Wiring for a light/lantern on a brick pillar

[bricky48not]

Hello There, I have built the garden pillar with a hollow pipe going down inside and room for a metal clad box in the 'top' below the brick capping slab. The intention was to run a Steel Wire Armoured cable from the lights metal jb inside the pillar -around to my porch which will have a metal box inside the porch to terminate the swa cable with connector.
I have just managed to install (with great difficulty) a 13a socket inside the porch from the downstairs house ringmain.
My plan was to link a switched spur from the 13a skt and then connect to that a RCD ...but then didn't like the idea of 240v going to the wall from the RCD so thought about the sw' spur feeding a transformer supplying the pillar light (say 50v)) by the spur. What is the correct way to do this please?

 

[bernardgreen]

The answer depends on the wattage of the lamp and the length of the cable.

There is also the problem of how to earth the metal box in the pillar and that depends on what type of earth you have in the house. If it is a PME earth then it is not good practise to use the earth from inside the house to earth metal items outside the house as the "earth" inside the house may not be the same potential as true ground potential. Some one standing on true ground and touching the "earthed" metal box or the metal lamp may feel a tingle of mild electric shock or if there is a serious but not yet discover fault in the local supply network then that could be a very strong tingle and in extreme cases a shock that causes injury.

 

[ban-all-sheds]

Hello There, I have built the garden pillar with a hollow pipe going down inside and room for a metal clad box in the 'top' below the brick capping slab. The intention was to run a Steel Wire Armoured cable from the lights metal jb inside the pillar -around to my porch which will have a metal box inside the porch to terminate the swa cable with connector.

As per what bernard said, did you consider the issues surrounding exporting a PME earth, if that's what you have?

Did you apply for Building Regulations approval?

I have just managed to install (with great difficulty) a 13a socket inside the porch from the downstairs house ringmain.

If the porch doesn't have a door to the outside then that counts as installing an outside supply which is also notifiable.

My plan was to link a switched spur from the 13a skt and then connect to that a RCD

So the socket circuit doesn't already have an RCD? It was a contravention of the Wiring Regulations to add a socket, in that case, which is not a good thing when it comes to complying with P1.

What do you plan to use the socket for?

...but then didn't like the idea of 240v going to the wall from the RCD

Why on earth not?

so thought about the sw' spur feeding a transformer supplying the pillar light (say 50v)) by the spur.

50V lights are not easy to find, and I doubt you'd ever be able to get low energy lamps.

What is the correct way to do this please?

I would say, without doubt, that the correct way is to get an electrician. You really do seem out of your depth.

 

[Alarm]

BAS you pop up more than Virgin Media pop ups

 

[ban-all-sheds]

And I'm immune to all pop-up and script blockers.

 

[Alarm]

lol

 

[JohnW2]

And I'm immune to all pop-up and script blockers.

Are you sure? Doesn't

Untitled

• JohnW2
• 31 Aug 2011
• 2

. count as an effective pop-up blocker in this context?

Kind Regards, John.

 

[ban-all-sheds]

8)

 

[bricky48not]

Thanks for your comments Chaps, Yes the house has PME with a label on to prove it. The difficulty with installing a 13a socket in the porch (for the wife's Christmas tree) was that although it was to be sited two feet away from the 13a ringmain in the house, the concrete in the porch floor made it almost impossible -but I eventually managed to get the 2.5mm twin core + E through eventually. It is only a single (Radial) cable to this socket.
So because it is still part of the house ring main what is there still a problem with the RCD comments.
The porch does have it's own outside door.
For the pillar light, I really did not mean to mention the 50v lamp, becauseI had considered using an Energy efficient lamp if I was to use a Transformer -say 12v 36/60w output to the pillar light.
Yes I probably am out of my depth being retired for some time and not up to date like all you fella's with this task considering all the things you are highlighting to me, but when I asked 2 bonafide Electricians today about how they would carry it out (before seeing your replies on the computer) they both indicated that they would not use a Transformer.
They both suggested that they would link from the new 13a skt a RCCD fused (low value) Switch supplying the feed to the light on the pillar via a 3 x core 1.5mm SWA cable both braided at each end in a metal JB box.
One of the cores being the earth.
No mention of 'Exporting Earth's, Building Regulation Approval or PME's from those two!!)
Just to clarify it's only a 14m run to the pillar.
Thanks again, unless you can suggest how to do it properly

