PME

[Fleeting]

Only a loony would connect a metal container to TNCS. There is a reason that this must not be done with a caravan.

If anyone wants to stand in a coroners court being asked; "a caravan must not be connected to TNCS, can you explain to the court why you think this might be" they are welcome to..

It appears common sense is not so common..

john..

Tell me in BS7671 where this is prohibited.

 

[binky]

Recommendations from Stroma, as per most things another grey area, but sums up our differences of opinion quite nicely.

https://professional-electrician.com/technical/stroma-certification-supply-chain/

 

[Fleeting]

It isn't really a grey area and if it was considered such a risk it would be included in BS7671. I doubt any DNO can forbid a general installation having a remote supply from a PME system.

 

[binky]

It isn't really a grey area and if it was considered such a risk it would be included in BS7671. I doubt any DNO can forbid a general installation having a remote supply from a PME system.

it's only a risk in the event of failure of PEN conductor, and that doesn't happen often, and then someone has to be touching two surfaces with different voltage potentials, which isn't that likely either, yet we bond houses to keep touch voltages below 50V in the event of a fault. How often is someone touching two different conductive surfaces whilst a rewirable fuse takes 5s to blow in a house?

I would say risk is minimal, but not impossible, ergo for the sake of an earth rod in a metal outbuilding, I think that is a far safer option. Wooden shed, I would be far less concerned, but would still TT it.

 

[apprentice87]

Tell me in BS7671 where this is prohibited.

No problem at all..

It is prohibited [or was] in section 708...

Then we have the; "The Electricity Safety, Quality and Continuity Regulations 2002" which state;

Protective multiple earthing

9.—(1) This regulation applies to distributors' low voltage networks in which the neutral and protective functions are combined.

(2) In addition to the neutral with earth connection required under regulation 8(3)(b) a distributor shall ensure that the supply neutral conductor is connected with earth at—

(a)a point no closer to the distributor’s source of voltage (as measured along the distributing main) than the junction between that distributing main and the service line which is most remote from the source; and

(b)such other points as may be necessary to prevent, so far as is reasonably practicable, the risk of danger arising from the supply neutral conductor becoming open circuit.

(3) Paragraph (2)(a) shall only apply where the supply neutral conductor of the service line referred to in paragraph (2)(a) is connected to the protective conductor of a consumer’s installation.

(4) The distributor shall not connect his combined neutral and protective conductor to any metalwork in a caravan or boat..


john..

 

[Fleeting]

No problem at all..

It is prohibited [or was] in section 708...

Then we have the; "The Electricity Safety, Quality and Continuity Regulations 2002" which state;

Protective multiple earthing

9.—(1) This regulation applies to distributors' low voltage networks in which the neutral and protective functions are combined.

(2) In addition to the neutral with earth connection required under regulation 8(3)(b) a distributor shall ensure that the supply neutral conductor is connected with earth at—

(a)a point no closer to the distributor’s source of voltage (as measured along the distributing main) than the junction between that distributing main and the service line which is most remote from the source; and

(b)such other points as may be necessary to prevent, so far as is reasonably practicable, the risk of danger arising from the supply neutral conductor becoming open circuit.

(3) Paragraph (2)(a) shall only apply where the supply neutral conductor of the service line referred to in paragraph (2)(a) is connected to the protective conductor of a consumer’s installation.

(4) The distributor shall not connect his combined neutral and protective conductor to any metalwork in a caravan or boat..


john..

It isn't a caravan or boat.

 

[binky]

It isn't a caravan or boat.

No, it's a full metal box sitting on the ground, worse than the average caravan.

 

[Fleeting]

No, it's a full metal box sitting on the ground, worse than the average caravan.

Probably safer in that case.

 

[binky]

Probably safer in that case.

 

[Fleeting]

Consider the caravan, rubber tyres and some struts with the struts it's connection to ground. Steel container very weighty and a large surface area in connection to the ground. Which one is most dangerous with regard to true ground potential.

 

[ProDave]

Consider the caravan, rubber tyres and some struts with the struts it's connection to ground. Steel container very weighty and a large surface area in connection to the ground. Which one is most dangerous with regard to true ground potential.

Most containers I have seen sit on just a few paving slabs. Tell me the earth impedance of a metal box stood on a number of dry concrete paving slabs, and then in the event of a combined neutral earth conductor failure, how much the potential of the "earthed" metal box might rise in relation to the person standing on the ground next to it about to touch it.

It is no good imho saying it is not explicitly banned like a "caravan" so it is okay to ignore the potential issues.

Remember the caravan act sets out the legal definition of a "caravan" and in point of fact a "caravan" does not need to be on wheels to qualify. A portable building that can be moved by lifting with a crane and just sits on basic supports (i.e. a container) fits the legal definition of a "caravan"

If you fancy your chances in court in the unlikely event of that PEN fault occurring then carry on. Some of us will recognise the potential problems and not do it.

 

[Fleeting]

Most containers I have seen sit on just a few paving slabs. Tell me the earth impedance of a metal box stood on a number of dry concrete paving slabs, and then in the event of a combined neutral earth conductor failure, how much the potential of the "earthed" metal box might rise in relation to the person standing on the ground next to it about to touch it.

It is no good imho saying it is not explicitly banned like a "caravan" so it is okay to ignore the potential issues.

