Earthing of outdoor lighting

[macadonald]

Hi Guys,

I am wiring up some garden lighting. The lighting are a series of 6 bollard style aluminium lights set on hard wood timber bases in the flower beds. I have a dedicated feed from the dis board to an outside point and armoured cable with junction boxes screwed to the fence at each light.

What I'm a little unsure of is the earthing requirements. Each light simply has connectors for live, neatral and earth (no transformers). The feed from the dis board also has the earth. Can I assume that the earthing can be carried right back to the dis board rather than needing to earth each and every light?

What I could do if necessary is earth at the first junction box onto the brick work of the house, but not sure if this is necessary?

Any advise would be most welcome.

Ta

Maca

 

[chris765]

Are the lights class 2 (double insulated)? They may say class 2 or there may be a symbol which is a square inside a square?

are you running SWA between each junction box?
what sort of junction boxes are you using?
are you using 2 core SWA?

 

[PrenticeBoyofDerry]

If the light units are class II/double insulated type, look for this symbol:

Untitled

• PrenticeBoyofDerry
• 25 Feb 2011
• 14

or read the instruction that came with the product, as it maybe that they are not to be earthed.
It would be wise though to at least keep earth/cpc continuity throughout this circuit, even if this is not directly connected to the light fitting.
Have you got a link to the units you have bought or some brand, model details?

 

[bernardgreen]

The hazard is when a faulty lamp or cable leaves the case of the lamp live in close proximity to the wet soil.

Each light simply has connectors for live, neatral and earth

Which suggests they are NOT double insulated and DO require an earth. That said I would never trust double insulation in a wet garden environment and would be very carefull about the supply and earthing.

I earthed the two bollard lamps in my garden to their own earth rods and fed them via an isolation transformer. ( This partly because the garden was subject to flooding from a stream. )

 

[PrenticeBoyofDerry]

What I'm a little unsure of is the earthing requirements. Each light simply has connectors for live, neatral and earth (no transformers). The feed from the dis board also has the earth. Can I assume that the earthing can be carried right back to the dis board rather than needing to earth each and every light?

Okay I somehow misread this;
If the lights have an earth terminal they must be earthed, the CPC/earth must run continuously across all earth terminal points in fittings (junction boxes, lights, switches etc...) back to the distribution board, this then must be confirmed via testing and a Zs reading should be taken which complies to your set up.

 

[chris765]

Okay I somehow misread this

Yes I did too, I think

and earth (no

subconsciously read as no earth.

What's the earthing arrangement?

 

[EFLImpudence]

Can I assume that the earthing can be carried right back to the dis board rather than needing to earth each and every light?

I didn't understand the question.

 

[PrenticeBoyofDerry]

Can I assume that the earthing can be carried right back to the dis board rather than needing to earth each and every light?

I didn't understand the question.

I have the feeling that this mean't, the OP had continuity to all junction boxes, but had excluded the connection to light fittings via junction boxes.

 

[JohnW2]

Can I assume that the earthing can be carried right back to the dis board rather than needing to earth each and every light?

I didn't understand the question.

I have the feeling that this mean't, the OP had continuity to all junction boxes, but had excluded the connection to light fittings via junction boxes.

It clearly needs clarification. FWIW, given that the next sentence was:

What I could do if necessary is earth at the first junction box onto the brick work of the house, but not sure if this is necessary?

... my first impression was that he was perhaps trying to ask was whether the lights needed something like an earth rod - which is, of course, what a few (probably a very small number of) people might suggest (without connection of the installation's earth to the lights) if they were worried about exporting a TN-C-S earth toexposed metal in a flower bed!

However, we need to understand the question before anyone can really give an answer.

Kind Regards, John

 

[macadonald]

Hi all,

Sorry if I was not very clear, go tinto the office after a train trip to work and thought I'd quickly post the question.

JohnW2 is correct in that I was wondering whether the lights needed something like an earth rod. I do have continuity of the earth from each light, through the junction boxes and back to the dis board.

I donot think they arte classII double insulated, but will check tonight. My main concern was danger that should the metal post become electrified and each light is not earthed individually, would the earth back to dis board still be effective.

From what has been posted, I gather theis should be okay.

Ta

Maca

 

[EFLImpudence]

My main concern was danger that should the metal post become electrified and each light is not earthed individually, would the earth back to dis board still be effective.

That is the purpose of earthing and the circuit should be tested to determine that that will be the case.

 

[bernardgreen]

The earth connections have to be made in a way that ensures the continuity remains intact no matter what the weather throws at the joints.

If relying on the steel armour of the cable then piranaha nuts should be used where the cable is glanded into the junction boxes. Regular inspection for damage / corrosion at these joints would be a good idea.

Using a third core for the CPC ( earth ) is better, ( both can be used ).

The supply must be via an RCD.

Even with the earth via the cable I would put an earth rod at the far end as belt and braces. ( An extra earth in this situation has more pros than cons )

 

[plugwash]

There are pros and cons to both approaches.

Using the house earth will likely mean a low impedance earth and will therefore aid in the quick and reliable disconnection of faults in the lamp but if the house earth is TN-C-S then it's possible (unlikely but possible) that in the event of a fault in the electricity supply network it could rise up relative to real earth leaving everything connected to the houses earthing system live compared to real earth.

Using a local earth rod that is isolated from the house earth avoids the problem of network faults making the "earth" live but it will mean a much higher impedance earth. That means that in the event of a fault to earth in the lamp the casing of the lamp will briefly become live. It also means you will be reliant on RCDs to disconnect that fault.

 

[macadonald]

Thanks All,

Sounds like the consensus is to keep the continued earth back to the RCD/DIS board, but have an extra earthing rod on the very last light. This is easy for me to do and I'd rather be safe than sorry.

Out of interest, rather than running an extended earth wire to a rod in the ground, does it defeat the object if I simply earth it to the metal frame internally, which sits on a hardwood base, bolted onto a post knocked about a metre into the ground?

 

[JohnW2]

.... does it defeat the object if I simply earth it to the metal frame internally, which sits on a hardwood base, bolted onto a post knocked about a metre into the ground?

The metal frame of what?

Kind Regards, John