Voltage on external fittings

SandStone

Hi,

Some of the external screws on light switches, sockets etc. in part of my house seem to have a voltage on them. When I test them with a mains voltage tester, the display lights up with readings of up to 55V. I also get readings on bathroom fittings such as taps. Should I be worried, or is this normal?

davelerave

are you getting a shock, is your house old.if the wiring is old it could be a fault and no neutralizing/bad earthing or could be an esb neutral loose if your house is wired ok

Davy

Has this just started happening? You should use a digital voltmeter to check everything. The max touch voltage should be 50volts. You should get a electrician to check this, and clear your side.

SandStone

I don't get a shock from the fittings that measure 12V and 36V, but I haven't tried touching the 55V one. It's a 1970s house. It's also not consistent around the house, it's mostly around the bathroom. I'm a bit worried about some electrical work that was done there recently, e.g. the light switch works backwards (the off position is on).

Do you mean that the neutral line coming from outside could be loose somewhere outside the house? Is that nothing to worry about?

SandStone

I had never checked it until a few months ago. I have a digital multimeter but I'm not 100% sure how to check this problem with it. Do I put one probe on the fitting I want to check and the other on an earth such as a radiator pipe?

Davy

SandStone wrote: »

I don't get a shock from the fittings that measure 12V and 36V, but I haven't tried touching the 55V one. It's a 1970s house. It's also not consistent around the house, it's mostly around the bathroom. I'm a bit worried about some electrical work that was done there recently, e.g. the light switch works backwards (the off position is on).

Do you mean that the neutral line coming from outside could be loose somewhere outside the house? Is that nothing to worry about?

A lose neutral at the meter is quite serious and esb will take it serious if it is the case. the light switch upside down is not something to be worried about but perhaps if other work was done that might not be up to scratch.

If you call the esb they may get you to get a electrician to check your side of the installation before they come to check.

davelerave

SandStone wrote: »

I don't get a shock from the fittings that measure 12V and 36V, but I haven't tried touching the 55V one. It's a 1970s house. It's also not consistent around the house, it's mostly around the bathroom. I'm a bit worried about some electrical work that was done there recently, e.g. the light switch works backwards (the off position is on).

Do you mean that the neutral line coming from outside could be loose somewhere outside the house? Is that nothing to worry about?

you need to get a sparkie out!.not sure what you're using to test the metalwork .a phase tester is the handiest for checking live metalwork .you can try to turn off the fuses/circuit breakers one at a time and see if you can find one that clears the fault for the time being .if you have to turn them all off together to clear the fault it could be the esb neutral(an esb problem)

SandStone

Thanks to both of you for the advice. I'm using a cheap (around 5 or 10 Euro) mains voltage tester from B&Q. I was under the impression it's more or less a digital phase tester.

KoolKid

Remember if you meter out live to earth you will get an AC reading of 220v
Neutral to earth should read 0

davelerave

SandStone wrote: »

I had never checked it until a few months ago. I have a digital multimeter but I'm not 100% sure how to check this problem with it. Do I put one probe on the fitting I want to check and the other on an earth such as a radiator pipe?

if you say its only part of the house thats affected it may not be the esb .use a simple phase tester on the metalwork ,see if it lights up. you might be able to pull a fuse to clear the voltage for now . if it was the esb you would normally have to pull all the fuses /tripswitches for the voltage to clear.get a sparkie anyhow!

Solair

koolkid wrote: »

Remember if you meter out live to earth you will get an AC reading of 220v
Neutral to earth should read 0

That applies on TN-C earthing systems, known as "neutralised" in ESB terminology. However,it's not necessarily true on TT system (often found in rural areas / older overhead supply areas / older areas of urban areas). There is no local connection between earth and neutral.

You could find that neutral is floating above 0V in reference to local earth. These systems should absolutely never be used to bond pipework or cross-connected with local earth.

We moved into a house which had a TT (not-neutralised) connection and someone didn't seem to understand / realise that this was the case. They had carried out bonding which left pipework live at about 50V as the neutral was completely unsuitable for earth bonding.

