Earth in a shed

Wearb

I was servicing a boiler in a shed yesterday and noticed no continuity between L and boiler casing. While sorting this I noticed that the power from the consumer unit in the house to the shed was just 2 core and the shed earth taken from an earth rod at the back of the shed. Everything seems fine but I am left wondering if this is an acceptable way to do it?

10-10-20

You mean "E and boiler casing"?
So no earth in the feed to the boiler, but there was an earth attached to the earth terminal which came from a local earth-point.
Was there an aux panel with RCD's in the shed, or was the boiler alone in having power in the shed?

2011

Wearb wrote: »

I was servicing a boiler in a shed yesterday and noticed no continuity between L and boiler casing. While sorting this I noticed that the power from the consumer unit in the house to the shed was just 2 core and the shed earth taken from an earth rod at the back of the shed. Everything seems fine but I am left wondering if this is an acceptable way to do it?

This arrangement is not acceptable. For a start the earth fault loop impedance would be very high even with the local earth rod. There should be a 3 core cable (L, N & E) from the main board to the shed.

Wearb

I got the earth sorted out. It was a corroded tag on the casing, probably caused by a slight condensate leak. I moved this connection to a dryer part of the boiler and fixed the leak. I suspect that the earth might even have worked under load but not show on a multimeter.

The shed has its own RCD and MCB's.

However it is the apparent disconnect between the house earth and the shed earth that I am concerned about. I know it's all the same earth in the long run, but just wondering if I should have written it up on service report as a potential fault. (I didn't as I didn't want to needlessly (perhaps) worry the old pair)

2011

Wearb wrote: »

I suspect that the earth might even have worked under load but not show on a multimeter.

Define "worked"

I would expect the earth fault loop impedance to be far too high. This will result in protective devices taking too long to trip or not tripping at all.

However it is the apparent disconnect between the house earth and the shed earth that I am concerned about.

As you should be. I would use a "wander lead" to measure the resistance between the shed earth and the MET in the main board. This will tell a lot.

I know it's all the same earth in the long run, but just wondering if I should have written it up on service report as a potential fault. (I didn't as I didn't want to needlessly (perhaps) worry the old pair)

What you have to consider is that it is a very poor connection to the "same earth" at the shed. An earth rod would typically provide a connection with a resistance of 100 to 200 ohms to earth.

Wearb

2011 wrote: »

Define "worked"

Point taken. I just meant that that it might have tripped the RCD under most common fault conditions.

I would expect the earth fault loop impedance to be far too high. This will result in protective devices taking too long to trip or not tripping at all.

As you should be. I would use a "wander lead" to measure the resistance between the shed earth and the MET in the main board. This will tell a lot.

Beyond my pay grade

What you have to consider is that it is a very poor connection to the "same earth" at the shed. An earth rod would typically provide a connection with a resistance of 100 to 200 ohms to earth.

Should I inform the householder. From a personal professional point of view i am probably covered as i would not be expected to investigate beyond establishing the earth presence with a multimeter.

.

2011

Remember RCDs wonderful and all as they are only provide supplementary protection, therefore they should be treated accordingly.

Yes, I would inform the home owner. The wiring is not compliant with the rules.
It would be best to get a REC to resolve this issue.

Wearb

2011 wrote: »

Remember RCDs wonderful and all as they are only provide supplementary protection, therefore they should be treated accordingly.

Yes, I would inform the home owner. The wiring is not compliant with the rules.
It would be best to get a REC to resolve this issue.

Thanks. I will do that.

Michelinextra.

This would be common enough in the UK but not here

Maybe it was an English spark that did the work

Michelinextra.

Wearb

I don't know who wired it. Rural house and looks about 30 years old. Shed, maybe newer.

2011

Michelinextra. wrote: »

This would be common enough in the UK but not here

This is not what is shown in the diagram you posted.

In fact this diagram shows what is often done in Ireland i.e. a sub distribution board fed from the main board with a 3 cores providing a phase, neutral and earth.

Edit: my bad. I just saw the note on the drawing explaining that the earth does not link both boards.
I’m not a fan of this arrangement to be honest.

Michelinextra.

2011 wrote: »

This is not what is shown in the diagram you posted.

In fact this diagram shows what is often done in Ireland i.e. a sub distribution board fed from the main board with a 3 cores providing a phase, neutral and earth.

Edit: my bad. I just saw the note on the drawing explaining that the earth does not link both boards.
I’m not a fan of this arrangement to be honest.

Me neither

Michelinextra.

https://professional-electrician.com/technical/stroma-certification-supply-chain/

A bit of a read-up on it there

Not sure why they did it here unless there was no neutralising present and they decided to do it

In that case they should have dealt with the neutralizing as part of the work

stickman1019

Essentially in this diagram they are converting the TNCS to an IT system locally.


