On the fiddle ______________

[Judd]

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ibb.co

Came across this setup today, upon further investigation i noticed the distributors neutral terminal completly slackened off in the meter (looked intentional) is this to prevent any possible current from returning via the meter?
With the 1g switch (just above DB) turned on the meter would read like normal. With the switch off the meter has no neutral and therfore is blank.

 

[mainline]

20230622-130147 hosted at ImgBB

Image 20230622-130147 hosted in ImgBB

ibb.co

Came across this setup today, upon further investigation i noticed the distributors neutral terminal completly slackened off in the meter (looked intentional) is this to prevent any possible current from returning via the meter?
With the 1g switch (just above DB) turned on the meter would read like normal. With the switch off the meter has no neutral and therfore is blank.

That needs sorting immediately.

They are using the Earth terminal as Neutral.

The supply to the meter shouldn't be affected unless the Neutral from the cutout was the one loosened ?

I suspect the switch when on is making a path to the N tail out of the meter hence the meter fires up, when the switch is off the meter goes off, but current still flows because of the Earth to Neutral connection.

Eelectricity theft in a very dangerous way.

 

[rewireIT]

If i've seen right, neutral is coming in, is blocked onto the t+e feeding the switch, which is using the brown as a switching wire for the neutral which then uses bonding cable to act as the main switches neutral?

Do the appliances work when the switch is off?

This is all kinds of whacky, never seen owt like this but it screams 'dead bodies'. Would report this to authorities immediately and would switch the lot off.

I like how they've grommetted their t+e into the board though. That's a conscientious sparky right there.

 

[mainline]

If i've seen right, neutral is coming in, is blocked onto the t+e feeding the switch, which is using the brown as a switching wire for the neutral which then uses bonding cable to act as the main switches neutral?

Do the appliances work when the switch is off?

This is all kinds of whacky, never seen owt like this but it screams 'dead bodies'. Would report this to authorities immediately and would switch the lot off.

I'm guessing it's not the type of meter which stops current flow when not energised.

The silly thing is that they still had to access and disconnect the supply neutral to the meter.

 

[rewireIT]

The silly thing is that they still had to access and disconnect the supply neutral to the meter.

What do you mean? Would the neutral from service head to meter not just stay in place in this rig?

 

[mainline]

What do you mean? Would the neutral from service head to meter not just stay in place in this rig?

If the L and Neutral remained from the cut-out then the meter would be powered whether the o/p tails were connected or not.

 

[rewireIT]

If the L and Neutral remained from the cut-out then the meter would be powered whether the o/p tails were connected or not.

I'm still struggling to see how this means the meter is registering usage when the 'light' switch is on.

We've got incoming tails, no neutral connected to the meter. Then L out N out of the meter, L goes to main switch, N is switched and goes to main switch via earth bar, which means the circuit must always be using earth as the return since there's no other neutral in the circuit? So when the switch is off, there is basically no actual neutral in the circuit, not in or out of the meter, and there will be a line into the CU and only an earth out, am i getting that right?

Basically would this not function exactly the same without the switched neutral at all?

I've done a sketch of what it looks like to me.

Key:

Mtr - Meter
SH - Service Head
SW - Switch
E - Earth bar
MS - Main switch

 

[timhoward]

@rewireIT I think you have it right, the only confusion is over how the meter behaves.
Yes, it would function exactly the same without the switch and the 'N' connection to meter in the sense that all final circuits would 'work'. It's equivalent to doing safe isolation and testing L to CPC bar to confirm polarity.

The point is that the meter (if digital) wont record anything without a return current path. The switch is providing a return current path. So when the switch is on, the meter electronics fire up and records some usage.

 

[Other_Tucker]

If the neutral and earth are joined together in the head TNC-S, can this just work as a switch?

Meter neutral supply to CU and Main CPC to CU - normal running conditions and meter functions, if someone hid a crossover switch so now Neutral from the CU then connects to earth and Main bonding cable becomes the neutral tail - I don't think electrically anything would be affected, RCD's etc and anything upstream of the theoretical switch wouldn't care.