Only an ESB engineer can make bonding connections i.e. at a single point before the meter. The rules on this are less strict in other places that use this type of earthing system e.g. the US and UK.

You should contact a registered electrician and have the neutral and earthing system checked out. It may be possible to upgrade the system and have it 'neutralised' if it is TT. However, this is up to the ESB, they may not consider the local supply in your area suitable for TN-C

SandStone

I tested a few points with a multimeter (with one end on my finger) . A light fitting and a screw on a shaver socket gave a reading of 8V (they had registered 36V on the rough scale on my voltage tester). This voltage disappeared when I switched off the trip switch for the light circuit for that area. However, the screw on a nearby socket that measured around 55V with the voltage tester was merely reduced to 12V instead of disappearing altogether. I didn't test this point with the multimeter.

I'm not sure the light switch that works the wrong way around is simply a case of it being upside down. It's a double switch, and the two switches work in the opposite way (and I don't think it's one of those three-way switches used for landing lights etc.). I had a look at the wiring inside, and it looked to my limited knowledge as if there was one wire too many connected.

I don't know whether I have a TN-C or TT system, but I'm in a built-up suburban area.

Davy

SandStone wrote: »

I don't know whether I have a TN-C or TT system, but I'm in a built-up suburban area.

Would be TN-CS then

Solair

Just because you're in a built up surburban area is no guarantee that you're connected to a TN-C supply. While TN-C is preferred and is the usual in urban areas, there are exceptions.

If you look at your ESB meter, you will see the service fuse (usually a black box) just before the meter.

In a TN-C supply, you'll see a Live (Brown or Red), Neutral (Blue or Black) and a very large earth cable (green/yellow stripes) entering this unit.

If there's no evidence of earth wires, it's likely to be a TT system.

TT systems should also have an higher rated RCD or old-style ELCB across the entire installation (or at least SHOULD have!)

Davy

The fact that the Op said

built-up suburban area

its most likely that it is. Should have made it a little more clear

steifanc

we havnt used tt systems in this country in ablut 20 yrs, its all tncs, the electrician makes the connection at the meter , nutralizing the earth , not the esb ,they just service it , spark connects and esb seal, there is no allowed touch voltage to metal , metal should never have any kinda voltage on it ,
stop messing and get a registered spark to test it properly, and the best thing you can do with a phz tester is bin it .

davelerave

Theres still plenty of tt systems about and live metalwork is a common fault in these older systems unlike a good tt system with proper earthing and complete rcd protection .if a customer says the taps are live the first thing i'd do is stick a phase tester on it.the sparkie doing the neutralizing himself is only a fairly recent development

Stoner

steifanc wrote: »

metal should never have any kinda voltage on it ,
...... get a registered spark to test it properly.

+1

To me this sounds like an issue that the forum might not be able to solve, as the thread develops it looks more like a hands on issue IMO.

steifanc

http://www.esb.ie/esbnetworks/downloads/electrical_services_guidebook_dtis_050500_azf.pdf

4. After ESB have completed the connection to the ESB isolator, the Electrical Contractor makes the customer's installation 'live' (by connecting to and closing the isolator
switch), and carries out post connection tests on the customer's installation as specified by the ETCI National Rules for Electrical Installations.

when they say " a safe touch voltage is 50v " they dont mean that 50v is acceptable on any thing connected to the earthing system . they mean 95% of people could be considered to have a body resistance of less than 4,375 ohms at 50V, but at 220V the body resistance falls to about 2,125 ohms for the same grouping. The reason for the fall in body resistance is mainly due to breakdown of skin resistance with rising voltage, the internal body resistance remaining relatively constant for voltages up to about 500V. It is also important to note that the value of 2,125 ohms is an average for the 5% group and that lower body resistances may apply depending on age, gender, climatic conditions, etc.

so in other words 50v under normal conditions is not egnough to kill the average person .


