said by Jack_in_VA:Not really, since it's not a requirement to use SOOW cable for vibration-prone devices, just a recommendation to prevent wear on cable. The use of THHN though is a requirement (same requirement where you can't use SJT or lamp cord to wire outlets). said by sk1939:
Simply because you have to use solid wire (romex or THHN) or stranded THHN to connect hardwired appliances (non-vibration) or using SOOW if it is a piece of vibrating equipment (like a motor).
Really? In 52 years of electrical work I've never heard that. Looks like my Heatpump is out of compliance and illegal. It has Romex to the pull out disconnect but THHN stranded to the unit which definitely vibrates and has a motor (Compressor).
As far as the water heater I can sit it in the yard and wire it up with a portable cord to the generator and use hoses to connect the water to the house.