Thanks @johnBoy, useful to know.
Everyone, is it true that "no relay" plugs are suitable for monitoring energy use in washing machine, fridge freezer, tumble drier and so on (inductive loads)?
I've read in a couple of places that people are doing this, and also someone saying they'd been advised that in a plug with a relay, it would be fine so long as the relay isn't switched.
All seems questionable, but idk enough myself. If not, what do folk use to monitor power in these cases?
Example:
Bad advice. If the relay is not switched, how would your device get power to be measured? The limiting part of the relays are the contacts themselves.
Some helpful answers here on Mastodon (tldr: people are getting away with relay plugs they don't turn on and off). Also with the Shelly PM Mini, a wired meter without a relay, and there's a link to the Althom no-relay plugs):
Shelly EM mini gen4 is latest energy monitor without relay.
Thanks for the ping (and reccomendation)!
At the time of writing, our provided ESPHome config does not provide a full cumulative total.
This was due to the following:
restore: true being set.But, you can add one via the following config block:
sensor:
- platform: integration
name: 'Total Energy'
sensor: power
time_unit: h
restore: true
state_class: total_increasing
device_class: energy
From experience, is not the most relevant metric; esphome is usually a lot more responsive to telemetry updates out of the box, so I'd recommend defaulting to using the instantaneous power readings graphed in homeassistant.
The daily will work for the energy dash in Home Assistant too, since it's configured to reject negative deltas (eg, resetting to zero).
Tasmota does have it's cumulative counters enabled by default.
We're currently out of stock for UK tasmota, but have a few ESPHome left in stock (not many, hence the generic out of stock across both UK variants, as we'll accept backorders for both).
The next batch is in production as we speak!
Additionally, we have a guide for moving between the two firmware options here - https://youtu.be/Okx1MKVfGlM
Inductive and capacitive loads (motors, compressors, etc.) can be tough on mechanical relay contacts over time. Capacitors cause inrush current on power-on, and inductors cause a voltage spike when switching off, which can lead to arcing and gradual contact degradation. Relay contacts sticking or fusing is the most common failure mode we see in smart plugs.
For a pure monitoring context though, where you're leaving the relay permanently on, this largely isn't a concern as the wear only really happens during switching. If a relay does eventually fail, for something like a washing machine or TV the worst case is that the plug stops passing power and you notice.
We'd still suggest some caution with fridges and freezers, though not specifically because of relay wear. Any unexpected power interruption, whether that's a relay failure, accidental switch or a power cut, can stress the compressor and obviously risks food safety. For those, a monitoring-only solution with no switching capability at all would be ideal (foreshadowing 
)
For everything else, a relayed plug left permanently on is absolutely fine for monitoring use. If you'd like extra peace of mind, Tasmota's PowerOnState 4 will lock the relay on and prevent further switching, and you can also disable control from Home Assistant's UI.
Hope that helps, feel free to shout if you have any other questions!