Should my LED strip heatsink connected to EARTH or DC GROUND - Page 1
Forum section: electronics / projects

author: drakejest
author_rank: Regular Contributor
timestamp: January 24, 2021, 10:33:34 pm
content: So i am attaching led strips, and it so happens that there is a convinient metal surface i can attach it too that will be perfect at the same time as a heatsink. Now i am not sure if i should connect it to EARTH or the DC GROUND (0V).The led strip is powered by a 12v powersupply that has Live, Neutral, Earth as its inputs and 12v(+), ground (-) as its outputs. I am confused if the metal heatsink should be earthed or grounded ?

author: fordem
author_rank: Regular Contributor
timestamp: January 25, 2021, 02:12:20 am
content: Why connect it to either? And whilst I'm asking questions, why is connecting it to 12v(+) not an option?How will the LED strip be attached to the metal surface? Once the strip is attached, will there be any continuity to the metal surface? The answers to these last two questions could actually be the determining factor to the question you're asking.The last two 12V powered LED strips I installed were held by adhesive strips (the LED strips came with the adhesive pre attached) and no electrical connectivity to the mounting surface - one ended up being stuck to an aluminum channel - the other to a wooden surface, because there is no electrical connectivity between the LED strip and the surface, I've paid it no mind.

author: james_s
author_rank: Super Contributor
timestamp: January 25, 2021, 06:03:20 am
content: Typically you want any exposed metal of mains powered devices connected to earth, which may also be tied to the DC ground in many cases. If a fault causes the metal to become energized the ground will shunt the current and cause the circuit to trip, that's what the ground is for.

author: Berni
author_rank: Super Contributor
timestamp: January 25, 2021, 07:33:34 am
content: Exposed metal surfaces should always be connected to Earth.If the metal object is connected to something else, or floating, then there is a possibility of a fault that connects live 220V to it. This means touching it could be lethal. But if its connected to Earth any voltage that shorts to the metal object gets diverted to Earth and/or tripping the RCD breaker to shut off the power.

author: drakejest
author_rank: Regular Contributor
timestamp: January 25, 2021, 01:18:02 pm
content: Quote from: james_s on January 25, 2021, 06:03:20 amYes that is exactly what want to avoid, incase something happens the metal wont be energized.The strip wont be electrically connected to the metal heatsink (under normal circumstances) but i dont know if i should tie the the metal to earth or dc ground

author: james_s
author_rank: Super Contributor
timestamp: January 25, 2021, 06:42:43 pm
content: Tie it to earth ground. Any exposed metal should always be tied to earth ground. DC ground is for carrying current, earth ground is for safety. Always.

author: TheMG
author_rank: Frequent Contributor
timestamp: January 25, 2021, 07:30:42 pm
content: If the 12V power supply powering the LED strips is the isolated/double insulated type, there is no need to connect the metal that the LED strip is attached to ground or anything from a safety standpoint (this may vary by country).There may, however, be EMC considerations if for instance the power supply is unfiltered or you're using high frequency PWM to drive the LEDs, where connecting the common terminal of the power supply output to the metal backing could help reduce EMI.

author: Zero999
author_rank: Super Contributor
timestamp: January 25, 2021, 08:01:15 pm
content: Quote from: TheMG on January 25, 2021, 07:30:42 pmYes, there's no need to connect the metal heat sink to earth, if it's run off a double insulated power supply. If the power supply meets the relevant EMC standards, there should be no need to earth anything. It will have the required filtering an Y capacitor, to keep EMI within the legal limits.Contrary to what many have stated in this thread, there's no requirement to earth all exposed metalwork. There are plenty of, perfectly safe, double insulated appliances, with unearthed, exposed metallic surfaces, on the market. They're designed so that all the live parts are double insulated from the metalwork. An example is a double insulated mains electric drill, with a metal chuck, which has some plastic gears/shafts in the the drive chain, to provide an extra layer of insulation from the motor's frame, which will be encased in plastic, even if there are other metallic parts on the case.

author: Monkeh
author_rank: Super Contributor
timestamp: January 25, 2021, 08:07:11 pm
content: Quote from: james_s on January 25, 2021, 06:42:43 pmThere's no need to tie exposed metal to earth if it's not in danger of becoming connected to a dangerous potential.

author: drakejest
author_rank: Regular Contributor
timestamp: January 26, 2021, 02:15:31 am
content: It would seem that the power supply is the critical factor here,Power Supply 1Power Supply 2How do i check if its double insulated or not ?

