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Help thinking about Grounding/Safety for LED device

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jai.whitey:
Hello - I'm creating an LED device and I'd like to have a good understanding of grounding/safety so I don't accidentally harm my users!

I'm powering my device with an AC/DC wall mount adapter that outputs 20V which connects to a barrel jack on my PCB. I'm using an LED driver as well that outputs 700mA constant current. My LED itself has a forward voltage of 17.2V at 700mA at test temperature (85C).

I connect to my LED with wires off-the-board. I'm using screw terminal blocks on the PCB itself as this seems to be the most secure connection. And I solder my output wire leads to the LED for a secure connection.

However, I'm using aluminum for the light stand/enclosure itself and I'm worried one of the LED hot wires could potentially become disconnected from the LED and then make a connection to the aluminum enclosure, giving it a voltage potential. And then when a user touches the device, they could become shocked.

How can I make sure nothing catastrophic can take place? My understanding is that to ground a device, a wire from the metal enclosure should be connected to the ground plug in the AC plug, so if the enclosure gains a voltage potential, it will be dissipated through the ground wire.

However, in my case I'm using the AC/DC wall mount adapter so I'm only dealing with DC within my device.

As you can see, I'm a novice so any tips or pointing me in the right direction would be much appreciated.

tooki:
20V is not a shock hazard. You can touch 20V and won't feel a thing. (FYI, around 60V is where safety starts to become an issue.)

So if there's no mains power inside, then grounding the enclosure is not necessary for safety.

What I would do, of course, is make sure the wires are well secured, since you want the thing to be reliable. In particular, where stranded wire is soldered tends to be a weak spot, so that end needs to be supported well.

jai.whitey:
Thanks a lot. Can you explain this more? Even with DC power, say the positive wire to the LED becomes detached somehow, wouldn't this represent a hot voltage of 20V or whatever voltage my driver is outputting. If I touch it, wouldn't the electricity want to flow through me to the earth ground? As you say, 20V is not shock hazard but at higher voltages this would be dangerous?

Benta:
Agree with tooki, electric shock is not a hazard here.

What you do need to look at is fire hazards, eg, what happens if something is shorted or broken or gets too hot somewhere; and that can be quite challenging to analyze.

tooki:

--- Quote from: jai.whitey on October 19, 2021, 06:29:00 pm ---Thanks a lot. Can you explain this more? Even with DC power, say the positive wire to the LED becomes detached somehow, wouldn't this represent a hot voltage of 20V or whatever voltage my driver is outputting. If I touch it, wouldn't the electricity want to flow through me to the earth ground? As you say, 20V is not shock hazard but at higher voltages this would be dangerous?

--- End quote ---
Technically speaking, at 20V a tiny bit of electricity could flow through you to ground. But it's such a minuscule amount of current that it simply does not matter. You wouldn't feel it and it wouldn't harm you.

By the international IEC standards, DC under 120V and AC under 50V is considered extra-low_voltage and poses low risk of electric shock. Your 20V DC is far below that. (You'd feel 120V DC, but it wouldn't hurt you.)

Honestly, the biggest thing you can do to ensure customer safety is to buy top-quality wall adapters. The only situation where I could see your product becoming hazardous would be if a) a wire shorted to the metal case, AND at the same time b) the wall adapter failed in an unsafe way that put mains on its output. You're entirely responsible for a), but it's easy to do. The power supply manufacturer is responsible for b), so your responsibility is simply to include a quality wall adapter. That means not buying no-name stuff from Alibaba. Even a "budget" name brand like Mean Well will be perfectly safe.

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