Extranous conductive parts or exposed

newfutile · Apr 12, 2023

During an EICR I have found an isolator with no cpc present bolted to a large metal post and all the motorized metal car park gate, the fact that the isolator has been moved but the cpcs are not present.

I get a zs from the metalwork of 36 ohms, as the wires pass though I class this as exposed conductive parts.

No rcd is present on the gate circuit.
Would all the rest of the metalwork fixed in the ground count as extranous?

timhoward · Apr 12, 2023

Is is fed by an SWA cable? Just wondering if isolator has been moved whether it once used the armour as a cpc....

buzzlightyear · Apr 12, 2023

newfutile said:
No rcd is present on the gate circuit.
Would all the rest of the metalwork fixed in the ground count as extranous?

Where is the feed from.

Lucien Nunes · Apr 12, 2023

Extraneous conductive parts are those liable to introduce a potential usually into a defined equipotential zone. E.g. if the equipotential is created within a building by bonding and earthing to the MET, then an incoming pipe could introduce a different potential if not bonded. But if the conductive part / metal structure is entirely outside, it's not really introducing a potential to anywhere, as it will be at the surrounding equipotential of true earth.

timhoward · Apr 12, 2023

Even though the thread subject said "extraneous", the post said "exposed" which is probably closer to the mark, depending on the details. If there are single insulated conductors inside the metal post, at that point be concerned about the post being an exposed conductive part, and the lack of earthing.
Do you have any pictures?
Obviously the general 'lack of CPC' situation is a separate topic in it's own right.

newfutile · Apr 13, 2023

I am visiting the property again today where I will have more time to investigate and take pictures , it is fed by armoured which then goes inside a metal hollow square post,the isolator is bolted to this.

newfutile · Apr 13, 2023

I'm here again, it's fed from swa to a fcu then more swa into the metal column, inside the metalwork are single insulated wires, no idea what happened to the cpc.

If I connect up a cpc should it just be a cpc, or do I treat it as extranous and run a 10mm bonding conductor to all the metal work?

timhoward · Apr 13, 2023

That's quite an interesting one.

It's your EICR, but in this instance I'd focus on accurately saying what I think is wrong rather than trying to fix it to avoid coding it.
My thoughts -
1 - look at the load that is downstream from the isolator - is there any sign of a CPC, and what does it measure back to the FCU and the MET. If there isn't an adequate CPC from origin to load then that's a C2.
2 - I'd treat the post as steel trunking, it's become part of the electrical installation and has single insulated conductors inside it. I'd argue that is therefore an exposed conductive part and it should be earthed. At the moment the post would become live (save a 37 ohm path to real earth) if something happened to the singles inside it. That's a C2.
3 - I'd be concerned what is going on out of sight inside the post, whether there are any SWA glands (looks unlikely), lack of grommets by the look of it, if there is a CPC connection using the steel armour and how it is made. Unless you have an inspection camera with you that might have to be an FI, though I think I spy a C2 for lack of grommets from the photo, especially as it's not earthed.

For remedial work I'd be more inclined to work out how I could a better job with proper SWA terminations than start fiddling with it. e.g. possibly bring the SWA out nearer the bottom, gland it into a galv conduit box , surface mount galv up the isolator, and go from there.

newfutile · Apr 13, 2023

I work as an electrical inspector for a housing association, i cant give an unsatisfactory EICR except in rare circumstances, therefore it’s usually down to me to fix it and report the work as remedial .

The load appears to be a motor inside the caged area, I suppose I could test to the casing .
The outer of the armour appears to be earthed , I think it can’t be glanded inside the metal post.

I will ensure cpc continuity to the post and circuit end points .

Does the metalwork also count as extraneous ? , im thinking of diverted neutral currents .
however it seems to be TN-S supply as the supply has a SNE SYSTEM label.

Also once a cpc is connected the adjacent gate metalwork could be at a different potential !

Gnasher · Apr 13, 2023

timhoward said:
That's quite an interesting one.

