Electrode Seperation

[marcuswareham]

Hello

I am wondering what would be the correct method for testing electrode separation distance

For example, if installing an EV charger or hot tub from a PME supply and chosing to TT the EV charger / hot tub, how could you ensure you are a sufficient distance away from any buried PME bonded metal work and therefor making to point of changing to TT pointless. Other than by inquiry or digging up the whole site is there a better way to test for this.

Also if installing an earth rod to pull down the touch voltage of a PEN fault, and bonding it to the PME MET, if you put a ROD down and get a very low loop impedance this could be due to the fact it is close to an existing PME electrode or PME bonded metalwork, so if a PEN fault did occur the loop impedance would be a lot higher than expected. I guess in this case a ground resistance test is needed?

Thanks Marcus

 

[Pete999]

Hello

I am wondering what would be the correct method for testing electrode separation distance

For example, if installing an EV charger or hot tub from a PME supply and chosing to TT the EV charger / hot tub, how could you ensure you are a sufficient distance away from any buried PME bonded metal work and therefor making to point of changing to TT pointless. Other than by inquiry or digging up the whole site is there a better way to test for this.

Also if installing an earth rod to pull down the touch voltage of a PEN fault, and bonding it to the PME MET, if you put a ROD down and get a very low loop impedance this could be due to the fact it is close to an existing PME electrode or PME bonded metalwork, so if a PEN fault did occur the loop impedance would be a lot higher than expected. I guess in this case a ground resistance test is needed?

Thanks Marcus

YouTube earth electrode testing may help you Marcus.

 

[marcuswareham]

YouTube earth electrode testing may help you Marcus.

I have done so, have watched the JW videos on it and some others, and I already understood how to test electrodes.

But still unsure how to test if you are in the PME influence area so to speak, if not known you could be a few meters away from a PME bonded water pipe, etc
In which case if there was a PEN/CNE conductor fault a voltage could occur on your new electrode

 

[pc1966]

Off hand I would say you should first measure the earth electrode independently using the fall-of-potential method or similar, then do a Zs test from the PME supply using your rod a E to get both the supply L-N impedance (i.e. the PSSC value) and the L-E impedance (i.e. the PFC).

Almost certainly the supply impedance will be very low compared to your rod so you can discount it, otherwise take half the supply impedance as 'L' (assuming R1 & R2 are similar) and subtract that from Zs to get Ra. If both methods give comparable earth rod impedances then it is not near the PME earth electrode.

If it was close the supply Zs would be a lot lower due to the short distance.

 

[davesparks]

I have done so, have watched the JW videos on it and some others, and I already understood how to test electrodes.

But still unsure how to test if you are in the PME influence area so to speak, if not known you could be a few meters away from a PME bonded water pipe, etc
In which case if there was a PEN/CNE conductor fault a voltage could occur on your new electrode

If you understand how to test electrodes then doesn't that answer your question?
The presence of other metalwork in the ground should have minimal effect on an earth electrode test (unless maybe if your electrode and your test electrodes are near to and directly parallel with a buried metal pipe, in which case you'll probably get some suspicious test results anyway to alert you to this)

 

[marcuswareham]

If you understand how to test electrodes then doesn't that answer your question?
The presence of other metalwork in the ground should have minimal effect on an earth electrode test (unless maybe if your electrode and your test electrodes are near to and directly parallel with a buried metal pipe, in which case you'll probably get some suspicious test results anyway to alert you to this)

Not quite:

If you were to put a 2m earth rod at the edge of a garden and just the other side of the fence to next door garden there is an underground metal water pipe 1m away from the rod and the pipe was bonded to PME earth

If using a 3 wire test, I cant see how you would detect the presents of this pipe as you would be doing the test in the garden with the earth rod, not the next door neighbours garden which is the direction of the buried water pipe

If doing a loop impedance test (Ze) on the earth rod you might get a very low reading due to the fact that it is so close to the metal water pipe. Hence if there was a PEN fault the earth rod would also have a voltage on

If you did both tests I guess you would see an anomaly in the measurements, which could indicate the earth rod is 2 close to PME metal work, but if only doing one of the tests (sometimes not possible to do 3 wire test due to space restraints) I am not sure how you would know this?

 

[davesparks]

Not quite:

If you were to put a 2m earth rod at the edge of a garden and just the other side of the fence to next door garden there is an underground metal water pipe 1m away from the rod and the pipe was bonded to PME earth

If using a 3 wire test, I cant see how you would detect the presents of this pipe as you would be doing the test in the garden with the earth rod, not the next door neighbours garden which is the direction of the buried water pipe

That's my point, a 3 wire test is unaffected by the presence of the bonded metalwork in the ground.

 

[marcuswareham]

That's my point, a 3 wire test is unaffected by the presence of the bonded metalwork in the ground.

Indeed,

So if installing an earth rod for an EV charger on a small site with a 1x1m garden so no space to perform a 3 wire test so you perform a loop impedance test on it instead, then how would you be able to ascertain if your to close to PME metalwork

 

[pc1966]

So if installing an earth rod for an EV charger on a small site with a 1x1m garden so no space to perform a 3 wire test so you perform a loop impedance test on it instead, then how would you be able to ascertain if your to close to PME metalwork

If your local rod is only for equipment in the immediate vicinity, say several meters, then if the rod get lifted by a nearby PME fault the ground around you will also be lifted to a large degree so the touch potential much less than to "True Earth". Of course if there are long metal fences or similar that true Earth might be closer than you think.

However, if the EV charger uses an earth rod it most likely will disconnect safely unless you are very unlucky and are more or less over the PME's rod.

There comes a point when the risk is low enough and the practicalities of testing for the situation too difficult to justify it.

 

[marcuswareham]

If your local rod is only for equipment in the immediate vicinity, say several meters, then if the rod get lifted by a nearby PME fault the ground around you will also be lifted to a large degree so the touch potential much less than to "True Earth". Of course if there are long metal fences or similar that true Earth might be closer than you think.

However, if the EV charger uses an earth rod it most likely will disconnect safely unless you are very unlucky and are more or less over the PME's rod.

There comes a point when the risk is low enough and the practicalities of testing for the situation too difficult to justify it.

I see, yes some people mention using an earth mat for a hot tub in this case the ground you would be steeping out onto would also raise in potential so the touch voltage would be reduced

I see what you mean about low risk and practicalities of testing, Was wondering as I have seen some videos of EV or hot tub installs where people have just banged in a small electrode TTd the hot tub etc, and just done a loop impedance test on it, without much thought to anything in the ground etc. Which seems to me if they cannot ensure they are far enough from PME then the PEN fault risk is still there and they may as well have just used the PME earth

I was curious about the correct way to test if you are too close, and I guess the answer is to do a 3 wire and a Ze test and compare the results

 

[pc1966]

The other thing is generally the PME rods would be around the route of the supply cable, so probably in the front of houses where the DNO cables tap off from.

 

[marcuswareham]

The other thing is generally the PME rods would be around the route of the supply cable, so probably in the front of houses where the DNO cables tap off from.

yeah if underground, making it even harder for separation , doh

On my road i can see the electrodes at the bottom of the poles so bit easier to tell where they are