t n c s power transmission is how we in ireland have started to transmit on the delivery side of the grid taking a nutral point from the star in the transformer and nutrlizing the consumers earth at the esb cut out ,
tt earthing systems are very rare in ireland.

steifanc

and if my memory serves me right , there was a case study done where a client complained to a electrical contractor that they were getting what they getting shocks off there sink in the kitchen sinks , the contractor brushed it of to being some sort of static stating somthing like " a touch voltage of 50v is ok " but when the child of the people making the complaint was electrocuted at the sink, the judge rule manslaughter .and the contractor done time!!
some food for taught

knx

I've had a problem similar to this before with a metal hob and the cause was a screw through the cable feeding it. Both these circuits (cooker and lighting) are similar in that they are both fed with just fuses/mcbs and not an RCD. A small short somewhere would not necessarily trip anything out but would cause a problem such as this. You say you had work done recently. You should check if anything has been fixed to the wall directly above or below any electrical fittings and also check behind the problem switch to see if any of the cables have been damaged by the screws holding the switch in place. Having said all that I agree that a qualified sparks is called for.

Davy

steifanc wrote: »

and if my memory serves me right , there was a case study done where a client complained to a electrical contractor that they were getting what they getting shocks off there sink in the kitchen sinks , the contractor brushed it of to being some sort of static stating somthing like " a touch voltage of 50v is ok " but when the child of the people making the complaint was electrocuted at the sink, the judge rule manslaughter .and the contractor done time!!
some food for taught

This is true, was a few years back

davelerave

steifanc wrote: »

http://www.esb.ie/esbnetworks/downloads/electrical_services_guidebook_dtis_050500_azf.pdf

4. After ESB have completed the connection to the ESB isolator, the Electrical Contractor makes the customer's installation 'live' (by connecting to and closing the isolator
switch), and carries out post connection tests on the customer's installation as specified by the ETCI National Rules for Electrical Installations.

when they say " a safe touch voltage is 50v " they dont mean that 50v is acceptable on any thing connected to the earthing system . they mean 95% of people could be considered to have a body resistance of less than 4,375 ohms at 50V, but at 220V the body resistance falls to about 2,125 ohms for the same grouping. The reason for the fall in body resistance is mainly due to breakdown of skin resistance with rising voltage, the internal body resistance remaining relatively constant for voltages up to about 500V. It is also important to note that the value of 2,125 ohms is an average for the 5% group and that lower body resistances may apply depending on age, gender, climatic conditions, etc.

so in other words 50v under normal conditions is not egnough to kill the average person .


t n c s power transmission is how we in ireland have started to transmit on the delivery side of the grid taking a nutral point from the star in the transformer and nutrlizing the consumers earth at the esb cut out ,
tt earthing systems are very rare in ireland.

they're still about(rural ireland here), but most of them have been rewired since and upgraded to tncs.they're a disaster when an earth fault occurs and the earthrod is in bad shape as is often the case,there was no main rcd at the time for these systems either

steifanc

thats who we ended up with voltage operated elcbs in stead of our risuidal rdcs now in use, its unlikey to find a service that isnt using the star point in the traffo.

davelerave

the incidence of neutral inversion in tncs systems with overhead lines would be a lot less now in rural areas .power lines have been upgraded ,20kv lines are commonly in close proximity to houses and connections to transformers are closer and generally good.the tt system was badly implemented years ago .any problems with neutrals ive seen are mostly neutrals at older looped services in towns and long overhead 230 lines.sparkies might not come across much of this in cities

Davy

davelerave wrote: »

the incidence of neutral inversion in tncs systems with overhead lines would be a lot less now in rural areas .power lines have been upgraded ,20kv lines are commonly in close proximity to houses and connections to transformers are closer and generally good.the tt system was badly implemented years ago .any problems with neutrals ive seen are mostly neutrals at older looped services in towns and long overhead 230 lines.sparkies might not come across much of this in cities

Most of the country is still on 10kv, most has been upgraded to 20kv standard but the changeover has not happened on the trafos as of yet in the majority if ireland regardless of urban or rural.

Network map 10/20KV