When you have a split system HVAC unit, where the air handler mounts on a wall in the room (sometimes over the door.) and the compressor is outside. We know that the compressor needs a disconnect, what about the air handler? Do they have a built in disconnect switch inside of the unit? What if there isn't one, do you need one? What if the circuit breaker is lockable, would that count as a disconnect?
The air handler in mine is low voltage, wired with thermostat wire. I assume the disconnect is the plug. I think I have bigger fans in my PC case. It is about an amp at 24v as I recall. The condenser is 120v listed for a 15a circuit. I put it on the service outlet for my real AC.
My electric water heater on its own 240V 30A circuit, rated 4500W, does not have any disconnect other than the breaker itself. It is hardwired without a plug. Does it need any more of a disconnect? I don't see how this would be any different than the air handler part of the AC, as long as it is at least on its own circuit.
If your referring to a mini-split AC system, all of the systems I have seen for probably the last 15-years get power for the indoor evaporator blower and controls from the terminal board in the outdoor condenser. When you pull the disconnect for the outdoor unit, you also kill power to the indoor unit. I would say that unless you see a requirement for a separate disconnecting means for the indoor unit in the manufactures listed instructions for that particular equipment, you shouldn't need one.
Electric Water Heaters come under Appliances (422.13).Article 422 Cannot have a Plug for a Disconnect unless its portable (422.1 & 422.16) & does require a Disconnect either Within Sight OR capable of being locked (422.30 & 422.31).
Motors AHU's ect come under Article 430. Start with 430.101 & 430.102 (A) & 430.102(B) They do require disconnect switches per theses sections. 430.109 Types of Disconnect switches Approved for use as stated. Except under the exceptions as noted.
You want to look at Article 440, Air Conditioning equipment. Specifically, 440.14.
The disconnect - which CAN be a plug - has to be within sight of the equipment. Now, some might quibble, but to me, this means that the disconnect for the equipment you're working on has to be within sight of that equipment. In other words, if the system has components in more than one location, each location needs another disconnect.
BTW, a point of vocabulary: the part we are discussing is called the 'evaporator.' An 'air handler' is another piece of gear completely. The part outside is called the 'condenser,' and contains the compressor.
430.109 does list a Cord & Plug as a approved disconnect . I stated see 430.109 . 440.13 Cord -Connected Equipment 440.12(D) Disconnecting Means Refers you to 440.12 440.14 Location (within sight ) Same as 430. There is a Exception #1 But for Industral process. Exception # 2 Might interest you . 440.3 A & B Says 430 applys EXCEPT as modified by 440.