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I have an SSR in open state, split phase 220 across the inputs (heater inline), for now ground is not connected to anything, but I noticed, I have ~6.5 VAC from the heat sink to ground. I checked and there is no path the multimeter can find between either input terminal and the heat sink. What is causing the heat sink to be hot with low AC voltage? Is it safe to just ground the heat sink to bring the 6.5 VAC down? I can’t just leave the heat sink floating because I want to mount it to a conductive chassis that we need to handle.

It’s a bit of a knock off relay, but I’ve seen this now on two separate systems (same brand but different relays) in two different buildings. Doesn’t happen with just 120 VAC across the inputs. For both instances, the relays still open and close fine and are currently operational with 220 split phase and 120.

SavageHenry11
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  • Welcome! Datasheet of SSR? Capacitive coupling and voltage division? Can you turn everything off and measure the resistance between it and ground? – winny Mar 21 '23 at 22:08
  • it's too far on knock-off side of the spectrum to have a data sheet here is the link: https://www.amazon.com/Inkbird-Solid-Thermostat-Temperature-Controller/dp/B01MCWO35P/ref=sr_1_3?keywords=ssr&qid=1679436604&sr=8-3 the resistance is not measurable when in open or close from inputs to heat sink. – SavageHenry11 Mar 21 '23 at 22:11
  • No datasheet = no sale. – winny Mar 21 '23 at 22:15
  • Agreed, I have a nice one coming tomorrow from mcmaster, Was just wondering if there was a known mechanism for where the weird voltage was coming from. – SavageHenry11 Mar 21 '23 at 22:21
  • Best guess, tiny leakage current and high impedance input on your multimeter. – winny Mar 21 '23 at 22:24
  • Ok I just gave the heat sink to ground and nothing heated up or shorted, you're probably right about the small leakage current. – SavageHenry11 Mar 21 '23 at 22:47
  • 6.5 VAC is not a positive voltage – jsotola Mar 21 '23 at 23:40

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Parasitic capacitance between the electrically hot internal semiconductors and the isolated SSR baseplate causes this. You can prove this by placing a 10k resistor across the high impedance voltmeter and the small potential you measured will disappear. These currents at powerline frequencies are safe to go to ground. At much higher frequencies like switch-mode the currents can cause issues.

winny
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Autistic
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