author: viperidae
author_rank: Frequent Contributor
timestamp: January 26, 2021, 05:49:52 am
content: None of those are double insulated. You probably find the case is grounded, hence the ground terminal in the mains side.

author: drakejest
author_rank: Regular Contributor
timestamp: January 26, 2021, 07:35:45 am
content: Quote from: viperidae on January 26, 2021, 05:49:52 amWith that said, so the the metal heatsink of the led strip should be tied to EARTH then ?

author: Zero999
author_rank: Super Contributor
timestamp: January 26, 2021, 08:47:16 am
content: Quote from: drakejest on January 26, 2021, 07:35:45 amIt's not necessary to earth the heat sink. Meanwell is a decent brand. The output will be properly isolated from the mains.

author: Berni
author_rank: Super Contributor
timestamp: January 26, 2021, 10:25:15 am
content: Quote from: Zero999 on January 26, 2021, 08:47:16 amStill even the best medical grade power supply in the world wont protect you if the mains cable coming in gets chewed up against a metal surface or the thing gets wet and similar.In a lot of cases earthing might not be mandatory. For example TVs here in Europe commonly come with 2 prong plugs without earth, yet its perfectly possible to touch the TVs internal ground rail by touching the shield of the RF connector or the RCA connectors. Same thing for phone chargers, none of them has earth.But if you already have an earth conductor coming in then it is worth the extra 2 minutes of effort to actually connect it to exposed metal. There is no downside to connecting it, only the upside of being more safe in the event of a mains fault. There are cases where earthing can cause issues with ground loops like in audio equipment (low voltage analog signals between devices), but this is not one of those if its just a LED light.EDIT: And the last part about ground loops is only the case if you also tie together GND and Earth as it is commonly done for safety. In your case this also doesn't matter unless you can actually touch the LED wiring from the outside.

author: drakejest
author_rank: Regular Contributor
timestamp: January 26, 2021, 12:10:51 pm
content: if i tie the shield to earth, and a damaged GND wire touch the metal sink then nothing would likely happen, but what about if a 12v touch the earthwont that be a short circuit?

author: Berni
author_rank: Super Contributor
timestamp: January 26, 2021, 12:27:39 pm
content: Quote from: drakejest on January 26, 2021, 12:10:51 pmNo because the outputs of these PSU modules are typically floating, so GND and Earth are not connected together inside.So if the +12V wire touches the earthed heatsink that simply makes the DC side of the power supply float with its GND at -12V in comparison to Earth. So then the voltage between +12V and earth is 0V, voltage between Earth and GND is -12V and voltage between GND and +12V is still 12V so the LEDs keep working.The short you described only happens if you also externally run a wire between the GND and Earth terminals.

author: drakejest
author_rank: Regular Contributor
timestamp: January 26, 2021, 12:36:40 pm
content: It maybe important to note that none of the power supply metal casing will be touching this metal heatsink, the powwer supply will be placed in a different location and there will be 2 wire( 3 if i decide to ground the heatsink) to the LEDS.SOOOO.... I should EARTH the heatsink, the time/cost is neglible, I am more concerned on safety/perfomance for anybody who will do maiintinance in the future

author: Zero999
author_rank: Super Contributor
timestamp: January 26, 2021, 12:52:40 pm
content: Quote from: Berni on January 26, 2021, 10:25:15 amThat'll only happen if the mains cabling is near the metal surface and isn't appropriately insulated and mechanically protected from it.Quote from: drakejest on January 26, 2021, 12:36:40 pmNo don't bother, just run two wires to the LED. There's no mains near the LED, thus no need to earth anything. The LED being powered off SELV (Separated Extra Low Voltage) is a class 3 appliance and therefore doesn't need to be earthed.https://en.wikipedia.org/wiki/Appliance_classes#Class_III

author: themadhippy
author_rank: Super Contributor
timestamp: January 26, 2021, 01:14:33 pm
content: simple question,in the event of a fault condition can the heatsink come into contact with voltages that are dangerous to people or livestock? if yes earth it and treat it as PELV supply, if no dont bother and stick with SELV

author: Berni
author_rank: Super Contributor
timestamp: January 26, 2021, 01:53:36 pm
content: Ah the power supply is elsewhere.Then yeah don't bother with earthing since it requires a good deal of extra effort. I thought the PSU is next to the LEDs and in that case grounding would be easy to do using a tiny few cm piece of wire.