This is the same arrangement allowed for in Electric Vehicle charging points in BS7671.


Think the school of thought boils down to not relying on the PEN when cabling is exiting a building.


There is a lot on info on youtube on this including the Amendment 1


The Amendment is available from the IET website on the below link for viewing


https://electrical.theiet.org/bs-7671/updates-to-18th-edition/

Michelinextra.

stickman1019 wrote: »

Essentially in this diagram they are converting the TNCS to an IT system locally.


This is the same arrangement allowed for in Electric Vehicle charging points in BS7671.


Think the school of thought boils down to not relying on the PEN when cabling is exiting a building.


There is a lot on info on youtube on this including the Amendment 1


The Amendment is available from the IET website on the below link for viewing


https://electrical.theiet.org/bs-7671/updates-to-18th-edition/

Converting to TT for outbuildings

That's the method in the UK

Risteard81

As above it's converting to a TT system (not IT).

IT is generally illegal in the UK (except for specialist installations e.g. hospital operating theatres).

With EVSEs simultaneous contact between Earthing systems has to be considered, and now new O-PEN devices exist to allow use of TN-C-S. (It breaks the Earth connection as well as the neutral if loss of PEN is detected.) But that's all in the realm of BS7671 rather than ET101/I.S. 10101

2011

In the event of something going wrong none of this matters.
What is important is the high impedance of the earth fault path.
I would not accept this whether I was in the UK or the ROI.

Bruthal

2011 wrote: »

In the event of something going wrong none of this matters.
What is important is the high impedance of the earth fault path.
I would not accept this whether I was in the UK or the ROI.

This earth rodding of shed could simply be another sds drill engineer thinking an earth rod is a fine solid earthing method, without any further thought on it.

stickman1019

Risteard81 wrote: »

As above it's converting to a TT system (not IT).

IT is generally illegal in the UK (except for specialist installations e.g. hospital operating theatres).

With EVSEs simultaneous contact between Earthing systems has to be considered, and now new O-PEN devices exist to allow use of TN-C-S. (It breaks the Earth connection as well as the neutral if loss of PEN is detected.) But that's all in the realm of BS7671 rather than ET101/I.S. 10101

Apologies typo there it was meant to be TT.

Risteard81

2011 wrote: »

In the event of something going wrong none of this matters.
What is important is the high impedance of the earth fault path.
I would not accept this whether I was in the UK or the ROI.

In a UK single phase supply essentially you would have had no choice, as other options were wholly impracticable (and often impossible).

Now, in Amendment 1 to BS7671:2018 (only released on the 1st February 2020) there is an option for these new O-PEN devices on a single phase supply. Matt:e manufactures them, and as I stated they break the cpc connection as well as the phase and neutral. They are only coming onto the market now. I tried to source one with a Type B RCD but was told that it would be another few weeks/months before it's released and that pricing hasn't even been confirmed for it yet. Therefore I was left with the only option being to use the unamended BS7671:2018 (which can be done until I think July) and adopt a TT system for the EVSE installation. A simultaneous contact risk assessment needs to be carried out to ensure that exposed and extraneous-conductive-parts of the TN-C-S installation cannot be touched whilst charging the EV.

2011

You are missing the point. Physics doesn’t care about revaluations. If the casing of the boiler becomes live due to a fault I want the upstream MCB or fuse to disconnect the supply rapidly. If the earth fault loop impedance is too high this may not happen. As a result of this someone may be injured and no amount of quoting regulations that apply in foreign countries will be of any consolation to them.

Besides, this is the ROI not the UK.

stickman1019

Risteard81 wrote: »

In a UK single phase supply essentially you would have had no choice, as other options were wholly impracticable (and often impossible).

Now, in Amendment 1 to BS7671:2018 (only released on the 1st February 2020) there is an option for these new O-PEN devices on a single phase supply. Matt:e manufactures them, and as I stated they break the cpc connection as well as the phase and neutral. They are only coming onto the market now. I tried to source one with a Type B RCD but was told that it would be another few weeks/months before it's released and that pricing hasn't even been confirmed for it yet. Therefore I was left with the only option being to use the unamended BS7671:2018 (which can be done until I think July) and adopt a TT system for the EVSE installation. A simultaneous contact risk assessment needs to be carried out to ensure that exposed and extraneous-conductive-parts of the TN-C-S installation cannot be touched whilst charging the EV.

Do you have a link to Single Phase product ?

I heard they did a 3Ph one.


