Downlights - to Earth or not to Earth?

[braychurchmouse]

Ok, I know some of you are not fond of downlights, but the OH has spoken. So I picked up a couple from TLC - GUFRD50 with halogen bulbs). http://www.tlc-direct.co.uk/Technical/DataSheets/JCC/GUFRD50.pdf

Its a cloakroom so not too worried about efficiency, but maybe someday I'll replace with LED).

I'm deciding on wiring (they'll come off an Autenco proximity detector) and noticed that they have a L,N and E connecting block, with the Earth on the connecting block not actually connected to the casing, or anything else. The instructions say "This fitting is Class II with provision for Earth termination". So presumably if I wanted an Earth I would connect the terminal block to the casing with a short wire (there's a screw that looks as though its intended for this.)... and then the earth in the cable into the terminal block obviously.

So just wondered whether to link in to an Earth connection or not? What is normal way of doing this? and is there anything in regs that proscribes this.

The Autenco PIR doesn't have any Earth connection so I'd bypass that.

I'm conscious of the tripping problem that someone had in this thread with a unconnected Earth //www.diynot.com/forums/viewtopic.php?t=235012&start=15, although as its a cloakroom I don't anticipate any moisture problems.

Thanks in advance for any advice.

 

[Taylortwocities]

The earth, from teh supply end (probably your PIR) needs to be carried though the cabling to the final downlight.

This is connected using the bare conductor in the 3 core cable. (That's why its called two core and earth).

The earth connection does not actually earth each downlight as they are Class II. So it can probably loop through that "earth provision" terminal.

 

[EFLImpudence]

"This fitting is Class II with provision for Earth termination". So presumably if I wanted an Earth I would connect the terminal block to the casing with a short wire (there's a screw that looks as though its intended for this.)... and then the earth in the cable into the terminal block obviously.

No. It's just somewhere to connect a CPC (earth) which is not required.

So just wondered whether to link in to an Earth connection or not?

No. Class II items must not be earthed.

I'm conscious of the tripping problem that someone had in this thread with a unconnected Earth

That was because of a fault - not because it was not connected.

 

[braychurchmouse]

thanks folks, thats very clear. I'll just terminate the CPC in the connector block, using it for loop through on the intermediate lights.

I'm still puzzled how a fitting with metal casing can be safe without a connection to CPC...I thought that was why we had CPC!

Would it actually be dangerous to connect the casing to the CPC? There seems to be a lot of conflicting advice on this. Some saying definitely NOT.

 

[EFLImpudence]

I'm still puzzled how a fitting with metal casing can be safe without a connection to CPC...I thought that was why we had CPC!

The CPC is to operate the protective device should the live conductor contact the metal.
The double insulation prevents this so it is not necessary.
Preventing it becoming live is better than something switching off when it does.

A fault elsewhere and the protective device not operating could make the CPC live.
It's a compromise of the most/least likely occurrence(s).

Would it actually be dangerous to connect the casing to the CPC? There seems to be a lot of conflicting advice on this. Some saying definitely NOT.

It COULD be and it will be no safer if the casing were earthed.

 

[braychurchmouse]

Sorry to come back on this, but am wondering why I should even use 1.5 or 1.0 mm T&E if the earth/cpc is not used. The supply will come off a double pole isolating switch to the Autenco PIR. which has no earth connector, just three connection points Live and neutral in and switched live out with the neutral looped out. So could I just have twin going from isolating switch to Autenco, and again just twin to the downlight. As the house was built 1976 the lighting circuits are 1.0mm with 5 Amp MCBs.

Could I use 2 core 1mm 10 Amp PVC flex (clipped of course) eg TLC 3182Y CA 1F2 http://www.tlc-direct.co.uk/Products/CA1F2slash50.html or maybe 1.5mm just in case anybody rewires the rest of the house. Or does lighting cabling now always have to be 1.5mm even if the MCB is 5 amps and the rest of the cabling 1.0mm.

Seems pointless stringing an unused CPC cable all the way from the switch box to an unconnected terminal strip on the downlight.

 

[EFLImpudence]

Could I use 2 core 1mm 10 Amp PVC flex (clipped of course)

No. Use three core 1mm² flex.
The instructions state you should use heat-proof or silicone.

Or does lighting cabling now always have to be 1.5mm even if the MCB is 5 amps and the rest of the cabling 1.0mm.

No, funny how these things start. 1mm² can carry 16A (not under thermal insulation - even there 8A).

Seems pointless stringing an unused CPC cable all the way from the switch box to an unconnected terminal strip on the downlight.

No, it's essential.

1mm² is the minimum allowed for 'lighting circuits' but 0.75mm² can be used for specific items - manufacturer's instructions allowing.
So it depends how you wire them.

 

[ban-all-sheds]

Its a cloakroom

As in somewhere you hang cloaks?

Or a WC?

If the latter then using a detector instead of a switch will drive you mad - don't do it.

 

[pjcomp]

... am wondering why I should even use 1.5 or 1.0 mm T&E if the earth/cpc is not used.... Could I use 2 core

Theoretically yes you could. In the future the light fittings might be changed to one that needs the CPC, then you'd have to recable, so leave the CPC in place for future-proofing.

PJ

 

[RF Lighting]

Not forgetting that the regs require a CPC to be run to, and terminated at every point and accessory within the fixed wiring installation.

 

[braychurchmouse]

Thanks all for the advice and guidance.

I guess if the regs say so, then so be it, I'll put in a redundant CPC with heatproof 3 core 1mm flex.

Ban...Its a WC, but I've thought about it. I'll put a long delay on and its light sensitive/adjustable. There's a separate Autenco for the fan so that can be adjusted to ignore the light level. There is also double wall switch cabled in initially as an "over-ride off" so if it doesn't work properly I'll revert to having simple on/off switches.

I'll let you know how I get on, though progress is slow!!!