapped a wire and nicked its insulation in a junction box) which is not being cleared due to the lack of RCD protection combined with the earth fault loop impedance being too high to operate the overcurrent device. Such a fault would make all your 'earths' live (and your earth rods hot, and your electricity bill ...). If you have neighbours who are also using TT earthing then its possible for the fault described to make their earths live too, via connection through bonded metal water pipes.
This needs sorting urgently. A simple test to start with would be to isolate the lighting circuit in question (pull fuse or turn off MCB) and see if the shocks from the tap stop.
--
Andy



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

First it might be an electrostatic shock, in which case no worry. But if it isn't:
1. it is likely to be life threatening 2. its the result of multiple faults, not just one 3. it needs sorting very quickly. 4. it only takes one bath to kill.

this wont fix it actually, the pipework would still be unearthed, the earth leakage still present, and the level of RCD protection inadequate to protect against this fault.
Regards, NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"N. Thornton" wrote in message

How do you know the pipework is "unearthed" (what ever that might mean)? The OP mentioned having added supplementary bonding.

Have you got the faintest clue what you're talking about? We know that the OP has an earthing system consisting of two earth rods. What grounds do you have for thinking that the earth electrode resistance is greater than the 500 ohm upper limit required to provide adequate protection against indirect contact when a 100mA RCD is in use? The chances are that it will be less than the 200 ohm guideline figure in the OSG, which includes a large factor of safety. The RCD will trip well within the permitted disconnection time (5 seconds in this case, since we're considering a fixed equipment circuit).
Actually there _might_ be a simpler way to add RCD protection to the lighting circuit(s) in question and that's to change the MCB(s) in the existing consumer unit - if it is an MCB type, that is - to RCBO(s), space permitting.
--
Andy



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Unfortunately there is no room for RCBOs, unless they have started making thin ones. Thanks, Neil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
     snipped-for-privacy@alumni.caltech.edu (Niel A. Farrow) writes:

Single width ones are available for many (if not all) makes of CU.
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I guess you and I are thinking of 2 different scenarios, either of which could be true. We know the OP has earth rod/s, and we know he's getting zapped off the bathroom piping.
Option 1: there is no RCD/ELCB protection on some of wiring - that would surprise me, as its a no-no with local earth rods, and has been for quite a long time.
Option 2: the pipework isnt earthed.

I think so. Both the above look like viable options from the info I've got so far. And even if they weren't due to some oversight, I think I'd still have [at least] a faint clue what I'm talkin bout.
That comment is correct for the option of the pipework being unearthed, but not if its earthed but no RCD/ELCB in circuit.

I'm not saying that. Whichever scenario is correct, fitting a whole system RCD isn't going to solve the problem.

That would be rather better, tho again it wont be a solution. The only solution is to a) fix the earth leakage problem b) fix the RCD protection
Regards, NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"N. Thornton" wrote in message

We also know that the shocks started when Neil made alterations to a lighting circuit which he has told us is not RCD protected.

It shouldn't surprise you because he has told us that there is no RCD protection on the lights. Yes, that's a "no-no" - that's whole point!

Can I remind you that this pipework doesn't need to be earthed. There has to be main bonding to incoming services, and local supplementary bonding in bathrooms. The latter may quite legitimately end up being electrically floating if there is plastic piping involved and no link back to the main earth terminal (as would happen if the local bonding only involved extraneous-conductive-parts).

Well, of those options, No. 1 is not in itself a reason for shocks, but it would allow all his earthing to sit at (almost) full mains voltage indefinitely if an earth fault were to occur on the non-RCD protected circuit. That the latter had occurred was my supposition. Again, option No. 2 is not a reason for shocks from taps - although a lack of local supplementary bonding combined with some other fault might be, but I don't think that's relevant in this case.

Which comment? You've lost me.

Now I have to disagree. I think that the problem is an earth fault (or a light wired between phase and earth, or something like that) which is not being cleared because there's no RCD on this circuit and Zs isn't low enough to cause enough current to flow to trip the MCB. Therefore his earthing is live, therefore his taps are 'tingly' - the shocks are from current flowing to earth via body capacitance. If the local bonding is doing its job it will prevent a really serious or lethal shock.
The lighting circuit(s) need to have RCD protection added. A "whole system RCD" as you call it is one valid option, and it needs to be a 100mA Type S one in order (a) to avoid nuisance tripping of the lights and (b) to permit discriminative operation of the other (30mA, fast) one downstream.

Yes, I was taking that as read.

Precisely - that's what I said in the first place :-)
--
Andy



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi
Well Andy, I disagree on a number of the details you brought up, but the OP should first sort out the earth leakage fault, and ensure all circuits are RCD protected. That's the real point.
Regards, NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

About the earth bonding. I think that this will not reduce a shock, but only reduce it to an acceptable (less than 50V) level. In fact, if I hadn't put supp bonding in the bath then I wouldn't have been shocked. The loose wire touching the light box must have caused a current too the earth bar of the CU and hence through the earth and supp bond system. Neil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Option 3, there is an electric fence system with an earth common with the mains earth (yes I know it's against regulations). I suffered from this until I realised the error of my ways and separated the electric fence earth. It gave me several quite noticeable shocks of the pipework under the sink one day when I was working there.
--
Chris Green ( snipped-for-privacy@x-1.net)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You may find that the taps are earthed, and you were charged up. i.e. wearing trainers, walking over nylon carpets etc.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.