Below video is worth a watch.
https://youtu.be/9GzEL3WqcrQ

2011

Risteard81 wrote: »

Now, in Amendment 1 to BS7671:2018 (only released on the 1st February 2020) there is an option for these new O-PEN devices on a single phase supply. Matt:e manufactures them, and as I stated they break the cpc connection as well as the phase and neutral. They are only coming onto the market now. I tried to source one with a Type B RCD but was told that it would be another few weeks/months before it's released and that pricing hasn't even been confirmed for it yet. Therefore I was left with the only option being to use the unamended BS7671:2018 (which can be done until I think July) and adopt a TT system for the EVSE installation. A simultaneous contact risk assessment needs to be carried out to ensure that exposed and extraneous-conductive-parts of the TN-C-S installation cannot be touched whilst charging the EV.

@Risterad: sorry I am only reading this part of your post now, my bad. Looks interesting. Can you please start a new thread to discuss this as it does not really fit here?

Risteard81

stickman1019 wrote: »

Do you have a link to Single Phase product ?

I heard they did a 3Ph one.


Below video is worth a watch.
https://youtu.be/9GzEL3WqcrQ

https://www.cef.co.uk/catalogue/products/4873097-single-phase-voltage-monitoring-and-protection-unit

Risteard81

2011 wrote: »

@Risterad: sorry I am only reading this part of your post now, my bad. Looks interesting. Can you please start a new thread to discuss this as it does not really fit here?

Sure thing. Will do that a bit later.

Bruthal

stickman1019 wrote: »

Do you have a link to Single Phase product ?

I heard they did a 3Ph one.


Below video is worth a watch.
https://youtu.be/9GzEL3WqcrQ

I seen that exact scenario happen in a group of houses before. One I was called to had over 300v L-N in it.

If the houses all had similar loads on, voltages would be normal in them. Cooker on in one and bulb on in another, and bulb gets most of the 400v between the 2 houses phases.

Michelinextra.

Risteard81 wrote: »

In a UK single phase supply essentially you would have had no choice, as other options were wholly impracticable (and often impossible).

Now, in Amendment 1 to BS7671:2018 (only released on the 1st February 2020) there is an option for these new O-PEN devices on a single phase supply. Matt:e manufactures them, and as I stated they break the cpc connection as well as the phase and neutral. They are only coming onto the market now. I tried to source one with a Type B RCD but was told that it would be another few weeks/months before it's released and that pricing hasn't even been confirmed for it yet. Therefore I was left with the only option being to use the unamended BS7671:2018 (which can be done until I think July) and adopt a TT system for the EVSE installation. A simultaneous contact risk assessment needs to be carried out to ensure that exposed and extraneous-conductive-parts of the TN-C-S installation cannot be touched whilst charging the EV.

Can you expand on this a little , the O-PEN devices and the TT/TN-C-S

Maybe it's the drink again bit I'm not quite following it

Bruthal

Risteard81 wrote: »

https://www.cef.co.uk/catalogue/products/4873097-single-phase-voltage-monitoring-and-protection-unit

How does it see a difference in N to E potential if connected to the neutralized house?

stickman1019

Michelinextra. wrote: »

Can you expand on this a little , the O-PEN devices and the TT/TN-C-S

Maybe it's the drink again bit I'm not quite following it

I will try to assist the best I can.

The attached and below video from about 5:00 onwards will give you a understanding of the dangers of an Open PEN.

https://www.youtube.com/watch?v=FowcjLoMDUI


The next video is for the un-ammended version but still fairly relavent goes through in fairly good details the obstacles around the compliance and the only real option (local earth rod) before the the Matt-E products come on the scene.


https://www.youtube.com/watch?v=q87H7aIujjA

Bruthal

2011 wrote: »

@Risterad: sorry I am only reading this part of your post now, my bad. Looks interesting. Can you please start a new thread to discuss this as it does not really fit here?

Fairly simple device anyway, sort of like a voltage operated ELCB.

Very easy to make up a voltage detector circuit with a few components and get them to operate the contactor.

I am curious how it detects any voltage in a neutralized system if it is not measuring between N and an independant earth point.

Maybe i am missing something obvious.

Edit: It detects a drop in L-N voltage probably, when the N into the house fails. (L-N voltage reduces to a level depending on earth rod impedance and house load, bigger load = lower voltage L-N = higher touch voltage on N and E)

I wonder how it handles neutral failure if the main neutral to a mini pillar fails, in which case the L-N voltage can increase or decrease in a single phase house, as now we have multi single phase loads with no neutral (floating star point) . The L-N voltage here can go above 230v. So if it went to 330v in a house, the neutral is displaced 100v.

So the o-pen unit would have to detect voltages higher or lower than the expected 230v +/- tolerance between L and N, if that's what it measures, which seems likely. A time delay to eliminate voltage dips needed perhaps.

Another DIY microcontroller ADC application, and a simple one at that.