Permanent metal building

[phase2]

Permanent small single storey prefab metal office on concrete base. Has metal feeder pillar adjacent for supply (tncs) . The feeder pillar has 32 amp mcb and switch. A person can touch both metal building and feeder pillar at the same time as its only 30cm from building.

The building comes with 32 amp female commando socket externally which feeds small rcbo consumer unit inside building. Inside walls are sheeted with boarding and floors are timber with carpet. Inside a few sockets, lighting and aircon unit.

A male commando socket with 6mm flex has been left to finnish the connection. Length of cable is 2m .

As its a permanent structure then a tncs supply can still be used?
The cable as is flex will require an upstream rcd in the feeder pillar?
Thanks for any info.

 

[EricMark]

As its a permanent structure then a tncs supply can still be used?

Can it, seem to remember reading rules have changed, and many static caravans now are not permitted to have a TN-C-S supply.

Forgetting the rule book, we are looking at the equipotential zone, if you can cross between zones without touching any earthed metal as when walking through a front door in a normal house, which may have a metal front door, but it is not earthed to the frame of the building, then there is no risk, but if the building is metal, so it will be earthed by something somewhere, then the building needs to be at ground potential.

If we are looking at a building like where I work, where the steel work is into the ground, in fact it is bonded to the railway tracks which go for 8 miles, even if there is a fault, it is unlikely to raise the bonded voltage by much, so even if it does not comply, it is unlikely to cause a problem.

I personally don't think the building I work in does comply, as it has at least 3 maybe more, supplies, and so it links multi TN-C-S earths together, main problem is the air line, not found an earth break in the airline, which joins two buildings together which are supplied from different step down transformers.

But to isolate the two buildings with railway track also between the buildings would be near impossible. But in theory this could overload the PEN.

In your case, think you need a TN-S or TT supply, don't think you can use a TN-C-S supply.

 

[PS Electrics]

Permanent small single storey prefab metal office on concrete base. Has metal feeder pillar adjacent for supply (tncs) . The feeder pillar has 32 amp mcb and switch. A person can touch both metal building and feeder pillar at the same time as its only 30cm from building.

The building comes with 32 amp female commando socket externally which feeds small rcbo consumer unit inside building. Inside walls are sheeted with boarding and floors are timber with carpet. Inside a few sockets, lighting and aircon unit.

A male commando socket with 6mm flex has been left to finnish the connection. Length of cable is 2m .

As its a permanent structure then a tncs supply can still be used?
The cable as is flex will require an upstream rcd in the feeder pillar?
Thanks for any info.

Some observations

When you say permanent is that your definition? The way this is to be installed does not fit with this being a permanent building. There could be some implications if this is temporary (don't have my regs book to hand). Definition of temporary can be debated though, only the original designer of this will know the answer.

Are you sure it is a female commando socket feeding the DB? The male commando pins would be live? It should be a 32A IP67 Appliance Inlet on the building. I would expect a female socket at the pillar and then a short lead between the two. Not a fan of a hard wired floating commando lead to be honest if that is what you described?

There maybe an upstream RCD to the feeder pillar? If not then yes.

Being a metal building on a TNC-S would have implications if the metal building or the metal feeder pillar are Extraneous Conductive parts.

Is this something you have been asked to look at?

 

[phase2]

Can it, seem to remember reading rules have changed, and many static caravans now are not permitted to have a TN-C-S supply.

Forgetting the rule book, we are looking at the equipotential zone, if you can cross between zones without touching any earthed metal as when walking through a front door in a normal house, which may have a metal front door, but it is not earthed to the frame of the building, then there is no risk, but if the building is metal, so it will be earthed by something somewhere, then the building needs to be at ground potential.

If we are looking at a building like where I work, where the steel work is into the ground, in fact it is bonded to the railway tracks which go for 8 miles, even if there is a fault, it is unlikely to raise the bonded voltage by much, so even if it does not comply, it is unlikely to cause a problem.

I personally don't think the building I work in does comply, as it has at least 3 maybe more, supplies, and so it links multi TN-C-S earths together, main problem is the air line, not found an earth break in the airline, which joins two buildings together which are supplied from different step down transformers.

But to isolate the two buildings with railway track also between the buildings would be near impossible. But in theory this could overload the PEN.

In your case, think you need a TN-S or TT supply, don't think you can use a TN-C-S supply.

Thank you for your answer

 

[westward10]

Can it, seem to remember reading rules have changed, and many static caravans now are not permitted to have a TN-C-S supply.

Forgetting the rule book, we are looking at the equipotential zone, if you can cross between zones without touching any earthed metal as when walking through a front door in a normal house, which may have a metal front door, but it is not earthed to the frame of the building, then there is no risk, but if the building is metal, so it will be earthed by something somewhere, then the building needs to be at ground potential.

If we are looking at a building like where I work, where the steel work is into the ground, in fact it is bonded to the railway tracks which go for 8 miles, even if there is a fault, it is unlikely to raise the bonded voltage by much, so even if it does not comply, it is unlikely to cause a problem.

I personally don't think the building I work in does comply, as it has at least 3 maybe more, supplies, and so it links multi TN-C-S earths together, main problem is the air line, not found an earth break in the airline, which joins two buildings together which are supplied from different step down transformers.

But to isolate the two buildings with railway track also between the buildings would be near impossible. But in theory this could overload the PEN.

In your case, think you need a TN-S or TT supply, don't think you can use a TN-C-S supply.

Equipotential zone is a term not used anymore there are no zones to be crossed.

 

[mainline]

Permanent small single storey prefab metal office on concrete base. Has metal feeder pillar adjacent for supply (tncs) . The feeder pillar has 32 amp mcb and switch. A person can touch both metal building and feeder pillar at the same time as its only 30cm from building.

The building comes with 32 amp female commando socket externally which feeds small rcbo consumer unit inside building. Inside walls are sheeted with boarding and floors are timber with carpet. Inside a few sockets, lighting and aircon unit.

A male commando socket with 6mm flex has been left to finnish the connection. Length of cable is 2m .

As its a permanent structure then a tncs supply can still be used?
The cable as is flex will require an upstream rcd in the feeder pillar?
Thanks for any info.

Have you done any measurements of the building's steel work.

I would make it a TT.

How long is the run in flex ? Can you not use armoured.

 

[westward10]

The 32A socket should have 30ma RCD protection.
The fact you have a flexible cable does not dictate whether it needs RCD protection. You haven't stated what type of cable it is.
The fact you have a metal building and a TN-C-S supply is not relevant.
The only time there would be a hazard between the pillar and the building is if the metalwork is extraneous and is not effectively bonded to the pillar whether it is plugged in or not.

 

[phase2]

Not the actual building but similar. Supply is fed directly from abc box on wooden pole to feeder pillar .

 

[westward10]

Personally I would be hard wiring it. If main protective bonding is required then you have to consider whether the cpc to the socket can support it.
I see you are a trainee how are you involved with this?

 

[phase2]

Personally I would be hard wiring it. If main protective bonding is required then you have to consider whether the cpc to the socket can support it.
I see you are a trainee how are you involved with this?

Not a trainee . Jib grade senior electrician. Site is spammy on phone probable pressed something incorrect. Yes I agree it would have been much better to run armoured but not what the developer currently offered. Probably will do this but was interested in seeing the answers and as can be seen many varied thoughts on the subject. Thank you

 

[westward10]

Have you tested the metalwork to see if it is extraneous or if it is actually bonded to the earth terminal of the consumer unit?