Earthing a "Portacabin"

[ADS]

ADS,You have now confused me!

Not difficult at this time!

I'm saying the DNO's change the local area cabling from TN-S to PME without telling anyone and have been doing for 20+ years.

It is only the last link to the premises they don't change.

Perhaps you'd better have another go, or I'd better come back later on after some sleep!!!

Sidewinder, I agree with you - it's Andy I was disagreeing with.

They can, and will, change the supply to a PME system - which, in effect, means the earth can then be tapped off the neutral in the cutout.

If the original TNS earth fails, it can then be converted to TNCS at the cutout.

Andy is trying to imply that although you have your earthing conductor clamped to the sheath of the supply cable (TNS), it might not be TNS, as the DNO might have connected the sheath to the neutral at some point further up the supply cable - in effect giving you TNC-S without telling you.

This I disagree with.

---------- AUTO MERGE Post added at 00:18 ---------- Previous post was at 00:15 ----------

I never assume

 

[Sidewinder]

ADS,

This seems to be what I am saying too, and you are agreeing with?

e.g.

The DNO changes the cable in the street, this will now be PME.

They don't change the final legs to the properties.

These are TN-S at the presentation.

HOWEVER, in the street the TN-S is now CNE/PME/TN-C-S.

Thus the TN-S presentation is actually not, but one would not normally know.

Time for be me thinks too much thinking for this time in the a.m. & too much of Guinness

 

[Sidewinder]

ADS,

This seems to be what I am saying too, and you are agreeing with?

e.g.

The DNO changes the cable in the street, this will now be PME.

They don't change the final legs to the properties.

These are TN-S at the presentation.

HOWEVER, in the street the TN-S is now CNE/PME/TN-C-S.

Thus the TN-S presentation is actually not, but one would not normally know.

Time for be me thinks too much thinking for this time in the a.m. & too much of Guinness

 

[steptoe]

Sidewinder, I agree with you - it's Andy I was disagreeing with.They can, and will, change the supply to a PME system - which, in effect, means the earth can then be tapped off the neutral in the cutout.

If the original TNS earth fails, it can then be converted to TNCS at the cutout.

Andy is trying to imply that although you have your earthing conductor clamped to the sheath of the supply cable (TNS), it might not be TNS, as the DNO might have connected the sheath to the neutral at some point further up the supply cable - in effect giving you TNC-S without telling you.

This I disagree with.

---------- AUTO MERGE Post added at 00:18 ---------- Previous post was at 00:15 ----------

I never assume

supply is an ass,

not having a go at you,

just trying to make a point to some not to guess or assume.

WE ALL KNOW BETTER dont we children.?

 

[steptoe]

Sidewinder, I agree with you - it's Andy I was disagreeing with.They can, and will, change the supply to a PME system - which, in effect, means the earth can then be tapped off the neutral in the cutout.

If the original TNS earth fails, it can then be converted to TNCS at the cutout.

Andy is trying to imply that although you have your earthing conductor clamped to the sheath of the supply cable (TNS), it might not be TNS, as the DNO might have connected the sheath to the neutral at some point further up the supply cable - in effect giving you TNC-S without telling you.

This I disagree with.

---------- AUTO MERGE Post added at 00:18 ---------- Previous post was at 00:15 ----------

I never assume

supply is an ass,

not having a go at you,

just trying to make a point to some not to guess or assume.

WE ALL KNOW BETTER dont we children.?

 

[ADS]

ADS,This seems to be what I am saying too, and you are agreeing with?

e.g.

The DNO changes the cable in the street, this will now be PME.

They don't change the final legs to the properties.

These are TN-S at the presentation.

HOWEVER, in the street the TN-S is now CNE/PME/TN-C-S.

Thus the TN-S presentation is actually not, but one would not normally know.

Time for be me thinks too much thinking for this time in the a.m. & too much of Guinness

Kind of.

They 'rod' (for want of a better word), the supply neutral, which gives you the PME supply.

The operative word is Protective Multiple Earthing - multiple simply means more than one - so they could 'rod' the supply twice or ten times.....it's still PME (I think this is Steptoes grievance with PME)

Now, if your house had a TNS earthing system before they convert their supply neutral, it will still be a TNS earthing system after they convert their supply - the TNS applies to the earthing system provided to the installation, not what the supply is capable of providing.

