(Apologies if this has been covered before)

Is there reason to wire the earth core in a single room LV Lighting
loop where there is one transformer per lamp?

There is nothing to earth so the only reason I can think of is that in
the future some might want to replace the low voltage lights with
something else (which needs earthing) in the future. In which case
they probably want to rewire the whole room anyway.

The diagram below should hopefully clarify things.


240V -------------------------JB
| | | |
| | | |
Tr Tr Tr Tr ---- Transformers
| | | |
12V | | | |
Lamp Lamp Lamp Lamp


Thanks in advance

Charlie

"Charlie" wrote
| Is there reason to wire the earth core in a single room LV
| Lighting loop where there is one transformer per lamp?
| There is nothing to earth so the only reason I can think of
| is that in the future some might want to replace the low voltage
| lights with something else (which needs earthing) in the future.
| In which case they probably want to rewire the whole room anyway.

You *must* continue the earth core to the transformers on the mains side as
*all* circuit wiring must have a circuit protective conductor (earth wire).
You do not need to connect the earth in the low-voltage side; the
low-voltage cable may not be suitable for mains use anyway.

Owain

Charlie wrote:

Is there reason to wire the earth core in a single room LV Lighting
loop where there is one transformer per lamp?

Yeah - the Regs say it's no-fair to assume no-one will want to replace
existing fittings with ones that need an earth. (And many LV fittings
*do* need earthing, anyway).

And since you'll be wiring the lighting points with 1mmsq or 1.5mmsq T&E
anyway (you will, won't you - you weren't going to use that bit of
2-core flex you had lying around for permanent wiring, were you!?), the
'extra' work in running the E core of the T&E, sleeving it, and either
attaching it to the fitting's earth point or coiling it up neatly in its
sleeving to earn good karma from whoever makes the next change - which
may be yourself in 5 years' time - is scarcely going to blow your time
and effort budget...

Stefek

Stefek,

I've run 1.5mm cable so I have the earth there -
I was just very lazy/naughty when I first did it.
It's been bothering me since - didn't know if the 240V passing between
the junction boxes should be earthed properly.

I think I shall go back and strip the wire back an inch or so to give
me the earth and connect it up.

Charlie

Owain wrote:

"Charlie" wrote
| Is there reason to wire the earth core in a single room LV
| Lighting loop where there is one transformer per lamp?
| There is nothing to earth so the only reason I can think of
| is that in the future some might want to replace the low voltage
| lights with something else (which needs earthing) in the future.
| In which case they probably want to rewire the whole room anyway.

You *must* continue the earth core to the transformers on the mains side as
*all* circuit wiring must have a circuit protective conductor (earth wire).
You do not need to connect the earth in the low-voltage side; the
low-voltage cable may not be suitable for mains use anyway.


Sadly, most transformers have nothing to screw it to.

I usually leave it ina junction box in the ceiling at the end of the
mains T & E, and just connect the transformers two wires up...

Owain

The Natural Philosopher wrote:
Owain wrote:

You *must* continue the earth core to the transformers on the mains
side as
*all* circuit wiring must have a circuit protective conductor (earth
wire).
You do not need to connect the earth in the low-voltage side; the
low-voltage cable may not be suitable for mains use anyway.


Sadly, most transformers have nothing to screw it to.

I usually leave it ina junction box in the ceiling at the end of the
mains T & E, and just connect the transformers two wires up...

Why is that lighting kit which doesn't have any need for an earth (which
is a large proportion of it these days) never has a place to park the
redundant earth lead? I'll bet there are plenty of instances where
not-so-competent amateur electricians have just left the earth wire
flapping around uninsulated in the breeze, where it could easily come
into contact with somewhere it shouldn't.

Is there some reason? Maybe if there was a non-functional earth wire
'parking' terminal it could be construed as being legally functional or
something daft like that??

Charlie wrote:

(Apologies if this has been covered before)

Is there reason to wire the earth core in a single room LV Lighting
loop where there is one transformer per lamp?

There is nothing to earth so the only reason I can think of is that in
the future some might want to replace the low voltage lights with
something else (which needs earthing) in the future. In which case
they probably want to rewire the whole room anyway.

The diagram below should hopefully clarify things.