Remember the caravan act sets out the legal definition of a "caravan" and in point of fact a "caravan" does not need to be on wheels to qualify. A portable building that can be moved by lifting with a crane and just sits on basic supports (i.e. a container) fits the legal definition of a "caravan"

If you fancy your chances in court in the unlikely event of that PEN fault occurring then carry on. Some of us will recognise the potential problems and not do it.

Of course I recognise the potential danger and if someone wants to put in place a TT system for a container then crack on with it. The point of this thread was a container connected to a PME system and whether it should be TT, as current Regulations stand there is no requirement and never has been to do so. This container is not a caravan.

 

[binky]

Of course I recognise the potential danger and if someone wants to put in place a TT system for a container then crack on with it. The point of this thread was a container connected to a PME system and whether it should be TT, as current Regulations stand there is no requirement and never has been to do so. This container is not a caravan.

If you recognise the potential danger, then whether or not it's a caravan is irrelevant.

Incidentally, most caravans are grp and wood construction on a metal supporting chassis and lined with lots of plywood, plastics etc to make them warm and comfortable. So basically lacking electrically conductive surfaces internally, far safer than a steel container. My motorhome, which I'm currently sat in drinking wine, is not a caravan either, yet the site I'm on does not diffentiate between the 2 for the electrical supply and I would be very angry if they did for not providing a safe electrical hookup.

 

[Fleeting]

If you recognise the potential danger, then whether or not it's a caravan is irrelevant.

Incidentally, most caravans are grp and wood construction on a metal supporting chassis and lined with lots of plywood, plastics etc to make them warm and comfortable. So basically lacking electrically conductive surfaces internally, far safer than a steel container. My motorhome, which I'm currently sat in drinking wine, is not a caravan either, yet the site I'm on does not diffentiate between the 2 for the electrical supply and I would be very angry if they did for not providing a safe electrical hookup.

I follow Regulations and sleep soundly at night. In #2 I correctly answered the OP's question and nobody has provided substantiated evidence to question this.

 

[binky]

I follow Regulations and sleep soundly at night. In #2 I correctly answered the OP's question and nobody has provided substantiated evidence to question this.

In the words of Spock " illogical captain".

It was a similar discussion we had in regards to sharing RCDs with solar inverters. We concluded that is potentially dangerous several years before the regs caught up. And that was in the days before Sidewinder died, removing our direct input into IET. Containers are relatively new, and not as common as solar, so despite not being mentioned directly in the regs, if it's potentially lethal, in a way any well trained electrician can understand, it's still dangerous. Add to that guidance from registration bodies that also backs this up, which again, any well versed professional electrician should be aware of, and you are very welcome to your day in court.

 

[Fleeting]

Solar is not my bag of sweets but I respect your and others perspective on it. The electrifying of steel containers has been going on for decades, I remember doing some on Avonmouth docks in the early 90s. I understand the issue with an open PEN but BS7671 in general terms does not require you to compensate for this and should I be involved in an incident with an open PEN where I have followed Regulations and not "compensated" then the chances of me ending up in court is zero. Why, because the open PEN fault is outside my scope of responsibility and it is that simple.

 

[SPECIAL LOCATION]

It is no good imho saying it is not explicitly banned like a "caravan" so it is okay to ignore the potential issues.

Remember the caravan act sets out the legal definition of a "caravan" and in point of fact a "caravan" does not need to be on wheels to qualify. A portable building that can be moved by lifting with a crane and just sits on basic supports (i.e. a container) fits the legal definition of a "caravan"

A Caravan.. by definition of BS7671.. (regs wot we work to)..

IS actually a trailer leisure accommodation vehicle, used for touring.. designed to meet the requirements for the construction and use of road vehicles.. Similar reference is made to Motor Caravans & Leisure accommodation vehicles..

If when we say container.. We mean a typical shipping container.. (Maybe with some lights & power put into it)...
I cannot see how that could ever be considered a Caravan, Motor Caravan, Leisure accommodation vehicle or Boat...?
Nor is it on a Campsite or Marina...?
(708 relates to campsites.. not the bods and accommodation types that are using them, caravan, camper, tent etc..)

So any regulations specific to these "Special Locations" do not apply.

However.. If anyone did have any concerns about faults relating to losing an earthing connection external to the property..
Regulation 411.4.2 has noted that with TN installations an addition earth point such as by a rod could be added at the origin of the installation..

That has been a 'Note' since 17th ed Red book.... 2008
Or in the current (brown) book it is actually a Recommendation {third paragraph}!
I think this is more to do with passing the buck from the DNO's to provide a reliable earth connection!
but I may be wrong???

 

[binky]

Solar is not my bag of sweets but I respect your and others perspective on it. The electrifying of steel containers has been going on for decades, I remember doing some on Avonmouth docks in the early 90s. I understand the issue with an open PEN but BS7671 in general terms does not require you to compensate for this and should I be involved in an incident with an open PEN where I have followed Regulations and not "compensated" then the chances of me ending up in court is zero. Why, because the open PEN fault is outside my scope of responsibility and it is that simple.

So you would happily give someone advice that may kill someone, than advice that ensures a far safer installation. Makes no sense to me.

 

[Fleeting]

So you would happily give someone advice that may kill someone, than advice that ensures a far safer installation. Makes no sense to me.

As I said I would install to the requirements of the Regulations. There has been much said in this thread about you can't do this, the DNO won't permit that, exporting this that and the other but none of it has been substantiated.
If people want to put in place a TT system that is their perogative but the OP asked a question and my answer is correct according to BS7671.