It's your EICR, but in this instance I'd focus on accurately saying what I think is wrong rather than trying to fix it to avoid coding it.
My thoughts -
1 - look at the load that is downstream from the isolator - is there any sign of a CPC, and what does it measure back to the FCU and the MET. If there isn't an adequate CPC from origin to load then that's a C2.
2 - I'd treat the post as steel trunking, it's become part of the electrical installation and has single insulated conductors inside it. I'd argue that is therefore an exposed conductive part and it should be earthed. At the moment the post would become live (save a 37 ohm path to real earth) if something happened to the singles inside it. That's a C2.
3 - I'd be concerned what is going on out of sight inside the post, whether there are any SWA glands (looks unlikely), lack of grommets by the look of it, if there is a CPC connection using the steel armour and how it is made. Unless you have an inspection camera with you that might have to be an FI, though I think I spy a C2 for lack of grommets from the photo, especially as it's not earthed.

For remedial work I'd be more inclined to work out how I could a better job with proper SWA terminations than start fiddling with it. e.g. possibly bring the SWA out nearer the bottom, gland it into a galv conduit box , surface mount galv up the isolator, and go from there.

Agree with this.
In addition I would also be checking for negligible resistance between simultaneously accessible parts.

newfutile · Apr 17, 2023

This area is under the flats , the gates secure the car parking area, this also has electrics in it for lighting ,cctv, separator units and so on.
I can’t see that if I reinstate the cpc it’s unlikely that the metalworks will be at negligible resistance on the metalworks , therefore I will have to bond them together .
would this then require a 10mm bonding conductor to the MET?

timhoward · Apr 18, 2023

newfutile said:
This area is under the flats , the gates secure the car parking area, this also has electrics in it for lighting ,cctv, separator units and so on.
I can’t see that if I reinstate the cpc it’s unlikely that the metalworks will be at negligible resistance on the metalworks , therefore I will have to bond them together .
would this then require a 10mm bonding conductor to the MET?

I suspect you may be over thinking this one.
Exposed conductive parts need earthing.
Extraneous conductive parts need bonding. To be extraneous they need to be able to introduce a potential from outside the immediate area, and not be part of the electrical system.

Obviously I've not been there. It sounds as though the CPC situation needs sorting, and the terminations in the post need checking/sorting. If there are single insulated conductors in the post, it needs earthing.
Beyond that I'm struggling to see anything that's potentially dangerous.

Once the post is earthed and anything class 1 in terms of lighting, cctv is earthed then any faults should cause ADS before a person can touch any of it. Have you come up with another dangerous scenario that I'm missing?

Gnasher · Apr 18, 2023

newfutile said:
This area is under the flats , the gates secure the car parking area, this also has electrics in it for lighting ,cctv, separator units and so on.
I can’t see that if I reinstate the cpc it’s unlikely that the metalworks will be at negligible resistance on the metalworks , therefore I will have to bond them together .
would this then require a 10mm bonding conductor to the MET?

Hi
Remember we are not talking main protective bonding conductors.

Take a look at Table 4.6 in the on site guide.

newfutile · Apr 18, 2023

Part of the gate has a motor , the other parts including a pedestrian gate (selv magnet) is metalwork in concrete , the same with the other metal fencing for lack of a better term,these will be simultaneous touchable with the exposed metalwork which is also partially buried in concrete . Gn8 states that its extraneous if the IR is less than 23 k for 10ma ,currently there is no (RCD) Residual Current Device

Gnasher · Apr 18, 2023

newfutile said:
Part of the gate has a motor , the other parts including a pedestrian gate (selv magnet) is metalwork in concrete , the same with the other metal fencing for lack of a better term,these will be simultaneous touchable with the exposed metalwork which is also partially buried in concrete . Gn8 states that its extraneous if the IR is less than 23 k for 10ma ,currently there is no (RCD) Residual Current Device

Take a look at this.

https://www.bing.com/ck/a?!&&p=10fc595ee231e5e7JmltdHM9MTY4MTc3NjAwMCZpZ3VpZD0yM2U0NzFkNy1mZjZmLTYxMWMtM2RiMy02MzIwZmU4ZjYwODYmaW5zaWQ9NTIxMg&ptn=3&hsh=3&fclid=23e471d7-ff6f-611c-3db3-6320fe8f6086&psq=is+it+an+extrainious+conductive+part&u=a1aHR0cHM6Ly9lbGVjdHJpY2FsYXBwcmVudGljZS5jby51ay9ob3ctZG8taS1kZXRlcm1pbmUtYW4tZXh0cmFuZW91cy1jb25kdWN0aXZlLXBhcnQv&ntb=1

What page in Gn8 are looking at?

Extranous conductive parts or exposed

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