Electrical – Can the home’s power supply handle this tankless water heater

circuit breakerelectricalelectrical-paneltanklesswater-heater

So my home was built in 1960 and 15-20 years later another room was added on. There are panel boxes everywhere ha. I have mapped it all out and isolated almost everything. Anything that is unidentified must not be important or no longer existing because nothing seems to lose power when I flip these breakers off.

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The big question…

I have in my possession this electric tankless water heater:

https://www.ecosmartus.com/product/ecosmart-ECO-27-27-kW-Electric-Tankless-Water-Heater

It states that it has an amperage draw of 113amps and at the panel box It will need to have (3) independent 40 amp 2-pole breakers.

You will see in my layout that on Panel A left side I have a 70amp, 30amp, and 40amp breaker that are now obsolete. Can I use those 3 spots to accommodate the new heater?

From my understanding the amperage specifications for an appliance are normally 20% higher than what it actually draws and that most appliances may draw that amount at the initial start up but after that draw much less to maintain operation. I am having difficulty getting a straight answer out of technical support though.

Will I be pushing my limits?

Thanks for your help!
Corbin

Best Answer

Well, to simplify the maze somewhat, you have all the usual loads of an all-electric house.

  • 50A furnace
  • 50A range
  • 30A air conditioning pack
  • 30A dryer
  • Eleven 120V branch circuits, some MWBC, many on 30A breakers (WTH?)

Obviously we can oversubscribe this somewhat, e.g. You're not likely to run heater and A/C at the same time.

The fine art of panel subscription is not a core skill for me, but hopefully this summary will make it easier for someone else.

That panel, though

While we're here, we gotta talk about that panel. First, panel B top-tapping panel A before the main breaker is very dangerous unless there is another main breaker before this. The meter is not a fuse, and there are no fuses between the transformer and main breaker. This is considered acceptable for a very short hop from the meter to the main, however, in your case this totally unfused feeder crosses your whole house. Nothing prevents a short in the cable, or in this panel, or summed loads on this panel, from setting that cable on fire.

Second, all 4 panels are Federal Pacific "StabLok". It has serious issues with panel fires due to bus defects, and unreliable trip. When feasible, all four should go.

The three subs will be straightforward to DIY, the main will be more troublesome unless there's an outside main breaker. I would DIY install a 200A main service panel right next to it as a subpanel, reuse that 70A breaker to feed it, and move all the 120V circuits out of the main into the new sub. Then bring in an electrician to cut it over to be the new main.

I see many branch circuits on 30A breakers. Those should be 15 or 20 depending on wire gauge.

Gaps in the panel covers should be patched so curious fingers can't touch buses, except finding either breakers or blanks to cover those spots will be a pain.

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