Has anyone seen those brand new water heaters that are instantaneous and they need 3-40 amp feeds? What do you do about a disconnect within 50' and/or within eyesight?

I suppose they could pull a properly sized feeder and install a small subpanel to an area within sight of the equipment, then run the needed branch circuits to the water heater from there.
One thing though… I know that the SQD QO 6/12 circuit panels I have are only rated at 100A, so not sure if they are available with a higher ampere rating.
If not, then one possible problem might be if the feeder were sized only as needed for the water heater loads but, a larger panel was install installed because of the needed higher ampere rating. Someone else could come along later and run additional circuits out of it to feed other loads.

I'm working on the same thing, in richmond ca, trying to find a small robust panel on opposite side of wall in 1100 sq. ft house, and not have to put in a 20 space panel for 6 slots?

I saw some 6/12s on the SqD site but they are more expensive than a 20/40.

The OCP for the subpanel will prevent the feeder from OL. I seem to remember a GE panel that was 125 amp rated buss.

How about a contactor in a small panel with a push button/switch by the heater?

How about a lock out on the service panel?

If you have a sub panel within sight of the water heater that can be your disconnect.

Is that 3 separate heaters turning ON separate times, or all three turn ON at the same time?

I bet that will dim the lights every time it turns ON. Wouldn't that be annoying? Have you informed the customer on the possibility of the lights dimming?

Greg,

I agree that if there is a sub panel or service panel within 50/eyesight, then we would meet the code. However the service is in the basement and the house is finished, and they install a new water heater in the laundry room, Now what? Could you accept a lockable breaker(s) for the disconnect? Install a sign on water heater stating that the heater has multiple feeds?

This might be the compelling reason to put the sub panel near the water heater.
I know the code allows lockable breakers, how many homeowners actually understand LOTO procedures or have the proper equipment?