 

[bernardgreen]

The exported earth is the hazard. It is safe provided the potential of the PME earth in the house is within a few volts of true ground. It is for most of the time but in the event of a fault in the local distribution network the earth can raise to a very high potential. Even then inside the house, the equipotential zone, it is a low risk. But outside the house the "earthed" items will give a shock to any one touching them while in contact with the ground.

If the lamp you use is double insulated and at least IP44 ( water proof to a limited degree but safe in falling rain ) then you do not need the exported earth at the pillar. Yes having no earth makes it safer. (according to the "guidelines" ) You still need the earth on the armour of the cable to protect some one cutting the cable with a spade. ( though this again an exported earth when the spade hits it.)

So replace the metal box in the pillar with a plastic one and ensure that end of the armour cannot make contact with anything in the pillar and it should be safe.

If there is any risk of the lamp getting a jet of water from a hose pipe then you might need a higher IP rating for the lamp.

 

[studentspark]

Please correct me but,thats not right is it.

This exporting the earth.

There is nothing wrong taking the PME earth to a garage with no extraneous conductive parts.

You could have metal clad sockets. whats the difference, between that and the pillar light

What you can't have is two earthing types.

So the suggestion would be that each light would needs its own rod. Clearly not.

 

[JohnW2]

Please correct me but,thats not right is it. This exporting the earth. There is nothing wrong taking the PME earth to a garage with no extraneous conductive parts. You could have metal clad sockets ...

You have to think more widely that just extraneous-conductive-parts in the usual sense, particularly for outbuildings such as sheds. If, as will often be the case, the shed/garage has a metaclad switch just inside the door which can be touched whilst one is still standing on wet soil outside of the building, then there is a potential problem with exported TN-C-S. Even inside the shed/whatever, the floor itself may be damp and therefore a route to true earth, hence again a potential problem. The problem is that one obviously cannot effectively bond either a lawn or a building's wet floor..

What you can't have is two earthing types. So the suggestion would be that each light would needs its own rod. Clearly not.

I'm not sure what you mean here. Provided you did not also connect the installation's earth, you can use earth rods for anything you wish (provided all the protection/disconnection etc. requirements are met).

Kind Regards, John.

 

[studentspark]

If the supply earth is at the potential of the earth at the transformer
Why would the earth at the shed be that much different.
If I am correct they are multiple earthing points along the combined N-E length, which will be near the property in question.

If they was a fault with the neutral, would it not cause issue with all exposed parts?

 

[JohnW2]

If the supply earth is at the potential of the earth at the transformer
Why would the earth at the shed be that much different.
If I am correct they are multiple earthing points along the combined N-E length, which will be near the property in question.
If they was a fault with the neutral, would it not cause issue with all exposed parts?

As you point out in your final comment, the safety concerns arise if there is a supply-side neutral fault in a 'bad' place. Under those circumnstances, the potential of the incoming neutral (hence the PME 'earth', and all the CPCs of the installation) can rise to considerably above true earth potential. If the installation has been undertaken correctly, that shouldn't be a problem indoors, since all exposed-conductive-parts and extrinsic-conductive-parts should be effectively bonded togetehr - hence significant potential differences cannot exist between them, even if they are all a potential consierably above that of true earth. The moment you 'export' the installation's 'earth' outdoors, where there are inevitable paths to true earth all around, the high potential 'earth' of the installation can become a serious hazard.

Kind Regards, John.

 

[studentspark]

I do understand the risk.Is it more theoretical though?

If it was so dangerous how come they are no (to my limited knowledge)
regs or best practice guidelines on this