Short between neutral and earth on supply

Shires

Hi all.

I appear to have a short between neutral and earth on the ESB supply side - measured from the meter.

Long story - people have been getting electric shocks around the house for the last two years. The kind that you'd get off the neutral when it's having a bad day. NOT a full blown belt off the live, the sort that gives you a really good buzz.

Today the plastic casing on a Y-junction on the NTL cable TV feed melted and I heard arcing from time to time. Measured 20v AC difference between shielding from the back of the (earthed) TV and NTL side shielding.

I opened up the distribution board and through a process of elimination found one leak at ~500k ohms internal to the house (since fixed), and a dead short between neutral and earth coming off the feed from the meter and ESB-side ~70 amp fuse.

Am I right in saying the ESB should fix this free of charge? Ever seen something like this?

Thanks!

Rev. BlueJeans

First off anyway, your earth terminal should be bonded to the neutral as is right and proper.

It's called "neutralising", and is done in order to protect any earthed metal by providing a low impedance path back to the grounded side/star point of the transformer so that any protection (fuse, mcb, main fuse, LV circuit fuse) can operate in a timely manner.

The fact that your metalwork/earths are causing shocks is a very serious matter!

Causes include reverse polarity, not necessarily you but one of your neighbours in the same phase, or group.

I would call ESB immediately so that they can diagnose the problem. The on-call NT will assess the situation, or may call back tomorrow to diagnose, but they should make the call to visit you at least.

Have you had work carried out in the last two years?

Are you an urban or rural customer?

You obviously have access to a megger. Do you have an independent earth as well? Use that to measure the voltage on the neutral terminal if you can, and report back. Don't go removing earths, current may be using them as a path back.

Shires

Hey, thanks a lot for the information - much appreciated!

Rev. BlueJeans wrote: »

First off anyway, your earth terminal should be bonded to the neutral as is right and proper.

It's called "neutralising", and is done in order to protect any earthed metal by providing a low impedance path back to the grounded side/star point of the transformer so that any protection (fuse, mcb, main fuse, LV circuit fuse) can operate in a timely manner.
The fact that your metalwork/earths are causing shocks is a very serious matter!

Causes include reverse polarity, not necessarily you but one of your neighbours in the same phase, or group.

I would call ESB immediately so that they can diagnose the problem. The on-call NT will assess the situation, or may call back tomorrow to diagnose, but they should make the call to visit you at least.

Will do.

Rev. BlueJeans wrote: »

Have you had work carried out in the last two years?

It has been happening since as we moved in. Have done a bunch of stuff myself around the house, but am confident about what I'm doing when it comes to simple domestic stuff. Admittedly I know squat about the supply side and not much about analog/AC systems in general.

Previous owners rewired the house and fitted a new distribution board with electronic breakers and an RCD. Although messy, by and large it appears to be OK to me, nothing unusual.

Rev. BlueJeans wrote: »

Are you an urban or rural customer?

Urban.

Rev. BlueJeans wrote: »

You obviously have access to a megger. Do you have an independent earth as well? Use that to measure the voltage on the neutral terminal if you can, and report back. Don't go removing earths, current may be using them as a path back.

Yup, there is an independent earth, presumably a rod from what I can see above ground. The ESB-side and independent earth are bridged at the distribution board. There is no measurable difference between earth and neutral - potential and resistance.

Would it be reasonable to disconnect the independent earth and use it to check the polarity of the supply using the multimeter? EDIT: oops, I think this is roughly what you asked me to do.

You mentioned that the neutralization should be a low impedance link.. Do you think I should be measuring this as a dead short with a consumer multimeter?

Thanks!

davelerave

if the installation is 'neutralized' and metalwork is bonded to 'met',there may be a bad contact on supply neutral
is your supply coming in overhead?
If it's not neutralized(older supplies) you may just have an earth fault and a high-impedance fault path assuming everything is bonded to met

Rev. BlueJeans

Sorry, I should have been clearer.

When I say independent earth, I mean a rod you can stick into the ground (not too near the old one) and use that as a reference. If you could verify if there is current flowing back on your earth on one of the large (probably 10sq) cables running into it (your main earth terminal), that would tell a lot.

A poor neutral, as said above is another possibility, but I'd be more inclined to think that someone made a booboo on one side or another of the meter when your new board went in.