Think of it this way - If we took Steptoes advice and converted all TNCS (PME) installs to TT, then the installations would be TT, regardless of the fact that the supply neutral is still a PEN conductor with PME supply.

In the same way your installation is still TNS, until such time as the DNO allow connection of your 'earthing conductor' to the neutral, then it becomes TNCS.

 

[ADS]

ADS,This seems to be what I am saying too, and you are agreeing with?

e.g.

The DNO changes the cable in the street, this will now be PME.

They don't change the final legs to the properties.

These are TN-S at the presentation.

HOWEVER, in the street the TN-S is now CNE/PME/TN-C-S.

Thus the TN-S presentation is actually not, but one would not normally know.

Time for be me thinks too much thinking for this time in the a.m. & too much of Guinness

Kind of.

They 'rod' (for want of a better word), the supply neutral, which gives you the PME supply.

The operative word is Protective Multiple Earthing - multiple simply means more than one - so they could 'rod' the supply twice or ten times.....it's still PME (I think this is Steptoes grievance with PME)

Now, if your house had a TNS earthing system before they convert their supply neutral, it will still be a TNS earthing system after they convert their supply - the TNS applies to the earthing system provided to the installation, not what the supply is capable of providing.

Think of it this way - If we took Steptoes advice and converted all TNCS (PME) installs to TT, then the installations would be TT, regardless of the fact that the supply neutral is still a PEN conductor with PME supply.

In the same way your installation is still TNS, until such time as the DNO allow connection of your 'earthing conductor' to the neutral, then it becomes TNCS.

 

[Larnacaman]

SideWinder,

Do you have any idea as yet, to what these Group1 medical rooms are going to be used for?? There are also subsections for medical Group1 rooms being A and B. Normally the highest rating of group 1 rooms are designated as ''minor operating room'' ie, Cesarean birthing room etc.

What i still can't understand, is how come, or why, these facilities are located in domestic gardens?? Well in this case at least, according to your previous posts on this thread.....

 

[Larnacaman]

SideWinder,

Do you have any idea as yet, to what these Group1 medical rooms are going to be used for?? There are also subsections for medical Group1 rooms being A and B. Normally the highest rating of group 1 rooms are designated as ''minor operating room'' ie, Cesarean birthing room etc.

What i still can't understand, is how come, or why, these facilities are located in domestic gardens?? Well in this case at least, according to your previous posts on this thread.....

 

[ADS]

This is from 'Scottish Powers' - LOW VOLTAGE EARTHING POLICY AND

APPLICATION GUIDE.

I would imagine most DNOs follow similar guidelines.

The earthing of LV networks and the provision of earth terminals to customers can generally be

achieved in one of three ways:

 

[ADS]

This is from 'Scottish Powers' - LOW VOLTAGE EARTHING POLICY AND

APPLICATION GUIDE.

I would imagine most DNOs follow similar guidelines.

The earthing of LV networks and the provision of earth terminals to customers can generally be

achieved in one of three ways:

 

[Sidewinder]

Larnacaman,

Yes I do there are many of them around and there are also 2 other variations, where the install is in the patients home, at 2 different levels of complexity.

They are haemodialysis rooms.

They only come under the requirements of G1 no other, there is no standby power requirement.

I've worked on about a dozen of them now for various things.

I have also done about 3 complete installs of what we call the minimal room conversion.

 

[Sidewinder]

Larnacaman,

Yes I do there are many of them around and there are also 2 other variations, where the install is in the patients home, at 2 different levels of complexity.

They are haemodialysis rooms.

They only come under the requirements of G1 no other, there is no standby power requirement.

I've worked on about a dozen of them now for various things.

I have also done about 3 complete installs of what we call the minimal room conversion.