If the meter only counts both L+N through it and not L+"Bypass N" Unscrupulous people could wire and hide a free elec / metered elec switch subtlety between the meter and the CU. I'm imagining some sort of rotary switchgear

 

[Judd]

I'm still struggling to see how this means the meter is registering usage when the 'light' switch is on.

We've got incoming tails, no neutral connected to the meter. Then L out N out of the meter, L goes to main switch, N is switched and goes to main switch via earth bar, which means the circuit must always be using earth as the return since there's no other neutral in the circuit? So when the switch is off, there is basically no actual neutral in the circuit, not in or out of the meter, and there will be a line into the CU and only an earth out, am i getting that right?

Basically would this not function exactly the same without the switched neutral at all?

I've done a sketch of what it looks like to me.

Key:

Mtr - Meter
SH - Service Head
SW - Switch
E - Earth bar
MS - Main switch

Diagram looks right to me,
I'm not sure if the meter was 'registering usage' it merely sprang to life.

The conclusion I came to is that the meter must need a neutral terminated 'to it' to operate and read correctly.

 

[rewireIT]

@rewireIT I think you have it right, the only confusion is over how the meter behaves.
Yes, it would function exactly the same without the switch and the 'N' connection to meter in the sense that all final circuits would 'work'. It's equivalent to doing safe isolation and testing L to CPC bar to confirm polarity.

The point is that the meter (if digital) wont record anything without a return current path. The switch is providing a return current path. So when the switch is on, the meter electronics fire up and records some usage.

Ah great i understand, thanks for that.

 

[rewireIT]

Diagram looks right to me,
I'm not sure if the meter was 'registering usage' it merely sprang to life.

The conclusion I came to is that the meter must need a neutral terminated 'to it' to operate and read correctly.

Definitely the most wild thing i've seen in terms of a bypass. People usually just henley block and have two separate CU's, one metered and one not, if they want to still record some usage. Can't see any other reason you would have the switch there if you didn't want it registering something.

Mad.

 

[rewireIT]

If the neutral and earth are joined together in the head TNC-S, can this just work as a switch?

Meter neutral supply to CU and Main CPC to CU - normal running conditions and meter functions, if someone hid a crossover switch so now Neutral from the CU then connects to earth and Main bonding cable becomes the neutral tail - I don't think electrically anything would be affected, RCD's etc and anything upstream of the theoretical switch wouldn't care.

If the meter only counts both L+N through it and not L+"Bypass N" Unscrupulous people could wire and hide a free elec / metered elec switch subtlety between the meter and the CU. I'm imagining some sort of rotary switchgear

How would you stop the neutrals from acting as proper neutrals though since they're all physically connected correctly in the board?

I'm trying to visualise a set up whereby the board can look normal but can be switched to use earth as neutral.

 

[Judd]

Definitely the most wild thing i've seen in terms of a bypass. People usually just henley block and have two separate CU's, one metered and one not, if they want to still record some usage. Can't see any other reason you would have the switch there if you didn't want it registering something.

Mad.

Yes maybe it does register usage so they can just toggle between 'free' and 'paid for' not to arise any suspicion, and/or if any one comes to check everything seems to operate correctly.

 

[rewireIT]

Yes maybe it does register usage so they can just toggle between 'free' and 'paid for' not to arise any suspicion, and/or if any one comes to check everything seems to operate correctly.

You know from your description of the neutral cut out tail this is exactly what's going on. Head is not in the same location as the board i presume? So if someone comes to read the meter they can toggle the switch and visually the neutral seems to be in the meter.

Can anyone explain now however why this is dangerous? It looks really poor (main neutral essentially switched with 2.5mm) but when actually thinking about it - if the N and E are connected in the head in a TNCS then really isn't this just doing what the head does but in the CU?

 

[timhoward]

Can anyone explain now however why this is dangerous?