As I say, bear in mind that this may not be your installation (ESB meter and connection included) at fault at all, it could be one of your neighbours on the same phase.

Rev. BlueJeans

And yes, the resistance between neutral and the earth should be very low. The neutral terminal is connected directly to an earth ran from your board back to the ESB main fuse unit.

The reason I'm dissuading you from disconnecting one of the earths yourself is firstly, it may not be obvious which is the neutralising lead back, and which is going to your earth rod, and secondly you may well be breaking the load of not only your own, but possibly your neighbour's as well, with an accompanying risk of shock.

2011

As Rev. BlueJeans has correctly pointed out there would often be a deliberate connection between neutral and earth. In Ireland a "TNC" system is used in nearly always used, as shown in the illustration below.

BTW the in the drawing colours are incorrect (live should be brown and neutral should be blue) and the main switch fuse on the consumer side would normally be 63A with an 80A fuse on the ESB side.

Also from the earth bar there should be a 10mm sq. earth cable to the earth rod.



The ESB supply is often from a "concentric type cable" that looks like a co-axe cable in cross section with the live in the centre, and with the neutral/earth as the "screen".

people have been getting electric shocks around the house for the last two years

What are they getting shocks from???

Electricity will always follow the easiest path. If this is through you then you may have an earthing issue and/or a high resistance path on the neutral (on your side or on the ESB side). Either way this is serious and needs to be sorted sooner rather than later.

The kind that you'd get off the neutral when it's having a bad day. NOT a full blown belt off the live, the sort that gives you a really good buzz.

Perhaps it is not a "full blown" type because you are standing on wooden floor boards, or are wearing rubber soled shoes etc. If you were wet (like in a bathroom) and you were touching something that is well earthed (like a radiator) and you then got a shock it may be the last shock you ever get!!

I was on a large project in Dublin and one of the electricians working in the plantroom kept complaining about feeling a strange sensation when connecting cables. What he did not know was that they were live!! The floor he was standing on was covered in pitch (a very good insulator). One day when he was connecting them he leaned against metal trunking. Bang!! He was our of work for a long time after that with severe burns and was very lucky to be alive. Sadly on other projects I worked on some people were not so lucky, they did not survive.

Please dont take this the wrong way Shires I am not trying to offend, but when someone says something like this:

Have done a bunch of stuff myself around the house, but am confident about what I'm doing when it comes to simple domestic stuff.

and then this:

Admittedly I know squat about the supply side and not much about analog/AC systems in general.

and this:

a dead short between neutral and earth coming off the feed from the meter and ESB-side

It shows that you do not know enough to be carrying out this type of work. Remember mains voltage can kill!

This is the next thing that would worry me:

Previous owners rewired the house and fitted a new distribution board with electronic breakers and an RCD. Although messy, by and large it appears to be OK to me, nothing unusual.

If it was recently rewired it should not be "messy". It should look like a proffessional did the work and nobody should be getting any shocks.

OP I think it is time to call in a registered electrical contractor. Best of luck!

Rev. BlueJeans

Bumping this in hope of an update.

Rujib1

Rev. BlueJeans wrote: »

Bumping this in hope of an update.

Bluejeans. You seem to know a bit of stuff:D I have a question, which to date 2 registered contractors have failed to answer.
I have kitchen light on two way switch. If I have a CFL bulb in the fitting, it works fine when it is on. BUT, when I turn it off, it goes off and then about 5 minutes later it flickers on for a half a second, and continues to do so for hours on end. Maybe flickers on once every 2 to 3 minutes just for a milisecond. I have moved the same bulb around the house to other fittings, and I have no problem. I have tried other CFL bulbs in the same fitting, and the problem continues.
I have tried standard light bulbs in they same fitting, but the blow very regularly :mad: Maybe twice a month!!

One other thing, all around the house the lights seem to dim a little (like as in somebody using the electric shower) for 10 to 20 seconds, and then come back up to full power. That may happen once or twicw an hour!

I am rural based. House has had no new stuff wired in in the last 10 or 12 years, and I have seen the issues described above only over the past 2 years or so!

For a while I put down the issue of all the lights losing power to perhaps a neighbour on same transformer using a welder or the likes. Haven checked with him, I have eliminated that possibility.

Had 2 different electricians look at the problem, but to be honest I may as well have asked my dog:eek:

Any thoughts???

