PME

[wazzer]

Hello first time on
looking for a bit of advice
I was at a dwelling pricing new consumer unit install in house
When i noticed a container connected to PME
In the house is main consumer unit and connection for container is fed seperatly
The container is fed seperatly by Henley block 16 mm tails to a lewd en box 80 amp fuse and 100 main amp isolation switch
Feed to container is 16 mm armored swa
On checking in container their is a consumer unit with main isolating switch and 63 amp type ac rcd covering 1 no 32 amp wring and 1 no 6 amp lighting circuit
All accessories are plastic
Main earthing terminal is earthed by armored cable earth cable and consumer unit and container connected to it
I do not have much experience in TT installs
Would changing this to tt on container and putting a type s Rcd 100 time delayed at where the connection is in house instead of lewd en cut out switch is be correct way to make this comply
regards

 

[Fleeting]

It's fine as it is. If main protective bonds are used in the container then the supply cpc must be able to support it, fine if the supply cable uses a core as the cpc.

 

[ProDave]

I thought a container was treated as any other metal clad "building" like a caravan and prohibited from connection to a PME earth. I would also be inclined to convert it to a local TT earth.

 

[Fleeting]

Why would you make it TT?

 

[ProDave]

Same reason as you do a caravan, in case of a PEN fault.

 

[Fleeting]

It isn't a caravan.

 

[ProDave]

It isn't a caravan.

But it IS a metal "building" that is in all probability just sat on the ground and not attached to proper foundations, so in the event of the suppliers combine Neutral and Earth connector going open circuit, the "earth" which is bonded to the metal container can float up to L potential, with exactly the same consequences as when that happens with a caravan and why caravans are prohibited from connection to a PME eatth.

If you are happy with the potential consequences (see what I did there) carry on, but my name would not be on the IEC for that.

 

[binky]

Why would you make it TT?

To avoid 'exporting earth' outside of equipotential zone of the house.

 

[Fleeting]

To avoid 'exporting earth' outside of equipotential zone of the house.

Equipotential zone is a defunct term with regard to BS7671 and in reference to the container there is no requirement to provide an alternative earthing system.

 

[ProDave]

Equipotential zone is a defunct term with regard to BS7671 and in reference to the container there is no requirement to provide an alternative earthing system.

Like I say, it may not explicitely be prohibited like caravans, but you put your name on the EIC if you want to and carry the can if it goes tits up. I won't.

 

[Phoenix]

Would changing this to tt on container and putting a type s Rcd 100 time delayed at where the connection is in house instead of lewd en cut out switch is be correct way to make this comply
regards

Remember that you still need overcurrent protetcion, so you can't change out the switchfuse for an RCD, you need to add it in addition, chances are the easiest way is to see if lewden do a time day RCD to replace the main switch in the switchfuse.

But, if this is completely separate from the board you are changing, then there is no requirement for you to do anything other than note your concerns in comments on existing installation

 

[binky]

Equipotential zone is a defunct term with regard to BS7671 and in reference to the container there is no requirement to provide an alternative earthing system.

So it's safe to export the earth? Couldn't give a toss about terms, safety is the issue.

 

[Fleeting]

So it's safe to export the earth? Couldn't give a toss about terms, safety is the issue.

You aren't exporting anything there is no boundary in general terms as to where a cpc cannot be taken.

 

[binky]

You aren't exporting anything there is no boundary in general terms as to where a cpc cannot be taken.

It certainly used to be 'no no' is previous versions of the regs, taking the cpc out of the main building was only allowed by permission from DNO on a PME system. So, I know we have discussed this before, but are you saying BS 7671 has been changed to allow this? It's fair to say since retiring I havn't kept up to date with everything that has changed, but I do regard this as potentially dangerous as per ProDave post above.

 

[Fleeting]

It certainly used to be 'no no' is previous versions of the regs, taking the cpc out of the main building was only allowed by permission from DNO on a PME system. So, I know we have discussed this before, but are you saying BS 7671 has been changed to allow this? It's fair to say since retiring I havn't kept up to date with everything that has changed, but I do regard this as potentially dangerous as per ProDave post above.

I started work under the 15th Ed and a quick perusal gives no indication that permission was required to take a cpc outside of a building.

 

[Steviesparkie]

I thought a container was treated as any other metal clad "building" like a caravan and prohibited from connection to a PME earth. I would also be inclined to convert it to a local TT earth.

See reg 411.3.3 only refers to inside a building.no mention of an external part.
I would be inclined to check it is connected to earth and leave it as is.

 

[binky]

I started work under the 15th Ed and a quick perusal gives no indication that permission was required to take a cpc outside of a building.

only on PME and it was definetly a 'thing' 16th edition I think. I pointed this out to some sparkies on a job one day - I was doing solar, they were rewiring things and installing a supply to an outbuilding being conveted to an office. They had a look that evening, concluded I was right, and TTd the outbuilding.

 

[Fleeting]

only on PME and it was definetly a 'thing' 16th edition I think. I pointed this out to some sparkies on a job one day - I was doing solar, they were rewiring things and installing a supply to an outbuilding being conveted to an office. They had a look that evening, concluded I was right, and TTd the outbuilding.

I have flicked through my 16th Eds and from what I can see there is nothing to suggest this is correct.

 

[binky]

I have flicked through my 16th Eds and from what I can see there is nothing to suggest this is correct.

thought you were a long time replying

 

[apprentice87]

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..