# Do i need to earth a BC Cap Lamp



## sr20det (24 May 2012)

I have a BC 30w Daylight Bulb, and plan was to use this for my nano aquarium light. Now the lamp batten I had found was a 2 point socket and I have an old 2 core main plag wired and bingo, it works. But then wondered, about the earth, in most cases I have seen 3 core wire used, now days in homes, and one being the earh, but the socket doesnt have a slot for it, so wondered if I need a new lamp batten.  With 3 core?

Dont know much about electrical, and seeing its around my tank dont want to electricute my self either?


Hoping someone knows about wiring and electrics?

Am I being paranoid?


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## ian_m (24 May 2012)

Earthing is not meant to protect you, a very common misundertanding.

Earthing is meant to provide a suitably low resistance path to "earth" in case the live conductor touches any metal that the user could touch, think of say washing machine, fridge etc. In such a case, if live did accidentaly connect to the metal, due to the suitably low resistance to earth, the fuse would blow or breaker trip rather than expose the user to a metal case connected to live.

Thus earthing anywhere in the lamp eg fitting would probably not protect you if you say dropped the light in the water. It would only protect you if the live got accidentally connected to the earthed metal, which considering the way these things during "normal use" you could not touch and metalwork near the wires.

However I would suggest an RCD (residual current device). These measure the difference between the live current and return neutral current (residual bit) and if they differ by more than 30mA cuts the power. These would probably cut the power if the lamp fixture was dropped in the water and if not, would certainly trip if you touched the "live" water.

Your house (if modernish) may already have RCD's on the mains if not you can buy plug in ones quite cheaply.

Try not to put everything on one RCD as if something misbehaves (ie light) then you loose power to all your devices.

In all the years of fish keeping, I have, touch wood, never tripped the house 30mA RCD, despite water getting into electrical places it shouldn't do, wet extension leads, dropping light fixture whilst in in the tank etc etc.


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## sr20det (24 May 2012)

ian_m said:
			
		

> Earthing is not meant to protect you, a very common misundertanding.
> 
> Earthing is meant to provide a suitably low resistance path to "earth" in case the live conductor touches any metal that the user could touch, think of say washing machine, fridge etc. In such a case, if live did accidentaly connect to the metal, due to the suitably low resistance to earth, the fuse would blow or breaker trip rather than expose the user to a metal case connected to live.
> 
> ...




Thanks for that mate, well i was planning on mounting the light unit to a metal tin to act as a reflector.

i.e i have one of these:

http://www.diy.com/nav/fix/electrical/s ... nt=Default

And 2 core wire going to a 3AMP (i think) mains socket, and all seems ok.  But because the back where the wire exits onto the metal tin though I would earth or something.

I think the house does have a RCD in the junction box already.


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## ian_m (24 May 2012)

sr20det said:
			
		

> ...Thanks for that mate, well i was planning on mounting the light unit to a metal tin to act as a reflector.


Then I would earth the metal tin, as touching the metal is something that would occur during "normal use".  It definately says in the wiring regulations (I only have 16th edition at work, 17th is current) that this type of thing should be earthed as you can touch during normal use and you are not allowed to depend on the RCD alone.


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## sr20det (24 May 2012)

ian_m said:
			
		

> sr20det said:
> 
> 
> 
> ...



Thanks mate, Thats the thing, I always assume I would earth to the mains plug, do I just earth tin to braket holding it which is  also metal? It sits on a wooden table? Next to the wall?  It would all be steel, as the tin will be hanging by metal chain from a metal bracket above? bracket clamped to the wooden table.


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## ian_m (24 May 2012)

You need to earth where any "wire failue" (broken insulation, wire pulled out of connector etc) would allow metal to become live and the user can touch the metal. End of light fixture sounds a prime candidate.

So as you are having to run a wire down the chain for the light anyway I would earth the tin on the end of the chain.

As for the attaching bracket & clamp, probably not needed to earth as I suspect your cable won't be near them and therefore no possibilty of connecting to live.

I have a light in my lounge on a chain and that is earthed on the hanging end (via the connecting cable) and metal ceiling rose via short jumper wire. Note that a lot of old houses do not have earth connection in ceiling roses and due to the serious number of electrocution incidents involving light fixtures 17th edition of domestic wire now specifies RCD's on lighting circuits, which was never the previous case. My house built in 2000 does not have RCD's on lighting circuits, but at least it has earth connections....


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## sr20det (25 May 2012)

ian_m said:
			
		

> You need to earth where any "wire failue" (broken insulation, wire pulled out of connector etc) would allow metal to become live and the user can touch the metal. End of light fixture sounds a prime candidate.
> 
> So as you are having to run a wire down the chain for the light anyway I would earth the tin on the end of the chain.
> 
> ...



Thanks mate, will do just that   Back of the light does look the most likely risk.  I may add some duck tape to the back as an insulator but still, earthing is probably wise.


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## dw1305 (25 May 2012)

Hi all,
If you buy any German filters, household appliances etc, they are all "double insulated", with this 
symbol 


 and a 2 core cable.

This means they don't have an earth connection, but all conducting surfaces are insulated, so that you can't touch them.
Double insulation is inherently safer than earthing, but obviously this falls down when you DIY something that isn't double insulated using a 2 core cable, which is potentially very dangerous. 

Like Ian says it is best to always refer to the 16th Edition IEE Regulations (on the really useful TLC web site: <http://www.tlc-direct.co.uk/Book/5.1.1.htm>.

cheers Darrel


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## ian_m (25 May 2012)

I think this sums up what you are trying to prevent.


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## sr20det (25 May 2012)

See,I am no expert, safety is a must off course, maybe the tin idea was bad, and should got for plastic, or other instead. Hmmm.   Its why I asked, as I just was a little paranoid.


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## ian_m (25 May 2012)

Earthed metal reflector will be fine and safe.

I suspect plastic reflector and a conventional bulb will have heat & melting issues.

Why not use LED light ? They are low voltage so earthing metalwork might not be necessary ?


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## sr20det (25 May 2012)

ian_m said:
			
		

> Earthed metal reflector will be fine and safe.
> 
> I suspect plastic reflector and a conventional bulb will have heat & melting issues.
> 
> Why not use LED light ? They are low voltage so earthing metalwork might not be necessary ?



Price really, I would love LED, and thay are great in portability, but to get my 2watts pg, an LED would cost a lot, I think the 30w 6400k Daylight I have would be better and it only cost me £10.  I may justt ran an earth from tin to chain or steel braket that holds the chain   Its a nano by the way, well 25ltrs.

I purchased a 48 LED light for my other Nano (in the making, should do journal soon enough), but seeing I am only growing crypts, ferns and mosses in that tank, the light should suffice.


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