Rev. BlueJeans

Your flickering cfl problem seems like a broken neutral to me. It's possible that the two way switching is breaking the neutral rather than the phase, is what I mean, possibly due to crossed wiring at the ceiling rose, or the one before it in the lighting circuit. A CFL will possibly try to fire under such a scenario whereas an incandescent bulb may not.

That's been my experience anyway, and something worth checking.

Your neighbour may not be using a welder, but if there are a few of you on the group, then any load may be a factor, such as a cooker or electric shower. If your lights are on dimmers (just a possibility) then you'll notice the flickering a bit more, as transients in the voltage coming in can cause little variations that you'll notice quite readily. Ask your sparks to do a loop impedance check, it should be quite low, anything over .5ohm at the customer tails, and Networks will pencil you in for further inspection, or what's called an SI (system improvement).

HTH.

2011

It's possible that the two way switching is breaking the neutral rather than the phase, is what I mean, possibly due to crossed wiring at the ceiling rose, or the one before it in the lighting circuit.

Perhaps.

I think that it is caused by capacitors within the CFL discharging. The diagram below shows the components in a typical CFL. If you look at capacitor C4 in the drawing below you will see that it is connected across the output side of the bridge rectifier. When mains power is on C4 will charge up fully, but when mains power is removed it will to dicharge into the circuit.




I think that this discharge is supplying the firing circuit for the lamp (but not enough for it to light fully) and causing the lamp to flicker. Capcitors can hold considerable charge for quite a long time.

Your neighbour may not be using a welder, but if there are a few of you on the group, then any load may be a factor, such as a cooker or electric shower.

Exactly. I have seen this quite a bit in rural areas when the farmer milks in the evening neighbours have similar complaints. I would think that this problem is caused by "external factors". Remember the ESB only promise you an average of 230 volts, this voltage will vary and is permitted to within a tollerance. If you are concerned you can contact ESB Networks and they will hook up a machine that will graph your supply voltage over a number of days to establish that you are within tollerance.

Rev. BlueJeans

Yep, a voltage recorder can be installed for a week, on request. A loop impedance check can be done at the same time, but you'd probably have to ask the NT to do that, as some do and some don't. If it flags an issue needing improvement, then they may split the group and install a new sub (transformer).

I wouldn't put it down to a smoothing cap tho', although I have seen that happen too (with certain brands only-a 3.3uF cap would be small enough), as he says it only seems to be happening in one location, with different lamps, which behave elsewhere. As you know, with the vagaries of wiring, a broken neutral may not always equal no voltage in the circuit

2011

A loop impedance check can be done at the same time, but you'd probably have to ask the NT to do that

Whats an NT Rev??

with the vagaries of wiring, a broken neutral may not always equal no voltage in the circuit

Yeah, you may have a point. Perhaps either the neutral or the live (which ever is being switched) is not 100% off when the switch is in the off position.

Rev. BlueJeans

Oh sorry!

A Network Technician, basically a title that ESB gave their staff when they craft accredited them, rather than seperating them into linesmen and electricians, back in the mid nineties.

Could be a defective switch too, I hadn't thought of that. OP, you could check if it happens from both switches?

2011

NT, thanks!
I must remember that

Rujib1

Rev. BlueJeans wrote: »

Your flickering cfl problem seems like a broken neutral to me. It's possible that the two way switching is breaking the neutral rather than the phase, is what I mean, possibly due to crossed wiring at the ceiling rose, or the one before it in the lighting circuit. A CFL will possibly try to fire under such a scenario whereas an incandescent bulb may not.

That's been my experience anyway, and something worth checking.

Your neighbour may not be using a welder, but if there are a few of you on the group, then any load may be a factor, such as a cooker or electric shower. If your lights are on dimmers (just a possibility) then you'll notice the flickering a bit more, as transients in the voltage coming in can cause little variations that you'll notice quite readily. Ask your sparks to do a loop impedance check, it should be quite low, anything over .5ohm at the customer tails, and Networks will pencil you in for further inspection, or what's called an SI (system improvement).

HTH.

Thanks. I had an inkling myself that the problem may have been related to crossing of live and neutral somewhere in the system. I had thought local sparkies would have been able to do simple test to verify or not. When I suggested as much to them, I got that vacant stare you get from a politician who has just lost his seat.
One of them suggested to me that criss crossing of live and neutral cables in my attic could be the root cause.
Anyway I suspect from what you say that the poblem may be in the ceiling rose directly at the point of flickering light. Think I will try swapping wires here to see if issue goes away.

