Metal lamppost in garden... TNC-S

[weevilward]

Evening all,
Need some opinions on this one please:
TNC-S house, complete new install, all going to plan, nearly finished second fix, customer then arrives with a huge metal lamppost (bought from Frinton-on-sea promenade...) and wants it hooked up in the back garden.
What is the general consensus on this - my concern is: in the event of loss is supply neutral, everything connected to MET, including that lamppost, will rise to a voltage, anyone touches it may get a shock?
Or, will the fact it's planted in the earth keep any possible voltage down?
Am I making something out of nothing here or would this be safer as a TT?

Any thoughts welcome.

 

[westward10]

What is it with this neutral loss, in the house no one bothers but go outside and there are shouts of ROD IT.

 

[weevilward]

Ok, so touching a radiator bonded in the house in no different to touching a lamppost bonded in the garden? Is that what you're getting at?

 

[weevilward]

Ok, so touching a radiator bonded in the house in no different to touching a lamppost bonded in the garden? Is that what you're getting at?

 

[Flanders]

Im think there is somthing in special location for lamp post but it may be relating to street furniture

 

[Leesparkykent]

The post will propably act as one big rod.

 

[westward10]

Most lighting columns on the highway are PME they seem okay.

 

[weevilward]

So I'm reading too much into it.
Thanks fellas. Never thought twice about domestic outside lighting before, but when something different comes along it makes you think twice...

 

[Richard Burns]

This is probably a case of minimal risk. In general you are not constantly handling a lamppost, as opposed to hand held electrical equipment, and so the risk of neutral loss fault occurring and it being a risk due to contact are low.
Bonding will have limited effect since the potential you are trying to eliminate is between earth and the supply and bonding will only limit the PD between the MET and the supply.
Within a property there should be no potential differences because the bonding connects all sources of potential difference together. Outside a property without installing conductive mats in the ground you cannot avoid being in the presence of a nominal 0V from true earth and so the risk is increased.

 

[Paul mccullagh]

Run swa to the lamp post (volt drop calculations) bonded on a 30MA rcd in the consumer unit job done!

 

[westward10]

Run swa to the lamp post (volt drop calculations) bonded on a 30MA rcd in the consumer unit job done!

Why would it require rcd protection.

 

[westward10]

The post will propably act as one big rod.

This was suggested many years ago by the ILE but was felt the column would be unreliable as an electrode due to corrosion, protection on the column to prevent corrosion and the means of bedding it in the ground.

 

[weevilward]

Why would it require rcd protection.

It doesn't need RCD but it wouldn't hurt to have it.

This was suggested many years ago by the ILE but was felt the column would be unreliable as an electrode due to corrosion, protection on the column to prevent corrosion and the means of bedding it in the ground.

Yeah this one is pretty rusty!

 

[weevilward]

This is probably a case of minimal risk. In general you are not constantly handling a lamppost, as opposed to hand held electrical equipment, and so the risk of neutral loss fault occurring and it being a risk due to contact are low.
Bonding will have limited effect since the potential you are trying to eliminate is between earth and the supply and bonding will only limit the PD between the MET and the supply.
Within a property there should be no potential differences because the bonding connects all sources of potential difference together. Outside a property without installing conductive mats in the ground you cannot avoid being in the presence of a nominal 0V from true earth and so the risk is increased.

Thanks Richard, this makes sense.

 

[Paul mccullagh]

I would personally protect this with a rcd due to someone dismantling fixtures and changing a light bulb!