Voltage Present on Earth Line

[clanky]

Hello.
Im an enthusiastic diy'er and whilst finishing off a job that a local sparky came to do, i came across this 'fault' that i find a bit worrying.

My house is split up into to two section with separate consumer boards fed from henly blocks. When i was rerouting the earth cables for an additional supply i got a mild belt off one of them. Long and short of it after some testing, i found there was around 75 ish V present on the earth line. I disconnected everything and carried out an insulation test (500vdc) on the supply cable (16mm SWA - around 12m long) and all tested good except even with everything disconnected, i was still seeing 30v on the earth when live.

This is between the earth on that particular supply cable and the main incoming earth. Im presuming that this is an induced voltage? I know that this wasn't strictly safe as i essentially had a live supply with no cpc but i felt i needed to investigate this problem and i was as careful as can be.

Further testing on all the individual circuits from that board showed a few adding (around 8v) to the overall problem but i eventually traced the main culprits to the washing machine (40+v) and a dryer (15V). Is this normal? Obviously with all the earth lines connected this problem doesnt actually exist as any residual voltages would be 'drained' and would therefore be undetectable under normal circumstances so am i creating a problem where one doesnt actually exist? Currently my main concern is that the washing machine, being a cheap indesit, could be on its way out and would best be changed.

 

[johnduffell]

I know that this wasn't strictly safe as i essentially had a live supply with no cpc

I think that's your issue.
A lot of appliances leak to earth as a noise suppression measure, this is normal and wouldn't generally be enough to trip an rcd.
However it's very foolish to break an earth connection on a supply that's not otherwise isolated.
Even the gas guys have huge croco clips to connect across any gas pipes they break into in case of differences between the supplierss earth and the gas pipe/local earth.

 

[Pete999]

Hello.
Im an enthusiastic diy'er and whilst finishing off a job that a local sparky came to do, i came across this 'fault' that i find a bit worrying.

My house is split up into to two section with separate consumer boards fed from henly blocks. When i was rerouting the earth cables for an additional supply i got a mild belt off one of them. Long and short of it after some testing, i found there was around 75 ish V present on the earth line. I disconnected everything and carried out an insulation test (500vdc) on the supply cable (16mm SWA - around 12m long) and all tested good except even with everything disconnected, i was still seeing 30v on the earth when live.

This is between the earth on that particular supply cable and the main incoming earth. Im presuming that this is an induced voltage? I know that this wasn't strictly safe as i essentially had a live supply with no cpc but i felt i needed to investigate this problem and i was as careful as can be.

Further testing on all the individual circuits from that board showed a few adding (around 8v) to the overall problem but i eventually traced the main culprits to the washing machine (40+v) and a dryer (15V). Is this normal? Obviously with all the earth lines connected this problem doesnt actually exist as any residual voltages would be 'drained' and would therefore be undetectable under normal circumstances so am i creating a problem where one doesnt actually exist? Currently my main concern is that the washing machine, being a cheap indesit, could be on its way out and would best be changed.

What readings did you get on your IR tests?

 

[buzzlightyear]

My house is split up into to two section with separate consumer boards fed from henly blocks. When i was rerouting the earth cables for an additional supply i got a mild belt off one of them.

one for those consumers must have been live ,did you not know to isolate the c/u.s before hand .
or did you think ,its ok

 

[JAWS]

Shouldn't you be using Ohms law in his situation

 

[johnduffell]

Shouldn't you be using Ohms law in his situation

Who was that directed at, and in response to which quote?

 

[buzzlightyear]

Im an enthusiastic diy'er and whilst finishing off a job that a local sparky came to do

Shouldn't you be using Ohms law in his situation

read pots 1#

 

[buzzlightyear]

Who was that directed at, and in response to which quote?

think about it .

 

[Pete999]

What readings did you get on your IR tests?

Well you have to ask don't you?