Thanks

Rev. BlueJeans

It's a long haul, but definitely worth belling out the lighting circuit in question. The dreaded junction boxes may be present, but the important points are that every light is broken through the phase, that the circuit isn't overloaded, and that the earthing is intact (if indeed it's there at all).

Start a thread here if you need any help, there are a couple of us about

One of them suggested to me that criss crossing of live and neutral cables in my attic could be the root cause.

Actually this isn't as far fetched as it might sound, although he was probably bullsh1tting.

I don't wire houses as a rule, but I did one last year for a mate of mine as a moving in present. Did the post installation checks, the works. All was well, bar about 8 or 9 volts on one lighting circuit (quite a large one, switching 6 circuits, mostly two way and intermediate in the landing and stairs area). Tried everything, including earthing the circuit in question (no current flow) and the ultimate cause was my tidy looming of all the cables the length of the house. As I wasn't going tearing the lot out, I decided to live with this induced voltage, and the only manifestation has been a very very faint glow in the LED lights in the skirting and stairwells, when off, of course.

Every installation is different!

Shires

Thanks all for all the pointers - they gave me an "in" with Google and led the way to some very interesting reading!

Rev. BlueJeans wrote: »

Bumping this in hope of an update.

Sorry for not replying earlier - things have been developing.

With an independent earth rod in the back garden and load on the supply there was a 4-5v differential. It confirms (to me anyway) that the earlier 20v diff I was seeing on the cable TV shielding is a problem with the supply to the house. The cabling between the ESB meter and internal distribution board had very low impedance (measured by an ESB NT - thank you sir!), so that is (probably) OK.

Mrs. Shires just rang to tell me that the ESB have found a problematic cable outside - she doesn't know which one, I asked her to find out.

I saw the voltage differential on the NTL cable feed before when the house had no significant load whatsoever, so my uneducated feeble guess would be that it's not the cable from the ESB's break-out point to the house (what are these called?), but something further down the chain. I'm very interested to find out.

Oh, one other symptom we had was a slight 50Hz audio hum on one TV upstairs. My best guess at the time was it being due to induction on the RF cable but could not isolate a cause for that. I will be delighted if it solves that issue too.

2011 wrote: »

As Rev. BlueJeans has correctly pointed out there would often be a deliberate connection between neutral and earth. In Ireland a "TNC" system is used in nearly always used, as shown in the illustration below.

Ah ha. :pac: I was expecting there to be a separate earth - the two older houses I've worked on to date looked like this, and had ELCBs instead of RCDs. I've since learned these are TT systems. I was expecting my house to be the same (at least with respect to the earth), hence my confusion.

2011 wrote: »

I was on a large project in Dublin and one of the electricians working in the plantroom kept complaining about feeling a strange sensation when connecting cables. What he did not know was that they were live!! The floor he was standing on was covered in pitch (a very good insulator). One day when he was connecting them he leaned against metal trunking. Bang!! He was our of work for a long time after that with severe burns and was very lucky to be alive. Sadly on other projects I worked on some people were not so lucky, they did not survive.

Heard a few horror stories alright. At one former workplace a man before my time was melted from falling against exposed 3 phase bars in a mainframe computer installation. I'm told my Grandfather's heart was in the center of his chest after an accident with a spanner at a hydroelectric power plant.

2011 wrote: »

Please dont take this the wrong way Shires I am not trying to offend, but when someone says ..... It shows that you do not know enough to be carrying out this type of work. Remember mains voltage can kill!

No offense taken.. As a kid my toys were things like oscilloscopes, power supplies, signal generators, odd radios, soldering irons, bread board, nitric acid and PCB etching, massive capacitors (fun!), and boxes and boxes of components - valves, LEDs, 74xx ICs you name it. Never took it any further as an adult.

By 10 I had been electrocuted plenty, and developed a very keen respect for electricity. These days I know enough to not endanger myself - I know that there are things I don't know - hence my questions here because I did not understand what I was seeing.. To rely on guesswork and patchy knowledge alone is the fast path to failure!

Thank you everyone for the help!