240V -------------------------JB
| | | |
| | | |
Tr Tr Tr Tr ---- Transformers
| | | |
12V | | | |
Lamp Lamp Lamp Lamp


Thanks in advance

Charlie

AFAIUI the purpose of the earth core in the mains side of he wiring
(assuming a double insulated transformer) is to protect the _wiring_ if,
for instance,a nail is driven through it. There is a path to earth so
the mcb (or whatever) will trip.

Malcolm

Lobster wrote:


Why is that lighting kit which doesn't have any need for an earth (which
is a large proportion of it these days) never has a place to park the
redundant earth lead? I'll bet there are plenty of instances where
not-so-competent amateur electricians have just left the earth wire
flapping around uninsulated in the breeze, where it could easily come
into contact with somewhere it shouldn't.

Not to mention not-so-competent 'pro' electricians, and even more so
general builders just doin' a spot o' wirin'...

Is there some reason? Maybe if there was a non-functional earth wire
'parking' terminal it could be construed as being legally functional or
something daft like that??

Shouldn't have thought it's anything like as sophisticated as that -
just puts a couple of pennies on the manufacturing cost, which is quite
enough to make the beancounters put you on a pyre of lever arch files!

On Thu, 20 Jan 2005 17:37:27 GMT, Malcolm Race
strung together this:

AFAIUI the purpose of the earth core in the mains side of he wiring
(assuming a double insulated transformer) is to protect the _wiring_ if,
for instance,a nail is driven through it. There is a path to earth so
the mcb (or whatever) will trip.

Amongst other things yes, it's not the only reason for it being there.
--

SJW
Please reply to group or use 'usenet' in email subject

"Stefek Zaba" wrote in message
news
Lobster wrote:


Why is that lighting kit which doesn't have any need for an earth (which
is a large proportion of it these days) never has a place to park the
redundant earth lead? I'll bet there are plenty of instances where
not-so-competent amateur electricians have just left the earth wire
flapping around uninsulated in the breeze, where it could easily come
into contact with somewhere it shouldn't.

Not to mention not-so-competent 'pro' electricians, and even more so
general builders just doin' a spot o' wirin'...

Is there some reason? Maybe if there was a non-functional earth wire
'parking' terminal it could be construed as being legally functional or
something daft like that??

Shouldn't have thought it's anything like as sophisticated as that -
just puts a couple of pennies on the manufacturing cost, which is quite
enough to make the beancounters put you on a pyre of lever arch files!


"Stefek Zaba" wrote in message
news
Lobster wrote:


Why is that lighting kit which doesn't have any need for an earth (which
is a large proportion of it these days) never has a place to park the
redundant earth lead? I'll bet there are plenty of instances where
not-so-competent amateur electricians have just left the earth wire
flapping around uninsulated in the breeze, where it could easily come
into contact with somewhere it shouldn't.

Not to mention not-so-competent 'pro' electricians, and even more so
general builders just doin' a spot o' wirin'...

Is there some reason? Maybe if there was a non-functional earth wire
'parking' terminal it could be construed as being legally functional or
something daft like that??

Shouldn't have thought it's anything like as sophisticated as that -
just puts a couple of pennies on the manufacturing cost, which is quite
enough to make the beancounters put you on a pyre of lever arch files!

So it is the same reason you never get light fittings with 4 decently sized
terminals to accommodate 1.5mm^2 cable for loop-in wiring. Damn those
pennies.

Adam

"Lobster" wrote in message
...
The Natural Philosopher wrote:
Owain wrote:

You *must* continue the earth core to the transformers on the mains
side as
*all* circuit wiring must have a circuit protective conductor (earth
wire).
You do not need to connect the earth in the low-voltage side; the
low-voltage cable may not be suitable for mains use anyway.


Sadly, most transformers have nothing to screw it to.

I usually leave it ina junction box in the ceiling at the end of the
mains T & E, and just connect the transformers two wires up...

Why is that lighting kit which doesn't have any need for an earth (which
is a large proportion of it these days) never has a place to park the
redundant earth lead?

Possibly because the kit is 'homogenised' to work Europe wide and over half
of them don't have an earth in the lighting wiring. Though I notice more
and more transformers are moving to using an external choccy block anyway so
you can always use a three pin one.