 

[JAWS]

Not you John just in general mate, just thought the Ohms law thingy regarding neutrals using parallel paths as returns.

 

[buzzlightyear]

Well you have to ask don't you?

I was think that me self Pete ,and read the post again.

 

[Pete999]

What were the IR results?

 

[buzzlightyear]

What were the IR results?

now your asking ,any way what were they .

 

[Octopus]

I would be doing basic dead tests ...
.. Not the diy hit and miss.

Why didn't the spark do this?

 

[buzzlightyear]

Why didn't the spark do this?

that is a good question ,maybe he was asking to many questions like us .

 

[Wilko]

Hi - out of interest, what earthing system is used in this installation? In my view, you've had a "near miss" at 75 V, indicating a fault is present. So please get an experienced Electrician with test equipment to review it on site. Otherwise may think you've "fixed it" but just left a hazard.

 

[clanky]

Just back. In answer to a lot of the posts, yes it wasnt probably the wisest thing to break the earth to a live con board but i did.

Insulation test showed pretty much infinity with cable disconnected at both ends.

 

[johnduffell]

I don't agree that 75v measured on a high impedence multimeter is a problem in itself. (Aside from the fact that the earth has been disconnected which is a problem)
50v is the limit of touch voltages of supplies of high current, but 75v that causes a tingle could be 1mA or less.
If it's failing ir tests or tripping an RCD, definitely a danger, but if it's just a low current not dangerous as many appliances leak to earth.
Having said all that, to be clear, none of the above detracts from the fact that the supply should be isolated before removing the earth, and the bonding should really be connected at all times especially on a pme system. Oh, and that the op needs someone competent with suitable test equipment

 

[clanky]

Hi - out of interest, what earthing system is used in this installation? In my view, you've had a "near miss" at 75 V, indicating a fault is present. So please get an experienced Electrician with test equipment to review it on site. Otherwise may think you've "fixed it" but just left a hazard.

As per my first post, the fault is with the washing machine and dryer. Both are now unplugged until i can find a reasonable explanation for their behaviour.

 

[clanky]

I don't agree that 75v measured on a high impedence multimeter is a problem in itself. (Aside from the fact that the earth has been disconnected which is a problem)
50v is the limit of touch voltages of supplies of high current, but 75v that causes a tingle could be 1mA or less.
If it's failing ir tests or tripping an RCD, definitely a danger, but if it's just a low current not dangerous as many appliances leak to earth.

Thanks John, i wondered whether this was normal but the fact that indesit always top the tables on fire hazards had me thinking there may be a fault with the machine. For the record, the circuit is on an RCD and has never tripped.

 

[clanky]

Having said all that, to be clear, none of the above detracts from the fact that the supply should be isolated before removing the earth, and the bonding should really be connected at all times especially on a pme system. Oh, and that the op needs someone competent with suitable test equipment

Point taken and as already mentioned, in hindsight it wasnt my finest hour. But, having found the fault, i investigated it as safely as i could. The earths are all now reconnected before anybody asks. Before i contact my electrician, what tests would you recommend be carried out?

 

[Pete999]

What readings did you get on your IR tests?

I deduct from the 2 optimistic tags I have on this, that you don't think, (like I do) that the OP doesn't have any test gear, with no responses from him it's becoming more and more likely.

 

[buzzlightyear]

Just back. In answer to a lot of the posts, yes it wasnt probably the wisest thing to break the earth to a live con board but i did.

you said it .

 

[buzzlightyear]

rule 1 when removing any Earthing from the met (E.G)bonding
isolate the main switch .

 

[johnduffell]

Before i contact my electrician, what tests would you recommend be carried out?

Would be useful to put a clamp meter on the various cpcs to check the leakage. If you have one.
Other than that you could well be chasing a non issue. There's a reason why it's dangerous to have a missing or broken cpc.

 

[Octopus]

I would start with a Zs at the socket for the washing machine .... maybe its not earthed!

