Earthing a "Portacabin"

[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.

 

[Andy™]

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.

thats part of the problem ADS....

if its presented as TNS, then it should be TNS all the way to star. but unfortunately they PME just about everything, so even if you have TNS, and you know its PME'd outside property, then working to 7671 you still have to treat it as TNS.

if its a lead cable, then you do have the advantage that the sheath is in effect a big earth rod, so its not as much of an issue compared to TNS supplied by split con.

 

[Andy™]

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.

thats part of the problem ADS....

if its presented as TNS, then it should be TNS all the way to star. but unfortunately they PME just about everything, so even if you have TNS, and you know its PME'd outside property, then working to 7671 you still have to treat it as TNS.

if its a lead cable, then you do have the advantage that the sheath is in effect a big earth rod, so its not as much of an issue compared to TNS supplied by split con.

 

[Larnacaman]

All becomes clear now ...lol!!! You have little to worry about with the supply you have at that portacabin. The hemodialysis equipment have numourous patient electrical safety devices incorporated within the machine. The only requirement they normally call for is a clean earth back to it's supply point and it's supply outlet protected by a 10 mA double pole RCD...

Now if we had been talking about Group 2 rooms, then that's a whole new ball game all together. But even then, your supplying earth system wouldn't of mattered a jot, .....as these rooms will be supplied by an isolating transformer and an IT earthing arrangement monitored by a line insulation monitoring device ( LIM ) Plus the numerous other requirements and restrictions for in and also around (general vicinity) group 2 rooms....

 

[Larnacaman]

All becomes clear now ...lol!!! You have little to worry about with the supply you have at that portacabin. The hemodialysis equipment have numourous patient electrical safety devices incorporated within the machine. The only requirement they normally call for is a clean earth back to it's supply point and it's supply outlet protected by a 10 mA double pole RCD...

Now if we had been talking about Group 2 rooms, then that's a whole new ball game all together. But even then, your supplying earth system wouldn't of mattered a jot, .....as these rooms will be supplied by an isolating transformer and an IT earthing arrangement monitored by a line insulation monitoring device ( LIM ) Plus the numerous other requirements and restrictions for in and also around (general vicinity) group 2 rooms....

 

[Sidewinder]

Larnacaman,

I am working closely with the Dialysis Techs anyway on this one, so they are clued up on the machines, they are not quite so clued up on the electrical installs and are following Manuf' guidance, which only calls for 30mA as does GN7 at the moment.

I'm staying clear of G2 areas!

I have been to the local trust dialysis tech's repair centre with them so I have an idea of what goes on in the machines as they asked me to get to understand the issues they have to be able to "partner" them in this work, they know I have a strong background in control systems, etc also so they realise that I can understand their bits too, plus they are hoping I can assist them in machine faults to a limited extent when I go to these installs even if it is (probably what I will limit it to for ins reasons) getting the correct error codes / messages for them to know what is wrong!

It is the "quality" of the earthing that I could not originally decide on.

We basically have a 16mm from the local db back to the NT-S earth point, probably the best we can get.

The only thing we could improve on is maybe the local supplementary bonding that is called for in GN7 at the moment, though I'm not going to push this until I have seenthe HTM's.

Plus a rod at either end of the supply cable for belt & braces, but I'm not going to push that either, I have not yet looked up 7430 either.

I hope you can understand now why I did not announce the use in my op as it would have perhaps scared a few people off, and after all the PIR is only to 7671:2008 at the moment.

However, I would be wrong not to comment on other possible problems.

Thanks again for all of you help everyone.

 

[Sidewinder]

Larnacaman,

I am working closely with the Dialysis Techs anyway on this one, so they are clued up on the machines, they are not quite so clued up on the electrical installs and are following Manuf' guidance, which only calls for 30mA as does GN7 at the moment.

I'm staying clear of G2 areas!

I have been to the local trust dialysis tech's repair centre with them so I have an idea of what goes on in the machines as they asked me to get to understand the issues they have to be able to "partner" them in this work, they know I have a strong background in control systems, etc also so they realise that I can understand their bits too, plus they are hoping I can assist them in machine faults to a limited extent when I go to these installs even if it is (probably what I will limit it to for ins reasons) getting the correct error codes / messages for them to know what is wrong!

It is the "quality" of the earthing that I could not originally decide on.

We basically have a 16mm from the local db back to the NT-S earth point, probably the best we can get.

The only thing we could improve on is maybe the local supplementary bonding that is called for in GN7 at the moment, though I'm not going to push this until I have seenthe HTM's.

Plus a rod at either end of the supply cable for belt & braces, but I'm not going to push that either, I have not yet looked up 7430 either.

I hope you can understand now why I did not announce the use in my op as it would have perhaps scared a few people off, and after all the PIR is only to 7671:2008 at the moment.

However, I would be wrong not to comment on other possible problems.

Thanks again for all of you help everyone.

 

[Larnacaman]

Yes ....perhaps your right as far as the 30mA trip is conserned, as i generally work to DIN/VDE standards on my hospital projects as far as Medical Rooms are conserned. They are recognised as the highest European medical standard...

Can't really see that roding is going to give you anything. even if there was a cable fault on the portacabins 16mm supply cable, that fault would also be transposed to the Rods too. Yes plenty of supplementary cross bonding in the portacabin itself, that goes without saying...lol!!!

