Voltage Present on Earth Line

[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.