You end up with the return path having a much smaller cross sectional area than the incoming live tail.
It would be like having a 25 sq mm Live tail and a 16 sq mm N tail. (I didn’t check the photo for actual sizes but you get the idea)

 

[Judd]

You end up with the return path having a much smaller cross sectional area than the incoming live tail.
It would be like having a 25 sq mm Live tail and a 16 sq mm N tail. (I didn’t check the photo for actual sizes but you get the idea)

The return 'fake neutral' is 16mm same as the live conductors, the consumer unit is fed by a 16mm 3core SWA.

 

[timhoward]

The return 'fake neutral' is 16mm same as the live conductors, the consumer unit is fed by a 16mm 3core SWA.

Ah ok. Well obviously there’s a list of regs one could cite that are being broken and the dangers associated with anyone trying to work on the main earth and finding the full return current passing through it, but otherwise I’d agree it’s essentially the same as a N-E link in the cut-out.
The main danger is probably that it isn’t as it should be and how we’d expect it to be.

 

[mainline]

You know from your description of the neutral cut out tail this is exactly what's going on. Head is not in the same location as the board i presume? So if someone comes to read the meter they can toggle the switch and visually the neutral seems to be in the meter.

Can anyone explain now however why this is dangerous? It looks really poor (main neutral essentially switched with 2.5mm) but when actually thinking about it - if the N and E are connected in the head in a TNCS then really isn't this just doing what the head does but in the CU?

I doubt smart meters would react like that, they would most probably report a power out or even a pen fault.

They have basically linked the cpc and neutral together at the earth bar and disconnected the N from one side of the N shunt in the meter.

The no separation of the CPC from neutral at all turning it into an IT system, How do you think the RCDs are going to react ?.

 

[timhoward]

The no separation of the CPC from neutral at all now turning it into an IT system,

I know what you are saying, but an IT system with no Isolating Transformer isn't really.....

How do you think the RCDs are going to react ?.

Erm, am I missing something as I'd say "the same?". The only difference between this and a correct setup is that there should be two conductors not one and the N-E link is the other side of the meter. The N for both RCD's still connects to the bottom of the main switch.

 

[mainline]

I know what you are saying, but an IT system with no Isolating Transformer isn't really.....

What sort of earthing system is it ?

 

[timhoward]

What sort of earthing system is it ?

It's Friday night and I started early.... but I'd say still TN-C-S really, Just the S is happening at the CPC bar not the cut-out.

The neutral is disconnected from the meter, so when the switch is open there is only one neutral conductor and that's the same one as the cpc,

completey agree

where is the separation of the cpc and neutral ?

The CPC bar. The main earth arrives there which is being misused as a PEN conductor. Imagine the G/Y conductor going to the main switch is blue. We don't have to agree! It's a crazy setup after all. But I think the RCDs would work.

 

[mainline]

I wonder why it was left like that and not removed when they left

 

[timhoward]

Do you think L to Cpc would trip the rcd ? or mcb ?

Yes. Forget the RCD a minute. If current can flow from the MCB through a load and back via the N bar, via the RCD, and the load works, then we've proved it's possible for current to flow. Lower the resistance, all the way to negligable if you like, and lots of current will flow, the and MCB will trip. Or has the 1664 completely broken my brain?

For the RCD, anything that goes through it on the L side and doesn't come back on the 'other pole' will cause an imbalance and it will trip.

If you take the meter completely out of the installation and forget it, this is electrically equivalent to every TN-C-S install. Just the point where PEN becomes N and CPC has shifted but it's still upstream of the RCDs.

 

[mainline]

Yes. Forget the RCD a minute. If current can flow from the MCB through a load and back via the N bar, via the RCD, and the load works, then we've proved it's possible for current to flow. Lower the resistance, all the way to negligable if you like, and lots of current will flow, the and MCB will trip. Or has the 1664 completely broken my brain?

For the RCD, anything that goes through it on the L side and doesn't come back on the 'other pole' will cause an imbalance and it will trip.

If you take the meter completely out of the installation and forget it, this is electrically equivalent to every TN-C-S install. Just the point where PEN becomes N and CPC has shifted but it's still upstream of the RCDs.

I need a holiday ....

 

[timhoward]

I need a holiday ....