Now, ...one thing that the Germans do with there earthing arrangements for medical rooms, is that they keep separate building, (re-bar, water pipe, medical gas pipes, etc etc....) and electrical earths. They bring back 16mm bonding cables from ALL extraneous earth points (PA) to a separate insulated earth bar at the main panel where it is linked to the electrical earth bar (PE) again insulated, via a short 16mm cable link. Makes fault finding very easy, among other useful aspects.

One thing you may or may not of realised is that, that portacabins construction is virtually a faraday cage with it's metal outer skin, and there-by should shield medical equipment within, from outside electrostatic etc, interferences....

Anyway, as i say i think you have very little to concern yourself about with this particular portacabins electrical supply. Sounds like a sound installation to me!!!

 

[Larnacaman]

Yes ....perhaps your right as far as the 30mA trip is conserned, as i generally work to DIN/VDE standards on my hospital projects as far as Medical Rooms are conserned. They are recognised as the highest European medical standard...

Can't really see that roding is going to give you anything. even if there was a cable fault on the portacabins 16mm supply cable, that fault would also be transposed to the Rods too. Yes plenty of supplementary cross bonding in the portacabin itself, that goes without saying...lol!!!

Now, ...one thing that the Germans do with there earthing arrangements for medical rooms, is that they keep separate building, (re-bar, water pipe, medical gas pipes, etc etc....) and electrical earths. They bring back 16mm bonding cables from ALL extraneous earth points (PA) to a separate insulated earth bar at the main panel where it is linked to the electrical earth bar (PE) again insulated, via a short 16mm cable link. Makes fault finding very easy, among other useful aspects.

One thing you may or may not of realised is that, that portacabins construction is virtually a faraday cage with it's metal outer skin, and there-by should shield medical equipment within, from outside electrostatic etc, interferences....

Anyway, as i say i think you have very little to concern yourself about with this particular portacabins electrical supply. Sounds like a sound installation to me!!!

 

[Sidewinder]

Canoeboy,

Nae bother really it just seemed like an odd thing to do to an opening post of a thread.

Totally forgiven, we all make mistakes part of being human and all that.

I still can't drive certain features of this forum software!

 

[Sidewinder]

Canoeboy,

Nae bother really it just seemed like an odd thing to do to an opening post of a thread.

Totally forgiven, we all make mistakes part of being human and all that.

I still can't drive certain features of this forum software!

 

[Voltimax]

Very sorry mateBit of a newbie mistake, L plates and all

Groan removed and a thanks for an interesting thread

Ya see why I didn't want you NAPIT louts following me here now?

Total embarrassment total :coat

ROTFWLROTFWLROTFWL

:slap

 

[Voltimax]

Very sorry mateBit of a newbie mistake, L plates and all

Groan removed and a thanks for an interesting thread

Ya see why I didn't want you NAPIT louts following me here now?

Total embarrassment total :coat

ROTFWLROTFWLROTFWL

:slap

 

[Sidewinder]

ROTFWLROTFWLROTFWL

 

[Sidewinder]

ROTFWLROTFWLROTFWL

 

[Voltimax]

Sorry Dave, I just couldn't resist:^O

Payback dontcha know ]

 

[Voltimax]

Sorry Dave, I just couldn't resist:^O

Payback dontcha know ]

 

[ProDave]

This is from 'Scottish Powers' - LOW VOLTAGE EARTHING POLICY ANDAPPLICATION 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:

• Separate neutral and earth conductor (SNE) bonded and earthed at or near the substation known as TN-S

• Combined neutral and earth conductors (CNE) earthed at several points(protective multiple earthing – PME), known as TN-C

• Combined neutral and earth conductor earthed adjacent to the customer’s supply terminals (protective neutral bonding – PNB – applies to a dedicated transformer supplying a single customer)

I'm currently wiring a new build, supplied (by Scottish Hydro) with an individual transformer and presented to the customer as PNB as described above.

What earthing arangement does that correspond to in 7671 speak? It's not TN-S, or TN-C i.e what earting arangement do I put on my certificate when it's finished?

 

[ProDave]

This is from 'Scottish Powers' - LOW VOLTAGE EARTHING POLICY ANDAPPLICATION 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:

• Separate neutral and earth conductor (SNE) bonded and earthed at or near the substation known as TN-S

• Combined neutral and earth conductors (CNE) earthed at several points(protective multiple earthing – PME), known as TN-C

• Combined neutral and earth conductor earthed adjacent to the customer’s supply terminals (protective neutral bonding – PNB – applies to a dedicated transformer supplying a single customer)

I'm currently wiring a new build, supplied (by Scottish Hydro) with an individual transformer and presented to the customer as PNB as described above.

What earthing arangement does that correspond to in 7671 speak? It's not TN-S, or TN-C i.e what earting arangement do I put on my certificate when it's finished?

 

[Andy™]

I'm currently wiring a new build, supplied (by Scottish Hydro) with an individual transformer and presented to the customer as PNB as described above.What earthing arangement does that correspond to in 7671 speak? It's not TN-S, or TN-C i.e what earting arangement do I put on my certificate when it's finished?

TNCS