Online assistance for electrical trade people Login  |  Register  |   Forgot Password
Assistance for electrical trade people




Click here to send Ron a pdf document for publication on this Topic

Documents must be less than 200k in pdf format

Posted By Topic: Earthing for double insulated LEDs

Feb 06 2018 23:07

Hi guys, obviously the quick answer is 'they don't need an earth', but in the regs it says any additional lighting points require an earth. I usually only do commercial so this one I need help with. I am doing a job where all lighting is wired in 2 core. I have also upgraded & relocated the SB, so all RCD, and with the additional cable run I now have an earth from the new board, but only as far as a Jbox, as it's all existing switches fed with the 2 cores. Short of re-wiring the whole house, what is the best way to comply? I have also replaced some single batten lamp holders in some rooms (but not all) with double insulated LEDs, which the customer provided (from Bunnings, so SDOCs won't be an issue) which don't have an earth terminal and I had to cut the earths off, which I don't like doing but the cable entry could barely fit 2 tps, as I wanted to clamp down on the sheathing not the insulation, let alone feeding the earths back out to put them in a strippy. There is enough cable for any sparkie in the future to strip them back and have an earth if he needs one though. So my question is, if I run an earth to the first light in each room that has additions, is that compliant? Obviously there won't be continuity between fittings, but currently they don't need it anyway. Also as the switches are all existing (and plastic), and the existing lights don't have and earth anyway, can this be left as-is? I guess the rule changes will address this but I'm going to finish this job one day this week, so I'm hoping someone can help me out!

Feb 06 2018 23:40

Any new points need earths. Even if the fitting doesn't require one, and you must continue the earth to the next fitting - even if that doesn't require one either.

The earth conductor doesn't need to be double insulated, so it can be connected outside the terminal enclosure. But you did the right thing to keep the TPS sheath inside the terminal.

Any old lights wired in twin can remain as they are so you don't have to add an earth if you don't need it. But if you have access and want to do it, you can run a separate earth wire to the light point instead of rewiring. It doesn't need to go to the switch. That extra earth can be a green/yellow conduit wire. It must be minimum 2.5mm2. It can come from the earth bar at the switchboard, or it can connect to the main earth conductor (but that's a whole other story). If it's not required at the light fittings, I would loop it through and tape it onto the twin at each light point (keeping it continuous), so it's available in the future.

At the end of the day, when installing to existing wiring, it's the responsibility of the worker installing a fitting that requires earthing, to ensure it is earthed. But installing any new wiring, you need to provide the earth at each point, even if the fitting doesn't require it.

I've attached a photo of how I link through a LED driver. If there is two separate wires, I just use a connector outside the terminal space.


Feb 07 2018 09:03

DougP has pretty much covered it.

With fittings that lack space for looping cables, here's always the option of using a j-box, with a short length of flex/ TPS to the light. And some luminaires come with a plug, so you can just fit off a surface socket & plug them in.

There's no change coming on the requirement to have a PEC at each new lighting point.

Feb 07 2018 21:54

I’m sure most sparkles in NZ come across this situation: the homeowner wants new LED downlights throughout the house in place of the old batten holders which are wired in 1 mm2 2 c TPS. It’ll be interesting what others say about what they do (or what they don’t do) regarding earthing.

Feb 08 2018 07:35

The practice of one ot two electricians that I have come across is the running of the right number of cable cores (controlled phase, neutral and earth) to each luminaire position and then ommitting of connecting of the earthing conductor at every luuminaire position because double insulated ELV transformers are being used.

This position is not helped by the lack of an earthing looping point on each ELV transformer.

I have tried to get an earthing point to each ELV transformer without sucess into the AS/NZS standard. Interesting, the IEC standard makes provision for an earth looping terminal. So will keep on trying to get this looping terminal feature added to AS/NZS standard.

