Replacing 12v transformers with LED drivers

[maccas17]

I'm replacing the 20W GU5 halogens in our kitchen with LED bulbs. I have suitable bulbs and also got LED drivers to replace the transformers, as I noted some of the existing ones had minimum load ratings and wouldn't be suitable.

I checked the existing setup and the mains twin & earth cable goes into a 20A junction box; the earth is unsheathed and cut short and not connected. The live an neutral cables are both connected to the same from the transformer in the junction box. The plan was a simple straight swap over so I ensured the 12v 20W LED driver I purchased online had just live and neutral connections for the input cable, which was clearly pictured. However, what has been delivered actually has live, neutral, and earth connections.

I simply just wanted to swap out the old transformer with the LED driver with the exact same connections. I've complained to the company I purchased from about their inaccurate product pictures; they've apologised, but state all their 20W drivers have an earth connection. The most the bulbs should draw is just under 11W, but I wanted some headroom in case I have LED strip lights added in the future.

What is the correct approach to handle the earth connection in these circumstances? If this requires a specific type of junction box could you please suggest some products?

If it's not going to be within my capability to replace these transformers, then my options are to either try and send all the LEDs and transformers back (which I don't really want to do) or find a local electrician. Any ballpark figures on how much an electrician might cost to sort this?

 

[rogerdygas]

Can you cut a bit more of the outer insulator back to reveal more earth and then put a bit of sleeving on the earth and connect as normal? If your junction box doesnt have three terminals you can buy a new one from just about anywhere. You should also check the origin of the cable and make sure the earth is connected.

Alternatively you could look for another driver that doesnt require the earth (if such a thing exists)

 

[333rocky333]

Is the earth terminal in the drivers connected to anything, not sure about drivers but some transformers have an earth terminal provided to park an unused earth or to loop through, sometimes the terminals just fixed to the plastic case and not actually earthing anything within the unit
Is there a double insulated symbol on the drivers.

 

[ban-all-sheds]

You should also check the origin of the cable and make sure the earth is connected.

Don't trust your life to the handiwork of the sort of person who would cut earth conductors back.

 

[Iggifer]

i suspect the earth terminal in the transformer doesn't actually earth anything, as rocky says, it's likely there just to park the earth. Check for the double insulated logo.

As the output from the transformer is only 12VDC, you won't be earthing the secondary side anyway.

I would still want to cut the supply cables back and get the earth into a terminal in the JB & sleeve it though, it's just better like that

 

[maccas17]

Thanks for the responses.

The LED driver is not double-insulated (there is no class II symbol or marking I can see) and it does feel like a metal, not plastic case - this is a picture of it:

View media item 60002
Below is a picture of the junction box I have with the unsheathed earth connection visible (the halogen transformer has been disconnected at this point):

View media item 60003
So an acceptable approach is to strip back the mains cable to expose the earth, sheath this and connect into a terminal in the JB with the earth from the LED driver?

I think in the end I'm going to have to get someone in to review and check all the wiring in the house (not moved in long ago) so we can be sure there are no issues. Just need to save some pennies - any rough ideas how much it would cost to get an electrician in to do this? Is it an hour or two's work or more like a day?

 

[ericmark]

One can still buy toroidal transformers which will work from zero to rated output. These are in the main SELV outputs and do not require an earth. I still use the larger version

to power my LED lamps originally were tungsten. I now have 4 x 0.58W lamps running off a 100VA transformer.

Philips it would seem have made some LED lamps designed to run from the inverters not sure how they work but they say can be used as direct replacement without changing the inverter.

As already said likely the earth connection is only to give some where for the wire to be terminated and is not connected, however I would have thought the supplier would have told you that so may be it is required?

For an electrician job is easy, he puts the loop impedance tester on the earth wire and he knows if connected or not. However although DIY people should use the same inspection and testing as an electrician we all know you don't. Good reason is the meters cost so much.

Although there are other ways to test the earth to try to explain on a forum is not really the way I would want to go. I would never cut the earth, tape it back and not use yes but would never cut it off. So one has to ask has he connected it the other end?

So you really have three options.
1) Get an electrician to do the work.
2) Swap the driver for a device which does not require an earth.
3) Find the markings which show the device does not need an earth.

