Did it really need an earth?

[rickyrt]

I was away at the weekend & the electrician came round to fix something. While there he decided to condemn an outdoor electrical light as he said it didn't have an earth. My wife didn't know better so she agreed to pay him.

It is a lamp post 8ft tall made entirely of aluminium with a single bayonet light fitting inside then a glass housing. It has been there since the 1980's without any problems. The lamp post is connectd directly into the soil - no concrete or anything like that.

It was originally wired up with just 2 wires live & neutral, then the cable went underground a few metres before being plugged into an outlet in the garage with a 3 amp fuse on the plug.

The electrician ripped out the cables and replaced with an earth, live and neutral. I assume he connected the earth to the aluminium case as no other place to connect on a light socket.

Every scenario I run through this is a complete waste of time as the lamp post is earth directly to the ground already and has been for 40 years. It is basically just a metal tube & a boyonet light socket on top.

Any earthing fault could only be live contacting the case and causing the housing to be live unless the breakers go off.

Any short circuit could only be the live & neutral wires touching somewhere - the fuse would likely blow anyway. Any fault in the cable underground would just earth to ground until sufficient to blow the breakers.

He connected the new wiring to an existing switch which was running off a 6amp breaker - which I now consider less safe than the 3amp fuse in the plug.

The lamp post is 20 metres from the house, so his new earth connection has to go 20m to the garage into a junction box, from there another 20m to the house where it hits another junction box, then 15m of earth cable before it connects to a steel steak hammered into the ground.

My understanding of electrics is electricity will flow down the path of least resistance so most likely from the case directly into the earth. It will not flow down the newly installed earth wire. The case is aluminium quite a good conductor.

So I see this as a complete waste of time - I appreciate there are probably rules that everything must have an earth in the UK - but this is my own home & it has been there for 40 years without problem.

Could anyone share there opinions please - is this electrectrician an idiot - am I the idiot? Or did the electrician just cheat us for money?

Is the electrician really following the rules - do we not allow even the slightest amount of common sense to be applied in the modern world?

 

[westward10]

We need a lot more info. Some of these columns are Class II and if installed correctly would not need an earth. Some pics of the lamp holder and other connections would be useful.

 

[Risteard]

Just to add though, assuming it's Class I then being imbedded in the ground does not remove the need for a circuit protective conductor and the protective devices may not operate with an Earth fault leaving the chassis live. So on the face of it it sounds completely reasonable and necessary what was done.

 

[brianmoooore]

He connected the new wiring to an existing switch which was running off a 6amp breaker - which I now consider less safe than the 3amp fuse in the plug.

A 3A fuse does not blow at 3A and a 6A breaker doesn't disconnect at 6A. These are the maximum continuous running currents.
The times they take to disconnect the load depends on how much over the maximum currents the fault current is, and is shown in graphs in the wiring regs.
In most cases that are likely to occur, the 6A breaker will disconnect in a shorter time than the 3A fuse.

 

[timhoward]

Any fault in the cable underground would just earth to ground until sufficient to blow the breakers.

This is unlikely as the impedance would be too high to trip a breaker or blow a fuse. Not enough fault current would flow. It might however trip an RCD.

Any earthing fault could only be live contacting the case and causing the housing to be live unless the breakers go off.

This was enough to kill a kid in a pub car park btw and isn't a scenario to brush aside too quickly. Again, over-current devices wouldn't operate in your case due to the nature of your house earthing arrangements. You'd be relying on the up-front RCD or RCD main switch to save you.

I think if you measured the impedance of your earth electrode (stake) and the impedance of the lighting column there would be a better result for the earth electrode, and so earthing it properly would reduce the touch voltage further under fault conditions.

But even leaving the nature of the column aside, I'm struggling to think of scenarios where the regs allow you to take fixed wiring underground without a cpc (earth).
I note it was originally on a plug top - did it originally come with a plug on it or was that put on when it was installed?

 

[telectrix]

also, even if the lamp itself is class II, the cable to it needs to incorporate a cpc,

 

[Lucien Nunes]

My understanding of electrics is electricity will flow down the path of least resistance so most likely from the case directly into the earth. It will not flow down the newly installed earth wire. The case is aluminium quite a good conductor.

It will flow along all available parallel paths, in inverse proportion to their resistances. The resistance of the earth cables (a few ohms at most) is likely to be much lower than the resistance of either the lighting column or the earth rod into the mass of earth (maybe 50-500 ohms). Therefore what matters is the relative quality of contact with the mass of earth; if the rod is better, then more of the current will flow to the rod despite the distance.

If the rod goes deeper than the column, which it probably does, then in dry weather it will offer a better earth as it will be less affected by seasonal soil conductivity variations. The fact that the column is aluminium is also important, because although aluminium is a good conductor, its surface exposed to air and water forms a coating of oxide that is a good insulator. Therefore it cannot be relied upon as an earth electrode because contact with the soil will only occur where the oxide layer is penetrated and has not re-formed. (This is one of the reasons aluminium is not used for domestic wiring, as it requires special techniques to make a connection to it that reliably overcomes this insulating surface layer.)

Therefore aside from the regulations, physics suggests that the rod will offer a more reliable earth than the column's own contact with the ground, even if its lowest resistance isn't actually that much lower.

 

[timhoward]

Is the electrician really following the rules - do we not allow even the slightest amount of common sense to be applied in the modern world?

I'd say unless you can prove the lighting column is class II and originally came with a flex and moulded plug, the electrician has it right. At least 3 requirements in the regs are coming to mind (don't have book, this is the gist)
Section 4:
Exposed conductive parts shall be connected to a protective conductor
A protective conductor shall be connected to every point in the wiring system and every accessory (whether ultimately connected at the end or not) unless it's a ceiling rose bayonet fitting.
Section 5
Cables buried underground (unless in ducting) shall incorporate an earthed metallic armour, sheath or both, capable of acting as a protective conductor.

It is in fact common sense to connect a lump of metal in your garden that has a live wire running up the middle of it to earth.

Yes, I certainly do bend rules sometimes and apply common sense, I could write a book of regs I've broken and why, but not in the area of fault protection that can land me in the clink if I skip things and someone dies.

 

[littlespark]

On the other hand... this electrician has spotted something many others may have missed if they were there doing another job entirely. He may have possibly saved a life here... re, the pub mentioned in #5 where many opportunities to spot a fault had been missed.

A better idea would have been for him to remove the lamp post from power, cut the plug off and give you a quote for putting it right.
If you had then plugged it back in again, then that's on you.

 

[marcuswareham]

also, even if the lamp itself is class II, the cable to it needs to incorporate a cpc,

Very good point

Although if it was installed to a previous edition of bs7671 and met the previous standard and was not being altered etc then could you argue nothing needed to be changed

 

[brianmoooore]

If this was installed in the '80s, it did not meet the regs at the time of installation.
I would notify the customer in writing that I consider the installation to be dangerous even if it was installed much earlier, and did meet the regs at that time.

 

[westward10]

Without further info we have no idea if an earth was required.

 

[brianmoooore]

Without further info we have no idea if an earth was required.

OP says it dates from the '80s.

 

[westward10]

OP says it dates from the '80s.

Very true but more info will confirm things.