 

[davesparks]

Just back. In answer to a lot of the posts, yes it wasnt probably the wisest thing to break the earth to a live con board but i did.

‘Not the wisest thing’ is a significant understatement, you’ve placed your life and the lives of everyone in the property at risk.

Saying that you are surprised that you measured this voltage after disconnecting the earth of an energised installation is like saying you are surprised that you got wet when you jumped into the ocean.

 

[clanky]

‘Not the wisest thing’ is a significant understatement, you’ve placed your life and the lives of everyone in the property at risk.

Saying that you are surprised that you measured this voltage after disconnecting the earth of an energised installation is like saying you are surprised that you got wet when you jumped into the ocean.

Yeah i get it. Thanks for pointing it out (again) and just to clarify, im not so bloody minded as to place other peoples lives at risk.

Im well aware what i was doing wasnt within the best safety guidelines but moving on, i was rather hoping that i could turn the discussion to the fact i have two appliances that in my opinion are putting excessive leakage voltage onto the cpc. Other than repeating whats already been said, has anybody got anything to add?

 

[Pete999]

A down right rude non response from the OP totally ignored a sensible question regarding IR results, he said he had conducted, makes you wonder sometimes, still he reckons he is sorted, so all's well that ends well I hope.

 

[Pete999]

Yeah i get it. Thanks for pointing it out (again) and just to clarify, im not so bloody minded as to place other peoples lives at risk.

Im well aware what i was doing wasnt within the best safety guidelines but moving on, i was rather hoping that i could turn the discussion to the fact i have two appliances that in my opinion are putting excessive leakage voltage onto the cpc. Other than repeating whats already been said, has anybody got anything to add?

Someone else who has had the profile blocked, what occurring Mods?

 

[clanky]

A down right rude non response from the OP totally ignored a sensible question regarding IR results, he said he had conducted, makes you wonder sometimes, still he reckons he is sorted, so all's well that ends well I hope.

Errr post 17? i have an analogue IR tester so i tend to use it as a comparator rather than define the results in absolute terms. The other reason for the delayed response is as a newbie, all my posts have been subject to approval.

PS Makes you wonder about what?

 

[Octopus]

Before i contact my electrician, what tests would you recommend be carried out?

Hum ........... well... I would start with a Zs test at the sockets that the appliances were plugged into ........ that would tell you if they are earthed and how good the earth loop is ....

the next step(s) depend on the result of the above test.

 

[davesparks]

Im well aware what i was doing wasnt within the best safety guidelines but moving on, i was rather hoping that i could turn the discussion to the fact i have two appliances that in my opinion are putting excessive leakage voltage onto the cpc. Other than repeating whats already been said, has anybody got anything to add?

Why do you say it is excessive leakage voltage? What is the normal voltage on a disconnected cpc for those appliances?
Have you accurately measured the leakage current with the cpc correctly connected?

You can’t introduce a fault (disconnected earth) and expect the installation to perform normally.

 

[plugsandsparks]

Seriously....when you disconnect the earth, you can have any voltage you like up to line voltage. it means nothing, except its about as dangerous as it gets. Try it on a large commercial or industrial installation and sparks will fly. Doesn't mean anything is wrong, in fact it means nothing in the big scheme of things.

 

[Lucien Nunes]

Exactly. OP, your test and the voltage readings you quote are meaningless because you are trying to measure earth leakage, which is approximately a fixed current, using the meter's voltage range. The appliances do not 'leak voltage.' They leak current, which instead of flowing through the earthing conductor of a fraction of an ohm, is being forced to flow through your multimeter set on a voltage range which may have a resistance a milion times higher. So the voltage you read will be a million times what it would be if the earthing was connected up as normal. Suppose the washer leaks 0.75mA, a perfectly normal figure. A meter with an input resistance of 100k ohms will read 75V when inserted into a break in the earthing conductor. Reconnect without the meter leaving say just 0.25 ohms of cable, and you'll get 0.75 × 0.25 = 0.00019V.

