Voltage Present on Earth Line

[davesparks]

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

The established correct way forward for situations where the earth of a live installation is disconnected or missing is to connect it ASAP, ideally isolating the installation until it is connected.
For a situation where an out of the ordinary earth leakage is suspected then the way forward is probably to measure it first of all.

 

[clanky]

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.

Ok, this makes some sense. In my world the increasing use of cheap chinese SMPS's, especially in computer equipment, is definitely having an effect on inherent noise quality. That plus the use of crap zenor's (maybe the semi-conductors youre talking about?) as an after thought doesnt really address the initial problem in the first place. I could bemoan the loss of a good heavy linear PSU but then we all luv' a bargain dont we?

Im still surprised that there could be 240v on the earth line though. I guess everyday is a school day.

 

[clanky]

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.

Exactly that. I neither expected or was aware that such a state could exist.
But, im still surprised at the extent that the earth line is used. Especially in my case where the machine is at standby. Had the motor been running i could sort of, maybe have justified it in my head.

 

[clanky]

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.

System was put back to normal as soon as i diagnosed the problem and in the interests of safety (and curiosity), ive now ordered a current meter. Im still uncomfortable using the washing machine and the meter was cheaper than replacing it. Although that might still happen if my OCD wins the day.

Again, ive learnt something and perhaps now appreciate the more puritanical postings earlier in this thread.

 

[clanky]

Im working my way through this in order to understand the situation a bit better. Link may help others who are as ignorant as i

The principles of Protective Multiple Earthing (PME) - https://www.voltimum.co.uk/articles/principles-protective-multiple-earthing

 

[johnduffell]

Im still surprised that there could be 240v on the earth line though.

I think that's your problem here, the misunderstanding of v=ir. Where for AC there r could actually be impedence.
If you have a 50kO resistor connected to line and the cpc, you will get a small current 5ma and nothing will go wrong
Disconnect the cpc and you will get 0v across the resistor due to no current flowing v=0mA*50kO therefore 240v to earth on either side, but very little shock. If you touch it a small current a few Mili Amps will flow and the voltage will be 150v or so and you'll feel a tingle.

 

[Octopus]

I think whats missing here is application of basic dead tests

"seeing" 75 v on the CPC could simply mean the CPC is not continuous back to the fuseboard.

 

[johnduffell]

I think whats missing here is application of basic dead tests

"seeing" 75 v on the CPC could simply mean the CPC is not continuous back to the fuseboard.

I think he knew that (as he disconnected it). I think the problem was he doesn't understand why and whether it's a problem in itself.
Although you reminded me that you could test between all conductors and get 0v but you should really dead test to any bonded or earthed metalwork in the area as well.

 

[w0z]

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?

It's certainly not a Dvm "issue", A Dvm has input impedance as does an analogue vm. By asking that question it appears that you still have no appreciation of what you're actually measuring, and I suppose by inference.. (I'm too polite to finish that sentence).. It is however a "you performed a dangerous/stupid test" issue

 

[w0z]

I think that's your problem here, the misunderstanding of v=ir. Where for AC there r could actually be impedence.
If you have a 50kO resistor connected to line and the cpc, you will get a small current 5ma and nothing will go wrong
Disconnect the cpc and you will get 0v across the resistor due to no current flowing v=0mA*50kO therefore 240v to earth on either side, but very little shock. If you touch it a small current a few Mili Amps will flow and the voltage will be 150v or so and you'll feel a tingle.

That depends which end of the resistor you touch...