Feb 08 2018 16:18

Thanks guys for the replies, especially Doug with a clear explanation of how to interpret that clause. It looks like i'm going to have to re-terminate each downlight (all 24 of them-eek) tbh the hardest thing will be explaining the extra work to the customer I reckon! The inspector has been and signed off the new board and earth electrode I installed (old earth was just tapped of a waterpipe and into the house is all plastic now) And all the lights have been fitted. As far as he is concerned i'm only coming back to tie up some loose ends so hopefully he doesn't give me too much of a hard time...Anyway as all three lighting circuits have an earth from the board to a J box in the roof space, can I just run another TPS from those to the first light in each room, only using the earth conductor, and then from there loop in between the lights, or would it have to be a 2.5mm conduit from the earth bar in the board? The reason I ask is the wall the board is on is now closed up and painted, and the cable entries are now all fire-sealed so I would rather avoid all that if possible?

Feb 08 2018 16:48

just run from you j-boxes to the lights of each circuit.
I'd just use conduit wire for that as well; and leave an un-cut loop at each lighting point.

In fact using conduit wire you really only needed one conduit wire for all three circuits [ Exception to]; but better to keep them separate.

Feb 08 2018 17:35

Just to be clear, the exception to would only apply to a common PEC coming from the main earth bar, or a common PEC connected to the MEC. As shown in Fig 5.3
It can't come from the earth conductor of a different circuit.

If you use that common PEC coming from one of those two places, it can be used for all the circuits.

Feb 08 2018 19:19

Awhile back got called to 10 hallway step lights not working. Found the switch not working. Replaced, relivened. MCB tripped but RCD stayed on.(Owners then told me "oh, yeah, that happens every time we turned the switch on!!) Traced fault to rodent damage halfway along the cct. RCD wasn't tripping because someone had left every earth open at every electronic transformer. Rodent damage had burnt along about 30 cm of cable in the wall. House had only been built maybe 5 years prior.


Feb 08 2018 22:09

OK thanks guys, it seems like I'll be running a 2.5mm conduit wire from the board to the first light in each room, and then stripping back and re-terminating the TPS at the drivers putting the earths in connectors so there is continuity of earth to each point. I'll be able to record a true Zs value at the last point on each circuit too so I'll feel happy I've done everything right! Thanks again!

Feb 08 2018 23:07

Boatie, it's difficult to know exactly how you ran the wires and where you are missing the earth connections.

But you said "Anyway as all three lighting circuits have an earth from the board to a J box in the roof space," - So if you have an earth for each of the three circuits, just extend those to where your new twin&E cables are for each circuit, then connect all the missing joints.

I think that's probably what you meant in your previous post, but you said "just run another TPS from those to the first light in each room, only using the earth conductor", which is somewhat strange when you don't need the A & N for any reason. Whether you do it that way, or use a 2.5mm green/yellow conduit wire, it probably doesn't make much difference as far as the "rules" go.

Feb 11 2018 13:43

Sorry Doug, I obviously didn't explain it properly...The 3 original lighting circuits were wired completely in 2core, but because I didn't just upgrade the SB, but relocated it to another room, I had to extend those original 2 cores with modern TPS. That's why there is an earth as far as the Jboxes but no further. As those lighting feeds have been wired to the switches rather than top fed, I wouldn't be able to have a continuous earth to the lights from the Jboxes without rewiring all the feeds and the control cables, so basically the full rewire that isn't necessary as we've established above. I just wanted to know if I could tap off the Jboxes containing those switch feeds and take it over to the lights with a bit of TPS,only using the earth conductor, as it seems if I'm using conduit wire it needs to come direct from the earth bar, and access to the SB is now limited? Hope I'm explaining it a bit better!

Feb 11 2018 14:50

Just run in 2.5 G/Y conduit wire from your J-box to any lights (or at least any new ones) that are fed from that circuit.

The conduit wire option doesn't have to be conduit wire all the way from swbd; that's just the usual way of coping with existing circuits wired in twin. You've gone a step further and replaced the first par of each circuit with T&E; but that doesn't mean you need to run T&E to get a PEC to the lighting points.


Feb 11 2018 16:24

Thanks AlecK, I just wasn't sure if I could run a conduit wire unless it was straight from the SB. Also upon re-reading I now see that I would only need to run the 2.5 G/Y straight from the board if it was shared between circuits, as I already have an earth conductor available for each local lighting circuit I'll just tap off the Jboxes. Thanks for clarifying!