What's the deal with not being permitted to connected caravan pitch sockets' protective conductors, for example, to the PEN supply?
Same for fairgrounds, marinas, etc.
Same for fairgrounds, marinas, etc.
TN-C-S and Special Locations
- Thread starter SgtTrojan
- Start date
You are prohibited from using a PME earth on caravan pitches under BS7671 and ESQCR. (There are other installation situations where it is prohibited/not recommended as well)
It is because of the difficulty in achieving an equipotential zone in that situation and the increased dangers involved in the possible 'broken Neutral' scenario. (Think of all that metalwork and somebody standing barefooted on wet grass !)
It is because of the difficulty in achieving an equipotential zone in that situation and the increased dangers involved in the possible 'broken Neutral' scenario. (Think of all that metalwork and somebody standing barefooted on wet grass !)
The restrictions on a PEN conductor though, having to be a split concentric cable, making a broken neutral being virtually impossible. Wouldn't thte best situation be provided by a direct connection to the suppliers facility?
But if there arrangement is TN-S then it is permitted to connect direct to it.
I still don't get it.
But if there arrangement is TN-S then it is permitted to connect direct to it.
I still don't get it.
It is a bit pointless to use split concentric cable for a TN-CS supply, more likely to use concentric cable.
It is possible to have a break in a PEN, just as it is in any conductor wether it be from mechanical damage, loose connection etc. In a TN-CS PME system there is extra connections with earth provided by the supplier along the systems length to minimise the rise in potential (wrt mother earth) of the exposed metalwork of any connected equipment in the event of a broken combined neutral and earth.
The risk is judged too high to be used for caravan site hookups and marinas, hence is illegal to do so.
Split concentric can be used for TN-S, it is OK to use TN-S for caravan site hookups etc.
Where the supply is TN-CS you'd need to drive an earth spike in and convert it to a TT system i.e. not use the suppliers earth.
It is possible to have a break in a PEN, just as it is in any conductor wether it be from mechanical damage, loose connection etc. In a TN-CS PME system there is extra connections with earth provided by the supplier along the systems length to minimise the rise in potential (wrt mother earth) of the exposed metalwork of any connected equipment in the event of a broken combined neutral and earth.
The risk is judged too high to be used for caravan site hookups and marinas, hence is illegal to do so.
Split concentric can be used for TN-S, it is OK to use TN-S for caravan site hookups etc.
Where the supply is TN-CS you'd need to drive an earth spike in and convert it to a TT system i.e. not use the suppliers earth.
Apologies. Concentric
http://www.diynot.com/wiki/electric...bles_straight_concentric_and_split_concentric
From our very own wiki.
So, because in the extremely unlikely event that the entire neutral concentric conductors are all broken, and the distributors CPD device does not operate this is added as a statutory requirement? I thought the idea of concentric cable was that it is virtually impossible to break the PEN conductor without causing the CPD to operate, hence why some people call it "Thief proof cable" to stop people stealing electricity?
http://www.diynot.com/wiki/electric...bles_straight_concentric_and_split_concentric
From our very own wiki.
So, because in the extremely unlikely event that the entire neutral concentric conductors are all broken, and the distributors CPD device does not operate this is added as a statutory requirement? I thought the idea of concentric cable was that it is virtually impossible to break the PEN conductor without causing the CPD to operate, hence why some people call it "Thief proof cable" to stop people stealing electricity?
?
Remove a section of the outer sheath and carefully snip through the PEN strands one at a time with the tips of a pair of small, sharp cutters?
Yeah, but that is a deliberate act of vandalism and I'm sure you would agree that it is a lot easier to steal a separate protective conductor leaving the installation condition in the same situation?
Why would someone wanting to steal either electricity (or conductors) worry about deliberate acts of vandalism?
They wouldn't but the thing I am not grasping is:
The logic seems to be that connecting the protective conductor of the caravan sockets to the PEN conductor is breaking statutory law because the PEN conductor might be broken.
So why is connecting to a TN-S system any better when the seperate CPC can be broken (or stolen) even easier?
The logic seems to be that connecting the protective conductor of the caravan sockets to the PEN conductor is breaking statutory law because the PEN conductor might be broken.
So why is connecting to a TN-S system any better when the seperate CPC can be broken (or stolen) even easier?
A broken suppliers earth in a TN-S will not on it's own render the chassis of a caravan live.
A broken PEN (remember the conductor is also being used as a neutral) will pull the voltage on the chassis of the caravan towards one of the phase voltages, the voltage depending on loading on the system.
A broken PEN (remember the conductor is also being used as a neutral) will pull the voltage on the chassis of the caravan towards one of the phase voltages, the voltage depending on loading on the system.
OK, so where there is no return path or zero potential the potential difference of the line supply will pass through, say, a lamp filament and through the caravan neutral bar. So 230v on the neutral bar. This in itself is bad, agreed.
Do caravan installations connect the structure to neutral similar to the car electrics principle of grounding to zero?
Do caravan installations connect the structure to neutral similar to the car electrics principle of grounding to zero?
I had to look this one up
Problem is that the site owner has no control over the quality of the lead between caravan / mobile home / etc and the socket in the post that supllies the pitch with power. For all the owner knows the lead has no earth and the live and neutral are reversed.
So the requirment to ensure the caravan is safe for occupants and passers by has to be "local" to the caravan and that is best achieved by having a TT type supply and earthing the caravan and all its exposed metal to the ground with a ground spike. The site owner can provide the earth spike as a convenience to the caravan owner but it must be a ground rod of adequately low impedance.
Problem is that the site owner has no control over the quality of the lead between caravan / mobile home / etc and the socket in the post that supllies the pitch with power. For all the owner knows the lead has no earth and the live and neutral are reversed.
So the requirment to ensure the caravan is safe for occupants and passers by has to be "local" to the caravan and that is best achieved by having a TT type supply and earthing the caravan and all its exposed metal to the ground with a ground spike. The site owner can provide the earth spike as a convenience to the caravan owner but it must be a ground rod of adequately low impedance.
Which makes sense with regard to boats in marinas and rides and stalls and such in fairgrounds. The mobile equipment used in such installations cannot be verified for safety.
Thanks dudes.
Thanks dudes.
Even when using a concentric cable there is still a single point where it can (and does) fail.....where this concentric is grouped and crimped to the supply or indeed the service head. Also further back the supply as not all neutral points are earthed down.
A caravan connected to a PME supply could end up with upto 240v present on the metal chassis in the event of a neutral loss, and with someone standing on the grass and grasping a handrail or door handle, this would not be good!
Lost neutrals DO occur - most sparks who actually work an 8hr, 5day week will see this more often then you think!
A caravan connected to a PME supply could end up with upto 240v present on the metal chassis in the event of a neutral loss, and with someone standing on the grass and grasping a handrail or door handle, this would not be good!
Lost neutrals DO occur - most sparks who actually work an 8hr, 5day week will see this more often then you think!
In Devon?? As if 
Thats where Arthur served his apprenticeship
Arfur Day
Thats where Arthur served his apprenticeship
Arfur Day
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