No worries, it was a most welcome distraction from trying to reassemble an over-locker sewing machine....I'll explain in Arms in a minute...

 

[Other_Tucker]

How would you stop the neutrals from acting as proper neutrals though since they're all physically connected correctly in the board?

I'm trying to visualise a set up whereby the board can look normal but can be switched to use earth as neutral.

There are two large diameter cables going from the CU to the same point in the head, a blue and a green yellow. The blue passes through the meter and the other doesn't, swapping them won't affect the installation because they're joined anyway, essentially it's just a cable colour changing crossover switch.

The CSA is different 16mm-25mm if you're fussy , but if the deteriorating rubber DNO tails to the meter are 10mm anyway I can't see it being an issue

 

[davesparks]

What sort of earthing system is it ?

TN-C

 

[mainline]

There are two large diameter cables going from the CU to the same point in the head, a blue and a green yellow.

No there isn’t the blue conductor isn’t connected to the meters neutral as the incoming to the meter has been disconnected, leaving a switched shared cpu/neutral connected to the meters output.

 

[mainline]

TN-C

Thats what I thought but was more concerned with using a single conductor to combine N and Cpc I would have thought could upset an rcd.

 

[mainline]

Thats what I thought but was more concerned with using a single conductor to combine N and Cpc I would have thought could upset an rcd.

Residual current devices (RCD) rely on detecting currents flowing in the earthing conductor by measuring the out of balance currents between phase and neutral conductors. In a TN-C installation, the neutral and earthing conductor are combined, thus making the detection of residual current impossible.

You cannot tell what is a legitimate neutral current, and what is an earth fault current using the PEN, as the earth and neutral combined.

 

[timhoward]

In a TN-C installation, the neutral and earthing conductor are combined, thus making the detection of residual current impossible.

I don't think it's helpful to label this installation as a TN-C. I understand that in some ways that is correct, but it is causing confusion.
In a true TN-C system there wouldn't be an N or a CPC for any of the loads, just a PEN. In a true TN-C setup earth faults are indeed impossible to detect using an RCD.


In this installation, the neutral and earthing of loads are separated. The loads have N connected to the RCD and the CPC connected to the CPC bar. In turn, the CPC bar is connected to the N incomer on the main switch.
Therefore any current flowing through the CPC will not pass back through the RCD and the RCD will trip due to the imbalance.


Apart from the colour of the wire, I maintain that it is electrically exactly the same as this:


Discuss!

 

[Other_Tucker]

I cant find a ~100a version of the crossover switch in the picture, one that will link straight through L-R and then when turned join L green to R blue as well as L blue to R green. It's easy enough to do in electronics but I guess no-one makes an electric sized version. Sorry for the floppy CAD, turns out windows paint 3D is ----

 

[newfutile]

In a meter the neutral plays no part in the measurement unless its used to power (with the line) any electronics present in the meter .
i have taken single phase meters apart and there is always a solid neutral link with the live sent though a current shunt , the volt drop is then measured over the shunt to calculate amps

 

[mainline]

I cant find a ~100a version of the crossover switch in the picture, one that will link straight through L-R and then when turned join L green to R blue as well as L blue to R green. It's easy enough to do in electronics but I guess no-one makes an electric sized version. Sorry for the floppy CAD, turns out windows paint 3D is ----

A generator cross over switch or a contactor would do what you want.

I don't know how you would switch a 100amp mains using electronics cheaply.

I don't know what you are trying to achieve in your pic, The OPs had his N supply to the meter disconnected, so the meter electronics wouldn't work, as already said a number of times.

Apart from switching colours and Csa it won't do anything to thwart the meter reading.

 

[littlespark]

If it was as easy as disconnecting the neutral from the supply of the mainswitch…. And using earth as the return… basically not having anything connected to neutral out of the meter… to stop the meter running…. Everyone would be doing it.

The meters don’t need the neutral to operate… even the old mechanical ones.


Someone comes to read my meter 2 or 3 times a year, even though I fill it in online when asked to.
I’m sure these guys are trained to notice bypasses, strange boxes, smoking nails hammered into the tails….