I recently installed a Rheem Retex-18 tankless electric water heater. When I turn the heater on I experience many electrical issues around the house: 1. Sense home energy monitor freaks out and turns off 2. Smart thermostat exhibits a loud buzzing 3. Breaker panel buzzes loudly.
The cable run is about 40 ft, and uses two 8AWG cables and 2 40A dual pole breakers. The heater operates normally, and I even notice that there is very little flickering from lights when the heater is on. I measure a <2VAC drop when the heater is under load. The breakers do not get hot. I checked the ground connection and it appears to be fine. The house has a 200A service, and I live in an area where most houses have electric baseboard heating, so I expect that the service is sized appropriately. Walking the street it seems like every pole pig is serving 3 -4 houses. I tested this both when the temperature outside is hot, and when it is cold, so my local load does not seem to be an issue. I checked to make sure that the cables are not reversed on the heater and they are not. Both elements are recieving each phase in the same order. I tried turning everything in my house off, and just turning the heater on and still experienced the same issue, even with a flow rate low enough to only pull 10 KW. The connections to the breaker, and the breaker to the panel seem to be sound. Panel type is a Eaton CH.
Any idea what is causing this?