Moral: Don't use a voltmeter to measure amps!

 

[clanky]

Exactly. OP, your test and the voltage readings you quote are meaningless because you are trying to measure earth leakage, which is approximately a fixed current, using the meter's voltage range. The appliances do not 'leak voltage.' They leak current, which instead of flowing through the earthing conductor of a fraction of an ohm, is being forced to flow through your multimeter set on a voltage range which may have a resistance a milion times higher. So the voltage you read will be a million times what it would be if the earthing was connected up as normal. Suppose the washer leaks 0.75mA, a perfectly normal figure. A meter with an input resistance of 100k ohms will read 75V when inserted into a break in the earthing conductor. Reconnect without the meter leaving say just 0.25 ohms of cable, and you'll get 0.75 × 0.25 = 0.00019V.

Moral: Don't use a voltmeter to measure amps!

Thankyou. An explanation that makes sense! Appreciate the time you took to write that down. Am i right in thinking this could also be described as an impedance issue with the DVM?

 

[clanky]

Seriously....when you disconnect the earth, you can have any voltage you like up to line voltage. it means nothing, except its about as dangerous as it gets. Try it on a large commercial or industrial installation and sparks will fly. Doesn't mean anything is wrong, in fact it means nothing in the big scheme of things.

Im struggling with this. Admittedly i know nothing of commercial installations but are you saying its 'normal' to have line voltage on an earth line in a correctly performing system? Is the earth line not simply a back up in case of equipment/cable failure?

 

[clanky]

Have you accurately measured the leakage current with the cpc correctly connected?

I thought we'd already established that i hadnt. Hence my question on what is the correct way forward in situations like this.

 

[Lucien Nunes]

re you saying its 'normal' to have line voltage on an earth line in a correctly performing system?

This is not a 'correctly performing' system. It has had its earthing conductor disconnected from earth and now any miniscule bit of leakage is going to show up as a voltage anywhere between zero and 230V. A 'correctly performing' system with its earthing actually connected to earth, will not have this voltage.

If you mean: 'Is it normal to have leakage current flowing into the CPC under normal conditions, that will give rise to a voltage if the CPC is broken' then yes, absolutely normal. All sorts of things cause a small amount of leakage - interference suppression components inside appliances, cable capacitance, normal atmostpheric moisture. The total in a normal installation might be a few milliamps, which is trivial so long as the cable is connected as it should be. Please put it back where it belongs. It is neither necessary, nor permissible, to disconnect it when a system is energised. Faults can be diagnosed without disconnecting it.

One function of the CPC / earth connection is indeed to allow protective devices to operate in the event of a fault. But there are others e.g. collecting the leakage current harmlessly and providing an equipotential between exposed parts. That is why it must remain connected even when no fault is present.

 

[plugsandsparks]

Im struggling with this. Admittedly i know nothing of commercial installations but are you saying its 'normal' to have line voltage on an earth line in a correctly performing system? Is the earth line not simply a back up in case of equipment/cable failure?

No not at all, the earth has a function in nearly all installations. It is normal and necessary to have a direct link between line, 230V and earth. This direct link can be a number of safety devices, like semiconductor type surge suppression, even some products that magically work without a neutral are using the earth, cables have a real capacitance between line and earth and as we have ac voltages, you will pick this up also. There is also other types of leakage due to magnetic effects, they all add up. I know its getting worse because more and more i am having to split an installation down into having multiple RCBOs rather than the standard 2 simply because of accumulated leakage current to earth, largely from electronic equipment. In simple terms and with very sensitive voltage instrument you will see 230V on a disconnected earth, always.

The actual current capability behind it is largely directly proportional to the size of the installation. I have seen earth currents of several amps and one thing is for sure, if i had disconnected it and touched the earth cable it would have really hurt.