 

[Andy™]

So you are telling us that the DNO would connect the outer sheath of their supply cable to the neutral conductor at some random point on their network, and not tell anyone that the supply they thought was TN-S was now running part of the way on a PEN conductor!!

yes, they would. all the time. the neutral may well be capable of being a PEN conductor, and when another branch is taken from it, they normally bond neutral & earth at that point.

also, cant be bothered to look now, but you will find the odd post on here asking earthing type where there is a link between neutral & lead sheath at the service head due to fault with sheath. property with link would be TNCS, but the next house relying on the same sheath without the link would be presented as TNS, have a good earth loop, but be earthed from the PME neutral-earth bond in the other property.

are you now saying that doesnt happen either?

---------- AUTO MERGE Post added at 09:19 ---------- Previous post was at 09:12 ----------

Now, if your house had a TNS earthing system before they convert their supply neutral, it will still be a TNS earthing system after they convert their supply - the TNS applies to the earthing system provided to the installation, not what the supply is capable of providing.

im not disagreeing with what the supply is presented as. the fact is, even if its presented as TNS, you can guarantee the earth will be bonded to neutral more than just at the transformer, so its not a true TNS supply

 

[Andy™]

So you are telling us that the DNO would connect the outer sheath of their supply cable to the neutral conductor at some random point on their network, and not tell anyone that the supply they thought was TN-S was now running part of the way on a PEN conductor!!

yes, they would. all the time. the neutral may well be capable of being a PEN conductor, and when another branch is taken from it, they normally bond neutral & earth at that point.

also, cant be bothered to look now, but you will find the odd post on here asking earthing type where there is a link between neutral & lead sheath at the service head due to fault with sheath. property with link would be TNCS, but the next house relying on the same sheath without the link would be presented as TNS, have a good earth loop, but be earthed from the PME neutral-earth bond in the other property.

are you now saying that doesnt happen either?

---------- AUTO MERGE Post added at 09:19 ---------- Previous post was at 09:12 ----------

Now, if your house had a TNS earthing system before they convert their supply neutral, it will still be a TNS earthing system after they convert their supply - the TNS applies to the earthing system provided to the installation, not what the supply is capable of providing.

im not disagreeing with what the supply is presented as. the fact is, even if its presented as TNS, you can guarantee the earth will be bonded to neutral more than just at the transformer, so its not a true TNS supply

 

[ADS]

[quote name='Andy

 

[ADS]

[quote name='Andy

 

[Andy™]

I would say they would earth (rod) the neutral at that point - that's not the same thing as 'combining' the two conductors at that point and making it TNC./QUOTE]

unfortunately not.

ive only seen a rod be installed a few times (often its just a join without rod). they always short N&E at the join. if there is a rod going in, then the rod is connected to both N&E

---------- AUTO MERGE Post added at 09:36 ---------- Previous post was at 09:33 ----------

This I fully agree with - the property with the link to neutral will be TNCS - the connection to the sheath will be left in as this sheath is , in effect, an Extraneous Conductive Part and so requires bonding.But I agree, there would be an inadvertant link to the neutral for the other property

i think the link is there for more than just bonding it because its extraneous. depending where the lead sheath has lost its earth, it may effect more than 1 property. in which case, the link wont be an inadvertant link for the next property, it will be the other property's earth

 

[Andy™]

I would say they would earth (rod) the neutral at that point - that's not the same thing as 'combining' the two conductors at that point and making it TNC./QUOTE]

unfortunately not.

ive only seen a rod be installed a few times (often its just a join without rod). they always short N&E at the join. if there is a rod going in, then the rod is connected to both N&E

---------- AUTO MERGE Post added at 09:36 ---------- Previous post was at 09:33 ----------

This I fully agree with - the property with the link to neutral will be TNCS - the connection to the sheath will be left in as this sheath is , in effect, an Extraneous Conductive Part and so requires bonding.But I agree, there would be an inadvertant link to the neutral for the other property

i think the link is there for more than just bonding it because its extraneous. depending where the lead sheath has lost its earth, it may effect more than 1 property. in which case, the link wont be an inadvertant link for the next property, it will be the other property's earth

 

[ADS]

I'm not contradicting you now, Andy, just want to make a point.

Does what you describe not make a joke of the requirements laid down for a PME supply, if they're just going to randomly combine N and E anyway?

Also, what about all the advice given stating "If it's TNS, it's okay to run the earth to your garage or shed".....a bit dangerous if you are being kidded and the N and E are combined just down the road.