GU5.3 12v or 240v - how to identfy

[333rocky333]

At a quess, maybe there thinking is that the only imediate risk is from the connecter block shorting to there said bracket, and there asuming the holder and wire is not a potential risk, therefore the spring is just a convenient way of supporting the bracket.

I did once fit some lights that had copper shades, they suspended on 2 core cable, however they had made a point of using, plastic sleeves where the wires passed through the metal shade and used non conductive holders.
So maybe Luminaire makers have there own guidelines regarding this.

 

[JohnW2]

At a quess, maybe there thinking is that the only imediate risk is from the connecter block shorting to there said bracket, and there asuming the holder and wire is not a potential risk, therefore the spring is just a convenient way of supporting the bracket.

Yes, but as EFLI said, they can't really have it both ways - they have to decide whether the 'electrical parts' are Class II or not.

If they are Class II, then it doesn't really matter (give or take the undesirability of unnecessarily earthing anything that EFLI has been talking about) whether any metal parts of the fitting ('external' to the Class II 'electrical parts') are earthed or not. However, if they are not considering the electrical parts as Class II, then the entirety of the fitting is Class I, and requires 'adequate' earthing of the exposed-c-ps (and, as I've said) I'm not convinced that the clip qualifies as that!).

Kind Regards, John

 

[ericmark]

I have not got my book to hand, seem to remember there are three types of extra low voltage. With SELV there must not be an earth, there is also FELV and another can't remember the name, one has to be earthed and the other is optional. I can't remember what class II and III covers? Clearly SELV is class III the S did stand for separated.

I remember having arguments over the labels on computers. Most power supplies would be supplied with a spare label to be placed on the computer case, but often this was not done, and the label on the power supply often could not be read once fitted. So the question arose (1) if no label visible should it pass the inspection and testing of in-service electrical equipment? and (2) where a second label is fitted should the details be accepted or should one remove the power supply to read original label?

It seems some imported power supplies were not giving the required isolation hence the question. The computer was earthed, however items plugging into the computer were not, and so these items could it seems allow a user to make contact with a low voltage with no fuse or RCD to protect them, at that time computers were well known for causing RCD's to trip so having a non RCD supply for computers was common.

Today computers are not made up in back streets and we have RCD protection on all sockets so no longer a problem, but the problem did alert me at the time to the three extra low voltage types.

I think lighting has changed due to cool lamps. We would not dream of changing a halogen lamp without turning it off, and even a standard bulb would require ones cap or a glove to stop one being burnt. However today the lamps are cool and for the first time we have been able to change them with bare hands. This means earthing is now far more important, also not having live parts which one can touch, the pineapple shaped lamp was at one time a problem as the LED's did not have an outer globe around them and you could touch live parts.

When modifying lamps the question arises do they need type testing when used by an ordinary person. A consumer unit is a type tested distribution unit designed for where ordinary person is in charge of the installation, but with light fittings we don't have a separate name or other way to work out if the whole unit is type tested. Buy a simple BA22d lamp holder and often there is the double square mark on it as double insulated, however use this to build a table lamp and it does not mean the whole lamp is double insulated.

It comes down to a warranty of skill, the person doing the work should know what they are doing, or simply they should not be doing the work.

 

[JohnW2]

I have not got my book to hand, seem to remember there are three types of extra low voltage. With SELV there must not be an earth, there is also FELV and another can't remember the name, one has to be earthed and the other is optional. I can't remember what class II and III covers?

This is less straightforward than one might think ...

SELV, FELV and PELV ('the other one') have really got nothing to do with Class I and Class II.

The former relates to different types of ELV arrangements, in particular whether any part of the supply (one side, or some intermediate point) is, or is not, connected to the installation's 'earth'. SELV is separated (i.e. isolated) from earth, PELV is not isolated from the installation's 'earth' (i.e. one side, or maybe some intermediate point, is connected to earth) and FELV is rather vaguely defined as an ELV system which does not fully satisfy the requirements for SELV or PELV (whatever that means!).

