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I would like to build a sous-vide circularor, using a PID-controlled immersion heater. I've read that as the product wears out, there might be some electricity leakages, so I would like to make the apparatus safer.

Here is what I thought about:

enter image description here

Two electric wires are submerged together with the water heater, and connected to one side of a normally closed relay. When there is electricity leakage, the relay commutes the switch on the other side, killing the power to the heater.

Would this work? Do you have a better way of making the device safe(r)?

Finally, what should be the specs of the relay I should buy? I really don't have a clue of what voltage would flow in, say, tap water, during a leakage. Thank you in advance, please take into account when answering that I'm a complete electricity-amateur.


Edit: the power supply are L+N

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  • \$\begingroup\$ Your drawing shows a DC supply. Is it DC or mains (live + neutral / L+N)? \$\endgroup\$
    – Transistor
    Mar 13, 2021 at 22:37
  • \$\begingroup\$ L+N @Transistor \$\endgroup\$
    – Leonardo
    Mar 13, 2021 at 22:39
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    \$\begingroup\$ Use an immersion heater with a metallic outer tube, and ground that. (There should already be a grounding tag on it as well as 2 for power) Then an RCD or GFCI will provide safety with nothing else needed. \$\endgroup\$ Mar 13, 2021 at 23:06
  • \$\begingroup\$ @BrianDrummond Just so that I make sure I understood: I take a wire, one end is attached to the tube, the other one to the ground wire of the power cord? \$\endgroup\$
    – Leonardo
    Mar 13, 2021 at 23:12
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    \$\begingroup\$ You shouldn't need to attach a wire to the tube. There ought to be a tag with a GND symbol on it, already connected to the tube. \$\endgroup\$ Mar 13, 2021 at 23:13

3 Answers 3

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  • The immersion heater element tube should be connected directly to mains earth.
  • If mains powered the heater should be protected by an RCD/ELCB/GFCI (depending on where you are located).

In this way any leakage will flow to earth, the metal parts will stay at a safe voltage and the circuit breaker will trip.

Your proposed solution won't work and wouldn't be fail-safe if it did as it relies on the relay engergising to make the circuit safe.

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  • \$\begingroup\$ So, I should attach a wire's end to the heating element, and the other end should be attached to the earth wire of the power cord (providing supply to the system)? \$\endgroup\$
    – Leonardo
    Mar 13, 2021 at 22:58
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    \$\begingroup\$ @Leonardo No. the heating element connects to live and neutral. The metal case of the heater connects to earth. The heater should have three connections, for live neutral and earth. If it doesn't, get one that does. \$\endgroup\$
    – Simon B
    Mar 13, 2021 at 23:22
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    \$\begingroup\$ @Leonardo: You are way out of your depth on this if you think that one wire of the heating resistance should be connected to earth. Please seek help from someone who understands mains wiring, proper earthing and circuit protection. Mains electricity and water are a lethal combination. Your comment here shows that you lack the knowledge to do this safely. \$\endgroup\$
    – Transistor
    Mar 13, 2021 at 23:37
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Please get a safe water-heater and not a cheap no-brand. A proper waterheater should not have any risk of leakage current unless it is severly damaged.

There are also purpose-built fuses that measure that the current on both phases are identical. Use those. Don't try to DIY saftey mechanisms unless you are really sure of what you are doing.

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    \$\begingroup\$ Fuses can't measure balance. You mean RCD/ELCB/GFCI circuit breaker. I think it's worth fixing. \$\endgroup\$
    – Transistor
    Mar 13, 2021 at 22:50
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Would this work? NO
Do you have a better way of making the device safer?

Only use a Stainless Steel sealed heater that is earth ground protected.

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  • \$\begingroup\$ Unfortunately such heaters are unavailable in Europe: would a US heater (that's intended for 120V) work at 230V too? Otherwise, grounding a non-grounded heater, is this a job an electrician would make? \$\endgroup\$
    – Leonardo
    Mar 14, 2021 at 9:19
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    \$\begingroup\$ @Leonardo No. A 120V one will overheat and burn out. 230V heaters are definitely available - I have one. It's intended for heating a jug of water to make tea, and came with a British 3-pin plug on the end. Because it needs 3 wires. \$\endgroup\$
    – Simon B
    Mar 14, 2021 at 11:52
  • \$\begingroup\$ I'm seeing on Internet the same models sold to Italy with a two pin plug, but to UK with a 3 pin plug. Is it possible that having a 3 pin plug doesn't necessarily imply being grounded? Also, it would very appreciated if you could share with me the model of your grounded heater, or a link to the advertisement (if this doesn't violate the rules of stack exchange) \$\endgroup\$
    – Leonardo
    Mar 14, 2021 at 12:13
  • \$\begingroup\$ Double-electrically insulated can be ungrounded yet have more thermal resistance. \$\endgroup\$ Mar 14, 2021 at 14:44

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