The Shelly EM looks like a very impressive device. It is shown to be installed within a metal fuse box/circuit box. Since the box is grounded, how does the WiFi signal propagate out of the box? I would think that a connection would be needed to a remote antenna mounted outside the box. Yet there is no option on the Shelly EM for such an external antenna connection. Is this a major limitation for the EM, or am I missing something here?
I have not tested one in an enclosed metal box, but you’re right, the signal would be attenuated significantly.
For my use-case I have the Shelly EM mounted in a waterproof box outside of the meter-box with a pipe containing the CT cable running into the meter box.
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I would gather the installation would have to meet electric codes in your area. (Please check your electrical local codes) it would have to be mounted in a connected electrical box (plastic, pvc or fiber box), as any metal box would act as a FARADAY cage for radio waves.
I have one coming and wanted it hand before getting the other hardware for mounting it.
Check the insides here:
There is an antenna connector on there [looks like U.FL] so you could break it out into an external one, if need be.
I would definitely put the EM in a box as it is too easy to touch a live screw terminal.
There is a discussion here on the 1PM where a Shelly rep responded, but it’s not clear whether the antenna I-PEX MHF connector is enabled by default or whether it needs a capacitor moved to enable it like on ESP32’s.
Your approach seems reasonable. Thank you.
I am a bit surprised that Shelly does not offer this advice. Their representatives just respond that the signal is degraded, but it is not a problem if the AP is sufficiently close. This does not strike me has a reasonable response on their part.
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Seems completely reasonable to me. It’s true, is it not? Signal strength will be weaker, but if it’s close enough, then it doesn’t matter. They can’t tell you with any certainty if it will work or it won’t, so giving you an assurance either way wouldn’t be wise.
You could do a “test run” with a small device that has wifi [eg a phone]. Stick it in there and if it stops pinging when you close the box up then the Shelly EM probably will stop working too.
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I did a bit of checking on a Shelly 1PM that I have here.
The RF connector which attaches to the antenna which is wrapped around the case, is not the common Hirose U.FL type, it’s smaller again.
The Hirose U.FL is stated as being 2mm in diameter while the one on the board is roughly 1.1mm in diameter and I’m not even sure that it’s a W.FL type either as W.FL is 1.4mm.
Exactly. I don’t have a (imho overpriced) shelly em installed in my metal fuse box but just a (I think even more accurate) $20 setup made with a d1 mini and 3 pzem004t v3. The wifi AP isn’t to far and the connection is stable - never bothered to check if I could improve the signal. 
With such a setup the d1 mini can also easily swapped for a esp32 with ethernet to have a wired connection. 