Class I/II relates to the way in which protection against electric shock is provided - either by earthing of exposed-c-ps or by use of double/reinforced insulation. At first sight, one might assume that this only really relevant if there is LV within the equipment (alone, or in conjunction with ELV), since I thought that the whole idea of ELV was that it was sufficiently low voltage as to pose a minimal risk of serious electric shocks. However, as you go on to say ....

Clearly SELV is class III ...

Indeed, Class III is defined as equipment which provides protection against electric shock by use of SELV. This seems consistent with what I've just suggested - that 'protection against electric shock' is considered adequate if the voltage is low enough to present a risk of serious electric shock. However, that is no less true of PELV and FELV, so I'm not sure that I understand the thinking - and I'm not even sure whether equipment which contains only PELV or FELV has to be provided with additional 'protection against electric shock' as per the requirements for Class I or Class II.

Kind Regards, John

 

[ericmark]

Not got Amendment 3, only the original BS7671:2008 and there is nothing to say extra low voltage is exempt from RCD protection and the 50 mm deep rule. I expect that has changed?

The point is a supply from an isolating transformer can get connected to a live 230 volt supply after it leaves the transformer, a staple could in theory connect a extra low voltage and low voltage supply together. Also running parallel to each other capacitive or inductive links could allow a transfer enough to make one jump. So although touching an aerial may not give you enough of a direct shock to kill, it could cause one to lose grip of a ladder and it's when you are grounded that the damage is done!

In the space between ceiling and floor you can get a collection of wires, and these are not always clipped and some times they have connector blocks or other items which are not as one would hope, even simply pulling a cable too fast can cause friction burns which will allow wires which should be well insulated and have been installed correctly to allow power to reach other wires which should not have any mains power to them.

I know I have snipped alarm cables and removed them from low voltage trunking, much to the annoyance of the alarm company, they seemed to think their cables were immune to friction burns, in commercial buildings we do keep low voltage and extra low voltage separate, but in a house it's not that easy. It does not matter if a ELV cable or a water pipe, if it gets connected to a LV supply there are just one way it can fail safe before some one touches it. And that is for power to go to earth and open a protective device. Be it a RCD, fuse or MCB it needs an earth to raise the current to point where it trips.

Because the human body is a large mass it is likely we will get a shock when touching a live part unless some method is used to raise our body to that potential first. In the main it takes two faults. A door bell wire is trapped under a disused bit of water pipe, and a mains cable is also trapped in some other location under the same pipe, so door bell becomes live. Using metal in partition walls is another way two seemingly independent wires can become interconnected. A plasterers nail, a immersion heater thermostat failing, and no glue on the overflow tun-dish was one well reported death due to interconnected metal parts.

 

[JohnW2]

Not got Amendment 3, only the original BS7671:2008 and there is nothing to say extra low voltage is exempt from RCD protection and the 50 mm deep rule. I expect that has changed?

I don't think Amd3 changed any of that. The regs are, in general, pretty silent as regards the distinction between LV and ELV. However, I've never seen an ELV circuit, per se, being RCD protected, and it clearly would normally be of no value in the case of SELV, and unlikely to be 'life-saving' (given the absence of any appreciable risk to life in the first place) with any sort of ELV (provided, of course, that it remained SELV)....

The point is a supply from an isolating transformer can get connected to a live 230 volt supply after it leaves the transformer, a staple could in theory connect a extra low voltage and low voltage supply together.

Whilst that is true, it is equally true that a staple, nail or whatever could 'connect together' a live LV conductor any anything conductive, the latter not necessarily anything to do with anything electrical. The main point of ELV, particularly SELV, is that it provides protection from serious electric shock by being ELV. If one is going to consider the possibility of it ceasing to be ELV because it becomes accidentally connected to an LV supply, then one might just as well forget about using ELV in the first place.