There are two markings the double square showing double insulated and the shield with two overlapping circles showing it to be an isolating transformer.

or

 

[ericmark]

Just seem photos it would seem you can't use that power supply with what you have.

 

[maccas17]

3) Find the markings which show the device does not need an earth.

There are two markings the double square showing double insulated and the shield with two overlapping circles showing it to be an isolating transformer.

or

I already checked for the double square and it's not on the LED driver; neither is the shield version. There is nothing on the underneath, so all the markings are visible in the picture I posted.

 

[maccas17]

Just seem photos it would seem you can't use that power supply with what you have.

Ok, any more details as to why you state this?
Thanks.

 

[ericmark]

I will guess and clearly only a guess that should the unit be short circuited for example the case may become live or it would likely have one of the logos I have shown. Therefore it must be earthed. Where earths have not been connected to reconnect also means you need to test to see if disconnected else where. For an electrician no real problem we have a loop impedance tester which puts a load on the earth for a very short time and tells us if it's OK. There are other meters able to test the earth while the circuit is dead. The low ohm meter will do this but to ensure no errors the regulations say it must use at least 200ma with the test which rules out most multi-meters they just do not use enough current to ensure a good connection. Both meters are not cheap and likely it would be cheaper to get an electrician to do the work than hire the meters required even if you know how to use them.

So to use the power supply you have in real terms it means getting an electrician to do the work.

Buying transformers which don't require an earth is the other method. Or buying lamps which will work with the existing inverters is the third way forward. I would not want to use the special Philips lamps as it would be all too easy in the future to forget you used special Philips lamps and replace them with cheaper versions which don't trick the inverter into thinking it has a larger load.

There are socket testers with a simple loop test cost around £50 and in theory you could temporary fit a 13A socket and plug in the tester to see if the earth is OK. But at £50 is it really worth all the hassle?

I clicked on the link I gave and at £11:30 plus vat for a 50W transformer is it really worth all the hassle? It says "Conform with IEC 742 for class 11 installation of SELV lighting." so I would assume it does not require an earth but I would ring and ask to be sure. The larger version

one can see the signs on the side of the unit showing it as being Class II. OK at £44 ex-vat getting expensive but still cheaper than buying a tester. the tester shown will test for earth at £46.74 not cheap and you still need to mess around with fitting a socket on the supply before you can plug it in.

 

[EFLImpudence]

What am I missing?

Why not just use 240V fittings?

Class II if the earth is not there.

 

[maccas17]

What am I missing?

Why not just use 240V fittings?

Class II if the earth is not there.

Because I'm replacing 12V Halogens with 12V LED bulbs, that I've already bought. Like for like swap was my original plan.

 

[ban-all-sheds]

I already checked for the double square and it's not on the LED driver; neither is the shield version. There is nothing on the underneath, so all the markings are visible in the picture I posted.

It was pointless to ever look.

It has a 3-core supply cable - it needs an earth connection.

 

[maccas17]

Both meters are not cheap and likely it would be cheaper to get an electrician to do the work than hire the meters required even if you know how to use them.

I would only be interested in basic fault diagnosis really, so I could be sure there was an issue and then get an electrician out to investigate and resolve. The plug-in tester unit you showed looks quality, but probably too much expenditure for the occasional DIY user like myself. Putting the hassle of fitting a socket for this specific case to one side for now - would you think there is any value in getting the following for testing sockets etc. or do you need to spend ~£50 to get something that is reliable?
http://www.screwfix.com/p/ced-plug-in-socket-tester/76975

Buying transformers which don't require an earth is the other method.
I clicked on the link I gave and at £11:30 plus vat for a 50W transformer is it really worth all the hassle? It says "Conform with IEC 742 for class 11 installation of SELV lighting." so I would assume it does not require an earth but I would ring and ask to be sure.

In hindsight I would have bought something like what you recommend for sure, especially as the ones I got were a bit more than £11.30 - though originally this is what I thought I was getting, below is the picture from the website I purchased from (clearly showing both input and output cables only contain 2 connections):

View media item 60008
As to the larger models you mention, £44 a pop is too much for this job, though being double insulated and with two outputs it's clearly better than what I've got. Interesting to see the next level up options.

So just for my understanding as I need to decide whether I try and send everything back tomorrow - if the mains earth connection was confirmed as ok this LED driver could be used as long as its earth connection and the one from the mains were connected inside the JB?