Why are main bonding conductors so big?

[Dan Martin]

Am guessing your thinking of an old PILC supply into a property where a modern cutout has been fitted to it?

 

[OnOff]

Shamelessly stealing off Andy but can't the forum home page be changed to include ".....PME is always TN-C-S, but TN-C-S is not always PME!....." maybe scrolling across the top?

 

[Dan Martin]

On a modern combined neutral earth mains cable, TNC-s supply, each joint along the main has an earth tail coming out of it tying the neutral to earth. Thus PME and tncs. If the original mains cable was separate neutral earth and was converted to pme, joints along that cable will have the neutral, earth and armour bonded including an earth tail. Even if there is still a separate neutral and earth conductor coming to the premises, once it has been labeled pme those two conductors are in effect one because of the way it has been bonded in the joint, making it tncs even though there is still that earth coming to the premises. Once a cable has a shared neutral earth conductor under ESQCR regs that neutral must be tied down to earth at a point no closer than the junction of the service from the main. So once that combined N/E is provided, it will be PME'd at some point along that main cable

I suppose you could connect to a pme main and choose not to use the earth and use your own, but pointless.

 

[Andy™]

some buildings with their own transformer may only have 1 earth rod connected to transformer. so TNCS, but not PME

 

[Dan Martin]

Just thought of the exception, swimming pools and petrol stations when there is no separate earth and you have to provide your own. PME supply with tt earthing

 

[Steve3948]

People keep going on about metal services coming into houses, well where's all that Yellow and Blue stuff going then, even older places have a black water pipe, I cannot remember seeing metal services for years.

I hate TT its looks s**t, it's an added job that I can do without unless it's the only way, give me TNC-S and PME any day.

 

[Dan Martin]

[quote name='Andy

 

[steptoe]

Then that building with the transformer is using the transformers TME as its termination into the premises, that switchgear will have a cable run to earth providing the PME. Btw TNC-s stands for Terra Neutral Combined - Seperate (Earth Neutral combined, separated at termination) For earth and neutral to be combined it HAS to be pme under ESQCR. If not either separate earth conductor or provide your own via TT

give me a quote on that please?

the other fact to be borne on mind is that even though it is labelled as PME do you actually test it to prove this fact?

 

[Andy™]

Then that building with the transformer is using the transformers TME as its termination into the premises, that switchgear will have a cable run to earth providing the PME. Btw TNC-s stands for Terra Neutral Combined - Seperate (Earth Neutral combined, separated at termination) For earth and neutral to be combined it HAS to be pme under ESQCR. If not either separate earth conductor or provide your own via TT

if there is only 1 rod, then it cannot be PME due to the lack of the multiple part

 

[Dan Martin]

give me a quote on that please?the other fact to be borne on mind is that even though it is labelled as PME do you actually test it to prove this fact?

my bad, its shall

Protective multiple earthing

9.

 

[Andy™]

If it is an industrial supply then the CT cabinet will have a line to earth connected to the neutral and to earth. Hey presto, PME'd

your missing the point, unless there are 2 or more rods it cannot be PME regardless of what other links you add

 

[Jono Pashley]

If all thats happening is the N+E are being bonded together every so often i fail to see how that can be called PME as no Earthing as such is taking place.

 

[Dan Martin]

Then without that multiple earthing it cant be TNC-S as stipulated by the regs. Thats not to say there is an incorrect sticker on an installation.

---------- Post Auto-Merged at 20:58 ---------- Previous post was made at 20:57 ----------

If all thats happening is the N+E are being bonded together every so often i fail to see how that can be called PME as no Earthing as such is taking place.

Each joint where the two are bonded an earth tail is sent out into the ground

 

[Sidewinder]

Dan,

Have you heard of, & do you understand the concept of PNB?

Also, you may always rod a joint, but this has not always been so, by others, as, there was not always the requirement.

For PME, you must have multiple earth points. You cannot have PME with a single earth rod at a dedicated transformer only.

You must have multiple rods or other means of earthing Lang the LV supply to achieve TN-C-S.

You have quoted from the current ESQCR it seems.

This is like saying that all premises, have an RCD for s.o not under the control of skilled persons, because the current version of BS7671 says it must be that way

 

[Dan Martin]

Have heard of pnb but dont have much dealing wih is as I work U/G, its where the N/E is provided from a point away from the transformer and the premises? Will hold my hands up if that can be classed as tnc-s. But have always been told that for an installation to be given tnc-s it has to be pme.

Am in agreement that there needs to be multiple earths. Direct supply from tx would have one at the tx and one at termination. But thats on industrial supply.

Thats true, I cant vouch for other peoples joints so in theory there could be no earth connected to any joints.

Only quoted esqcr as it was pretty definitive on when neutral and earth are combined there shall be multiple earthing.

 

[steptoe]

Have heard of pnb but dont have much dealing wih is as I work U/G, its where the N/E is provided from a point away from the transformer and the premises? Will hold my hands up if that can be classed as tnc-s. But have always been told that for an installation to be given tnc-s it has to be pme.Am in agreement that there needs to be multiple earths. Direct supply from tx would have one at the tx and one at termination. But thats on industrial supply.

Thats true, I cant vouch for other peoples joints so in theory there could be no earth connected to any joints.

Only quoted esqcr as it was pretty definitive on when neutral and earth are combined there shall should be multiple earthing.

and that is the problem, its not always done.

 

[Dan Martin]

It seems PNB systems are open to interpretation. Even the wiring regs book says that a TNS systems can be considered to be TNCS PNB

 

[steptoe]

People keep going on about metal services coming into houses, well where's all that Yellow and Blue stuff going then, even older places have a black water pipe, I cannot remember seeing metal services for years.I hate TT its looks s**t, it's an added job that I can do without unless it's the only way, give me TNC-S and PME any day.

it looks as bad as the person that installed it,

myself? I much prefer function over form, making it look good is simply a by-product of good workmanship

so which is it? PME, or TNCS, that you prefer?

 

[Steve3948]

it looks as bad as the person that installed it, myself? I much prefer function over form, making it look good is simply a by-product of good workmanship

so which is it? PME, or TNCS, that you prefer?

Well for me it's PME, and in our area it's pretty available everywhere even out in the Cotswold sticks where they have a lot of O/H lines every 3rd pole has a spike down.

They are pretty strict on the 0.35 though.

My rods are the dogs, but I only seem to do one every 5 years or so, in fact today I went to cut one out (not mine) as Scottish and Southern had provided PME at 0.16 and he wanted it removed from outside his front door and I mean right outside, about 100mm to the side of the frame, although he said it was handy for scraping mud off his shoes.

 

[steptoe]

Well for me it's PME, and in our area it's pretty available everywhere even out in the Cotswold sticks where they have a lot of O/H lines every 3rd pole has a spike down.They are pretty strict on the 0.35 though.

My rods are the dogs, but I only seem to do one every 5 years or so, in fact today I went to cut one out (not mine) as Scottish and Southern had provided PME at 0.16 and he wanted it removed from outside his front door and I mean right outside, about 100mm to the side of the frame, although he said it was handy for scraping mud off his shoes.

well thats just pi55 poor workmanship, it should be flush with the surrounding area,

the other thingis, I hate those stupid little plastic boxes that so many people use, I much prefer a proper 'TOBY' box mesel.

these arent too bad,

but these are much more to my liking.