Rev. BlueJeans

4 to 5v discrepancy sounds like a neutral inversion (just a guess mind you). IOW, a phase may be earthed somewhere on the group, which may be your problematic cable. Anything over two volts, and ESB will be digging, possibly literally.

The hum on the TV upstairs is probably whats called "caption buzz". This is when the rf alignment on the tuner is slightly out, and the vision sync pulses (50hz) are heard through the audio, often when captions are present on screen.

I don't know much about NTL, but the cable may be carrying dc to feed distribution amps etc., along the way.

Davy

Shires wrote: »

so my uneducated feeble guess would be that it's not the cable from the ESB's break-out point to the house (what are these called?), but something further down the chain. I'm very interested to find out.

Break out point? Do you mean the little pillar/box outside where the other end of all the service cables goes, or the hole their digging now?

Rev. BlueJeans

I assume he means the service cable from the minipillar to the house, which is most likely fine.

Actually, thinking about it, the fact that he's in an urban area makes the possibility of a neutral inversion remote.

I'm sure the esb lads were scratching their heads too, a fault of this nature can be hard to diagnose, and urban substation earths are notorious for picking up induced voltages along the way.

Davy

Ye thats what i was assuming alrite, but OP have none of the neighbours noticed a problem since problem seems to be the mains? Actually guess it doesnt really matter if they have found the fault, they must be in the process of repairing it

Dotsie~tmp

As said previously there is supposed to be a short between earth and neutral at the supply. From the ESB cutout backward hey are the same conductor! The PEN.

Do you have a lot of carpeting if the house? Some people are prone to static shocks. I often get a little zap off my TV supply too BTW.

emmiou

The NTs were out and had a look at all the cables - they have replaced the connections between the electricty cables at the pole and the subjunction box that serves our group of houses. The neutral was carrying a 1.6 amp charge when the electricity in our house was turned off at the fusebox, this increased when the electricity was switched back on and some appliances were turned on. The said to see how we get on with this.

Rev. BlueJeans

Interesting. You'd expect current flow in the neutral with appliances on alright, but assuming that all houses were off, then obviously there should be no flow there.

Let us know how it goes anyway.

sparktest

Folks - clear something up for me, you said earlier that the ESB connects neutral connected to earth to give us a TNC system... However this then splits out into E and N bars in the MCB box so shouldn't our system be TN-C-S. N and E first combined then separate??

Thanks.

Rev. BlueJeans

You're quite right. The system in question is TNC-S (Terra[earth] Neutralised, Combined, and seperate).

evosteo

hi lads listen i was just looking a a shower for a friend tonight. they have been having trouble with it for the last 3 monts now. the problem is the hot water supply. its a mira 9.5kw 240/230 electric shower supplied with a 6 sq t+e, water pressure is fine and is barely a year old. whats happening is when the shower is turned on it might give hot water for 5 - 10 seconds then only cold water. iv done the following things, checked the element and wiring continuity,micro sw and stat and all are working correctly. what i did find is that the voltage at the shower is only 209 volts. i went to the board to check the voltage and only got about 210 max incoming.

the only conclusion i can come to is that the shower isnt functioning correctly on 210v.

has anybody had an issue like this before?

its a first if so for me. i told them to get in touch with the esb to see if they can boost the voltage to the house

also they replaced their old shower with this new 1 BECAUSE of a similar problem they had with it.

any suggestions?????? they would all be welcomed

meercat

Check the shower head to see if there is a build up of calcium blocking the nozzles.Also 10 square cable would prevent volt drop even though supply voltage is low.

Rev. BlueJeans

This should really be on its own thread, but anyway;

If the voltage is 210 under load, what is it with the shower off?

While it's within tolerance, it's on the low side, that said a drop to 210 isn't going to stop the heater element from working altogether

If there's an issue with the load, contact ESB networks and they will install a voltage recorder to analyse the supply over a week or so.

evosteo

shower head is grand no bulid up and the voltage at the shower is 208-209 and measured at the board is 210 so i dont think there is a significant volt drop as the run is roughly 10 meters, and i agree that the cable should have been a 10sq though but i still fell that this is a voltage supply problem as in the esb are only supplying a maximum of 210 volts. although on there website its states that it coul go as low as 207 which seems rediculous to me for equipment rated at 230-240 volt


also the voltage reads 210 at the board when the shower is either on or off and the same at the shower.

im goin to email mira now to see if their equipment would work on a 210v supply