Domestic rental, 18 downlighters stopped working

[ericmark]

But the voltage to earth can be 230 volt so insulation must be able to stand that voltage.

 

[ebee]

what John means Eric that the voltage difference to each light is about 12v it is just their references that are different, like the xmas tree lights we`ve used since the year dot. just a volt or three across each one or whatever, the two ends that are 240v apart would not know it, just the number that can be simultaneously touch, and if the insulation holds then nobody would know.

If you stacked a thousand button cells up in a tower fashion, one hand would not know it, two hands a distance apart might get a message

If nothing is earth referenced then who would know?

 

[ebee]

solder a long stick of button cells together, hold it in the middle with one hand, then throw it to a pal, if he catches it with two hands then he might decide not to be your pal.
There I have invented a new game - Catch The Stick

 

[SUNRAY]

But the voltage to earth can be 230 volt so insulation must be able to stand that voltage.

That's a perfectly valid point as I did measure 230V between the metal of the fitting and the bulb contacts.

 

[JohnW2]

But the voltage to earth can be 230 volt so insulation must be able to stand that voltage.

Only if each individual light 'knows something about earth', which they won't if they ae Class II.

If 'earth' does not come into the equation as far as the lights are concerned, you might as well say that, for example, their insulation has to be able to 'stand' about 10,770 V, since some of the lights will be at that potential relative to an (irrelevant) 11,000 V overhead line

 

[JohnW2]

what John means Eric that the voltage difference to each light is about 12v it is just their references that are different, like the xmas tree lights we`ve used since the year dot. just a volt or three across each one or whatever, the two ends that are 240v apart would not know it, just the number that can be simultaneously touch, and if the insulation holds then nobody would know. ... If you stacked a thousand button cells up in a tower fashion, one hand would not know it, two hands a distance apart might get a message ... If nothing is earth referenced then who would know?

Exactly - but it is now seemingly being said that lights were probably Class I, with ';metal parts' that were connected to earth. If that is the case then eric would be right in saying that the insulation between the functional parts of the light and anything earthed would have to be able to withstand something approaching 230V for some of the lights.

Mind you, I tend to laugh a bit about the excitement that often exists about 'voltage ratings', since almost any credible thickness of the sort of materials we use as insulators will withstand very high voltages - for example, things like 'signal cables' that are 'rated' at, say, "50 V" will usually show unmeasurably high IRs even when tested at 1,000 V

Kind Regards, John

 

[ebee]

Indeed if they were class 1 then "If nothing is earth referenced then who would know?" would not apply but if they were class 2 then" If nothing is earth referenced then who would know?" would apply

 

[SUNRAY]

Mind you, I tend to laugh a bit about the excitement that often exists about 'voltage ratings', since almost any credible thickness of the sort of materials we use as insulators will withstand very high voltages - for example, things like 'signal cables' that are 'rated' at, say, "50 V" will usually show unmeasurably high IRs even when tested at 1,000 V

Kind Regards, John

But then do a squarewave ac test at 1KV and see what happens

 

[JohnW2]

But then do a square wave ac test at 1KV and see what happens

I don't have the means of doing that - but what do you think would 'happen' (and why?) - and what sort of frequency did you have in mind?

What I have done is apply 'mains' (i.e.230-240 V at 50Hz) between cores of one of those '50V rated' cables, and have been unable to detect even the slightest of current flow.

 

[Harry Bloomfield]

But then do a squarewave ac test at 1KV and see what happens

Nowt would happen, unless the cable were faulty.

 

[JohnW2]

Nowt would happen, unless the cable were faulty.

That's would certainly be my expectation, which is why I look forward to hearing what he thinks might 'happen'!

 

[Ragnar_AT]

I‘d assume the lights were designed to be class 3 run by a 12 V safety transformer.

 

[JohnW2]

I‘d assume the lights were designed to be class 3 run by a 12 V safety transformer.

Indeed. Although 'assuming' is always dangerous, I would think such to be by far the most likely situation - so, as I've said, if they are designed to run off 12 V and if there is no 'earth' (nor any LV live connector) present at the lights, then there would be no need for insulation in the lights to be able to withstand more than about 12 V (although, as I've also said, I'm sure that, in practice, it could 'stand' and awful lot more than that!).

 

[ericmark]

Clearly if class 3 it is not class 2, I am sure in most cases single insulated would not cause a problem, however as electricians we know the rules, and accidents do happen, so not worth taking a risk and one would want to watch my back and some way write down the need to correct in some sort of report.

 

[SUNRAY]

Of course I now regret not taking pics, these are a very open construction using white coated 15-20mm wide metal with a see-through JB on the top offset to one side and below that a GU5.3 socket on a crossbar, the wiring is in a very bulky braiding silicon sleeve. Below the bulb is a clip. I didn't really pay too much attention to detail as My initial faulting approach was aimed at checking the switching as that is where the other company had diagnosed the fault and changed 2 switches, for all I know one of which could have been faulty.