Also running parallel to each other capacitive or inductive links could allow a transfer enough to make one jump. So although touching an aerial may not give you enough of a direct shock to kill, it could cause one to lose grip of a ladder and it's when you are grounded that the damage is done!

I think you're somewhat scraping the barrel here and, in any event, I don't really know what you would want to do to avoid that theoretical scenario (other than route cables differently) - no protective device would be of any assistance.

Kind Regards, John

 

[utterlydiy]

OK, I'm back with an update.

As previous I had 12 12v - 35w (MR16 -GU5.3) halogen downlight fittings. Each light had a transformer rated at 20 - 60va.

Originally I asked about changing the lamp holders from GU5.3 to GU10 and removing the transformers so that 230v led's could be fitted, but retaining the actual ceiling light fitting.

I have now decided to retain the GU5.3 holders, but still wanting to use 12v led's. As a trial and error I fitted one MR16 GU5.3 12v led lamp/bulb with the existing transformer and it worked. On this I purchase more (B&Q) led's to replace the 35w halogen lamps/bulbs and all 12 worked. But after some 20mins one or two started flashing.

On this as each 12v led lamp/bulb is rated at 4.8w which is below the min 20va rating of the transformer. I have managed without ripping the ceiling etc apart to modify the wiring, so that now one transformer feeds 6 leds in a 12v loop. This giving a rating of 30va (5w x 6=30) which is within the transformer range of 20 - 60va.

But for whatever reason the lights stayed illuminated for 10/15mins then went out, with the transformer being hot.

Why should this be.

thanks

 

[JohnW2]

But for whatever reason the lights stayed illuminated for 10/15mins then went out, with the transformer being hot.

Could you put them back on again after everything had 'cooled down', or are they now 'dead'?

Kind Regards, John

 

[utterlydiy]

Dead, but the trip is intact.

The other six with with their individual transformers are still ok at mo.

 

[JohnW2]

Dead, but the trip is intact. The other six with with their individual transformers are still ok at mo.

Hmmm. I can but assume that either the transformer supplying the 6 lights has, for some reason, blown up (although it's hard to see why it should have) or that there is some mismatch between the voltage being supplied by transformer and that required by the LEDs, such that the latter have been killed.

Do you have a multimeter that you could use to see what, if anything, is coming out of the transformer? If not (or even if yes!), at least try swapping one of the currently 'dead' LEDs with one of those that is still working - to see if the LED is still alive. You could also try seeing if the suspect transformer is still able to work just one of the lights (take lamps out of all but one).

Kind Regards, John

 

[utterlydiy]

I was just going to post.

Still have 230v input when switched on, but 0v on the 12v output no matter whether none or one connected.

 

[JohnW2]

I was just going to post. ... Still have 230v input when switched on, but 0v on the 12v output no matter whether none or one connected.

Dead transfomer, then - but goodness knows why. Are you sure that something has not somehow shorted the output?

Presumably you have 5 more to play with - so maybe worth another try? Perhaps with just one or two of the lamps in, initially, and then gradually plug in more 'if all seems well'?

Kind Regards, John

 

[utterlydiy]

Just checked, with all lamps/bulbs removed. No short/resistance etc is shown on meter on the 12v circuit.

So should I be looking for a driver type transformer for the 6 leds of 30 watts in total, rather than using what looks like to be a voltage transformer.

thanks

 

[JohnW2]

Just checked, with all lamps/bulbs removed. No short/resistance etc is shown on meter on the 12v circuit.

OK

So should I be looking for a driver type transformer for the 6 leds of 30 watts in total, rather than using what looks like to be a voltage transformer.

If the LED lamps are described as "12V", then they must have their own built-in current control and therefore should be fine with a 12V 'voltage transformer'. Have you told us exactly which LED lamps you're using?

Kind Regards, John

 

[utterlydiy]

http://www.diy.com/departments/diall-gu53-mr16-345lm-led-reflector-light-bulb/1324497_BQ.prd