It's incredibly difficult not to have a small amount of leakage - not to earth but to the incoming supply. Medical grade power supplies manage to it down to a possibly unmeasurable level, but yer average LED supply will have a very slight leakage path from the incoming supply, whether through the interwinding capacitance of the isolating transformer, or even semi-deliberately through EMC suppression capacitors. So anything connected to an "isolated" mains supply will typically float to somewhere around half the supply voltage.

The question is, how much current is available / what is the source impedance. A meter may measure 80V, but that doesn't mean that anything more than a minute current can flow.

I'm on my home computer rather than my work computer at the moment, so haven't got access to standards, but from a quick Google (so no promises this is correct!):

Section 13 “Leakage current and electrical strength at operating temperature” of IEC 60335-1-2020 specifies the following maximum allowable leakage currents for major types of household electrical equipment:

for class II appliances and for parts of class II construction – 0,35 mA peak;
for class 0 and class III appliances – 0,7 mA peak;
for class 0I appliances – 0,5 mA;
for portable class I appliances – 0,75 mA;
for stationary class I motor-operated appliances – 3,5 mA;
for stationary class I heating appliances – 0,75 mA or 0,75 mA per kW rated power input of the appliance with a maximum of 5 mA, whichever is higher.

Incidentally, when I am on my work laptop, which is a very reputable brand with a metal case, I'm able to feel a distinct "tingle" when I touch the lid when it's plugged in to its SELV supply! It's fine, it's meant to be like that, but probably does measure about 115V to earth. But can't source any real current.

Of course, if switching your meter to mA shows currents above the above (hopefully followed by a trip tripping!) then the LED supply / transformer is not healthy...

Cheers,

Andy

The Guide to Electrical Installations in Medical Locations elucidates the phenomenon of leakage currents, which result from capacitive, inductive, or resistive coupling of electrical devices. It expounds that no insulator is flawless, and thus every electrical device is prone to some leakage current. It also illustrates this with the example of a laptop chassis, which can exhibit up to half the main’s voltage between the accessible conductive parts and earth, when measured with a high impedance voltmeter. However, the guide wisely cautions against attempting this experiment.

The latest (5 th Edition) of the IET Code of Practice - In-Service Inspection & Testing of Electrical Equipment has a flat limit of 5 mA for AC leakage current.

Previous editons of the Code of Practice had leakage current limits similar to, or the same as, the ones you have reproduced from IEC 60335.

Hi Andy, 

Your laptop PSU has an earth, whereas this LED driver has no earth, only live and neutral.

Can the same leakage occur from the secondary side of the power supply? 

What's important here is that it's not "leakage to earth" (in the sense that I think you're thinking about it), it's an impedance to the supply. Since the supply has some path to earth, the circuit is supply > leakage > earth > direct or leakage path back to supply.

Or to put it another way, if you connect two 1Meg resistors in series, connect one to 240V live and one to neutral, the middle will be somewhere around 115V to earth (because neutral is, you hope, somewhere close to earth). And that's probably what you're seeing.  

What's important here is that it's not "leakage to earth" (in the sense that I think you're thinking about it), it's an impedance to the supply. Since the supply has some path to earth, the circuit is supply > leakage > earth > direct or leakage path back to supply.

Or to put it another way, if you connect two 1Meg resistors in series, connect one to 240V live and one to neutral, the middle will be somewhere around 115V to earth (because neutral is, you hope, somewhere close to earth). And that's probably what you're seeing.  

So in this instance, the leakage is via the frame/chassis of the fixture? 

All components inside should be isolated, but can understand that impurities can lead to discharge. I guess here the leakage is via the secondary side of the SELV transformer?