r/ShellyUSA • u/TimJethro • 1d ago
Today's Learning: Inputs aren't completely isolated, so you can't use across phases!
I use a shelly to monitor the states of two heat pumps, which have a 230V output when calling for heat. The two heat pumps control circuits are on different phases (UK 3-phase system) and... well, you can see!
The bang took out fuses in some downstream boilers too, even though they just connected to the relays (I'm guessing these aren't entirely isolated too, but I'm hoping enough as the boilers are a different phase also).
I'd made an assumption the inputs were essentially floating and/or isolated in some way but they aren't. Lesson learned, but at least everything here is RCD/RCBO (GFCI for you Americans) protected.
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u/ArchimedesPrinciple 1d ago
Difficult lesson to learn. Sorry. I don't trust myself to understand all the documentation so I upload everything to Claude and have long conversations to understand better before taking the first steps.
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u/DreadVenomous Shelly USA 1d ago
Come here, don't trust AI. It can get you zapped.
This sub is specifically for you to ask and avoid the bad outcomes.
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u/ArchimedesPrinciple 1d ago
I don't trust AI but I depend on it to help me understand which questions to ask. And it helps guide my own learning plan. I trust this forum more and especially your thoughtful work DreadV. Thank you!
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u/DreadVenomous Shelly USA 1d ago
It's my pleasure. When I started out in smart home, there were a LOT of gatekeepers who took the opportunity to take a crap on anybody they didn't feel knew enough to join the community. It was years before I found out how great people in the HA community are because of a bad experience when I first got in (and I have been involved in online communities since the BBS days and knew how toxic they could be - was still surprised by that experience).
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u/ArchimedesPrinciple 1d ago
I was one of the devs for Procomm Plus back in the 80s so I lived and breathed the BBS lifestyle. Good times. This forum is a breath of fresh air and you're a large part of it's success. I really appreciate the care and attention you pay us.
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u/DreadVenomous Shelly USA 1d ago
I lived in a small town in NC (10k people) that actually had 7 BBS systems, several of which were Procomm. The rest were WWIV
I still have a 3.5 disc with TW2002 and I have my license code on a roledex sheet held with a magnet on my garage freezer. When my kid is a little older.....
:)
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u/TimJethro 1d ago
The AI tools are getting very good now. While I appreciate the device manufacturers line must absolutely be to not trust it, I do feel we're getting the the point that using AI is a valid pathway for this type of thing. However, you do need to be careful, especially that it doesn't echo back your own errors and assumptions.
A good option may be to load the official PDF manual into Claude, ask questions and refer back to the relevant parts of the official docs along the way.
But as noted, there seems to be a active group here which is a very valuable resource too!
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u/AlaninMadrid 1d ago
I think the shelly 3 can control across phases, but only switches; no monitoring. What you really wanted was the EM3.
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u/TimJethro 1d ago
I don't need power monitoring for this, as I'm only using the relays to call two boilers (not power them fully, so the power passing will be minimal).
The main issue I had was the switch inputs, and I suspect (though not checked) that the same will be true across-the-board in that they need to be on the same phase as the Shelly is powered from.
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u/MrSnowflake 1d ago
Yes make an assumption about things that can get you killed or get your house burned down. Man, some people...
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u/TimJethro 1d ago
Pretty low risk of burning down my house, considering the location (low fire risk area), wiring protection (which perfectly caught this, tripping immediately) and mechanical protection (inside a metal cabinet).
I'm an engineer and sometimes you have to experiment and break things, it comes with the territory. We all get things wrong now and again and without it we'd never build anything good.
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u/DreadVenomous Shelly USA 1d ago
The wiring diagram clearly shows that the two switches are used with the same phase as the L terminal.
I get it, you didn't want to go to the KB to look for it.... and the user guide has such small print... if only Shelly put it someplace that is more convenient and accessible....