Earth rod needed for shed supply or pme allowed ????

[Tim collins]

should you install a earth rod if running a feed to a shed which is built on timber frame and is all timber , no metal parts and will have no services ie gas or water in it so no need for bonding only a supply for a light and a couple of sockets or can you use a pme earth from fuseboard if the shed supply is run in 6mm armoured from the outside of the house ( inside house 6mm t+e to fuseboard ) protected by 32amp rcbo will be installing a 2 way board with rcd main switch in shed approx 25 meters away

 

[Midwest]

How do you know you have PME? you may have TNCS instead.

I have no idea what the difference is? I only say that, because at a job I said to a DNO engineer about a TNC-S supply, he said do you mean PME.

 

[MDJ]

PME is connected to earth at several points on the run to a house from the transformer, TNCS is not connected to earth several times on it's journey to your home. Regarding the earth rod, forget it, extend the existing earthing arrangement, popdorn at the ready

 

[Marvo]

I'd agree, if the building is not of metallic construction extend the existing earth whether the TN C S is PME'd or not. If it's PME you could also add a local rod for belt and braces, for pure TN C S certain external faults could result in very high earth currents so I probably wouldn't.

 

[Midwest]

PME is connected to earth at several points on the run to a house from the transformer, TNCS is not connected to earth several times on it's journey to your home. Regarding the earth rod, forget it, extend the existing earthing arrangement, popdorn at the ready

I suspect most houses are supplied as TNCS not PME as per your definition, but the DNO still calls its supplies to a property as PME.

 

[Nigel]

Jes, is this still going on

I know. Sorry.

I think @darkwood has completly misunderstood PME, extending EBZs and metallic buildings but there is only so much you can discuss in text so I will move on.

 

[Nigel]

It’s funny but I was talking to the guys from the DNO on a new build site a few weeks ago, all new supply’s to the homes are tncs.
I asked how far apart do you apply the earth electrodes for the pme connection, he said there’s a rod at the transformer end and a rod at the end of the cable , that’s it.
Now one guy was connecting up the street lighting and one guy applying a joint for 2 supplies to some properties but both said the same thing.

This is my point. We cannot know what is going on on the DNO side so it is irrelevant to the design process. All we need is the earthing arrangment supplied to us and BS7671 guides us from there.

 

[Nigel]

I suspect most houses are supplied as TNCS not PME as per your definition, but the DNO still calls its supplies to a property as PME.

I think any joint put in by the DNO will have an earth tap installed as standard so probably easier for the DNO to call it PME as a TN-C-S could become a PME at any time.

 

[Midwest]

I think any joint put in by the DNO will have an earth tap installed as standard so probably easier for the DNO to call it PME as a TN-C-S could become a PME at any time.

I'm no expert here. I've relayed a story before, when I had an issue with a TNS supply. A DNO engineer turned up. I asked if I could have it converted to a TNC-S supply, he said whats that in English, do you mean PME? He said, it would take 6 weeks, do it yourself, and demonstrated how to do so (I didn't take his advice).

So does TN-C-S in reality exist, all is it just a load of PME bull?

 

[Nigel]

I'm no expert here. I've relayed a story before, when I had an issue with a TNS supply. A DNO engineer turned up. I asked if I could have it converted to a TNC-S supply, he said whats that in English, do you mean PME? He said, it would take 6 weeks, do it yourself, and demonstrated how to do so (I didn't take his advice).

So does TN-C-S in reality exist, all is it just a load of PME bull?

I think it probably does exist on supplies with no joints and that have had no work done. I bet the DNO have no idea what supplies are and what supplies are not so just say all TN-C-S supplies are PME.

 

[westward10]

I know. Sorry.

I think @darkwood has completly misunderstood PME, extending EBZs and metallic buildings but there is only so much you can discuss in text so I will move on.

Why do you keep quoting EBZ that went out with the Spice Girls.

 

[Midwest]

Why do you keep quoting EBZ that went out with the Spice Girls.

I thought they were 'In' again?

 

[Nigel]

Why do you keep quoting EBZ that went out with the Spice Girls.

Do you know what an EBZ is?

 

[Darkwood]

I have TNCS at home, it is connected to a converted TT, this is now classed as a TNCS, a TNCS can be supplied in a concentric cable or conversion of a TT or TNS system where all they have done is strapped both the E/N together where the earth existed or made the N in a TT the N/E, the ability to do this is done on a case by case to ensure it is a safe option as oppose to running new supplies.

PME (Protective multiple Earthing) is exactly what it says on the tin, the concentric cable is earthed a regular intervals all of which can be inspected and tested but that is the DNO's side and duty.

PME/TNCS system stop at the cutout of the property where you are provided a common terminal or in some cases they split to 2 terminals to take a N and E from, within this thread and the title people discuss extending PME, this is wrong, that is a very different system and would mean you extended the combined N/E with a concentric cable and depending on length you may have to strap it down along it length, this has to be agreed with the DNO and cannot be done as an option otherwise. The E/N facility that the DNO supply at there cutout is where PME or TNCS stops and you tap you N and E to as separate cables, once you have separated them your installation is based on a TNS design thus no circuits past the DNO's facility can be called PME or TNCS hence my continuous repeated point that you cannot word it as extending the PME.

 

[Darkwood]

Why do you keep quoting EBZ that went out with the Spice Girls.

I also was only using the Term because essex introduced it into the conversation and been old hat I continued its use, it still exists but under a new guise that is all, the actually application and practice hasn't changed but EBZ was deemed confusing if I recall so they changed it by name only.

 

[Nigel]

I have TNCS at home, it is connected to a converted TT, this is TNCS, a TNCS can be supplied in a concentric cable or conversion of a TT or TNS system where all they have done is strapped both the E/N together where the earth existed or made the N in a TT the N/E, the ability to do this is done on a case by case to ensure it is a safe option as oppose to running new supplies.

PME (Protective multiple Earthing) is exactly what it says on the tin, the concentric cable is earthed a regular intervals all of which can be inspected and tested but that is the DNO's side and duty.

PME/TNCS system stop at the cutout of the property where you are provided a common terminal to take a N and E from, within this thread and the title people discuss extending PME, this is wrong, that is a very different system and would mean you extended the combined N/E with a concentric cable and depending on length you may have to strap it down along it length, this has to be agreed with the DNO and cannot be done as an option otherwise. The E/N facility that the DNO supply at there cutout is where PME or TNCS stops and you tap you N and E to as separate cables, once you have separated them your installation is based on a TNS design thus no circuits past the DNO's facility can be called PME or TNCS hence my continuous repeated point that you cannot word it as extending the PME.

Everyone knows what is meant when they say 'extending the PME'. Nobody means physically extending it and taking over the DNO's job.

It is like correcting someone for saying 'sub-main' or 'ring main'. We all know what is meant and no real need to correct it.