Electrical Wiring in the Home/Water Heater Split


QUESTION: I have a long time tenant that's having trouble sharing the Water Heater Bill with a new tenant...the excuses for not having the money have gotten old.

I replaced the WH 3 years ago when the sharing problem was no problem & don't want to get another one until I get some feedback on an idea I had. Splitting the WH elements isn't fair since they don't both do heating top-offs.

It's an upstairs downstairs rental with a single phase double-drop to 2 Meters & of course separate electrical panels. It's a partial basement that's too tight already, so I can't really fit another WH or 2 small ones. Basically, the basement room was a built-in shed with Stairs, HVAC & Laundry appliances leaving just a 30-inch walkway & Exterior Door under the Stairs.

I don't see any problem with this idea compared to a standard install, but need a 2nd opinion for safety & reliability. It's a 50-gallon tank burning 5000-watts. I can't get my setup on camera, it's that tight down there, so I made & attached a mockup.


Should it not be done for any reason beyond not being conventional?

Should I go to 8-AWG?

Bump up to 20-AMPS into 40-AMPS?

Any problem mounting both neutrals & grounds to the new Subpanel?

Would GFCI or AFCI breakers benefit anywhere or would they nuisance trip?

Is there better wording for the inside panel labeling?

I'm open to anything better & not distressed by a good scolding.


ANSWER: Not a good idea. Imagine that someone turns off the breaker to sub panel A thinking it is dead. But you are back feeding Panel A from Panel B through the water heater sub panel.

To be completely fair, the only thing I can think of (besides of adding another water heater) is to put a flow meter on each apt's hot water line. Then with a little math you can figure out how much each person owes.

A 50 gallon water heater is pretty big. Have you considered mounting two small ones (one above the other) in that space instead of the big water heater? Then you could feed each one from a different panel.

---------- FOLLOW-UP ----------

QUESTION: So, you don't think the Panel Labeling as shown for all 3 would be sufficient instruction? I totally get what you're saying about a person who shouldn't even be using a light switch. I can easily go to childproof panel covers to keep them out eternally.

However, your Back Feed has me very confused. The only place at all, & it's only almost, where the Hot's "meet" is at the WH's internal elements:

Lugs aren't shared, Bus-Bars are entirely separate, Main Panels aren't connected in any way & I don't get Back Feed from any other Double or Single Breakers, not even from a 2-circuit double gang outlet box.

Would 2 Single Breakers bound to trip together in the Subpanel eliminate your Back Feed that would or might commonly occur in a Double Breaker?

And, thanks for the smaller heater stacking idea. That, might become the new Plan B.

ANSWER: I forgot you were talking about wiring one set of elements to one breaker and the other set to another. If they were to be kept separate then there would be no back feeding.

What you are talking about is rewiring the water heater.

Separating the elements is not exactly fair to one, if fair is what you are after.

I love being creative and controlling different devices through the use of relays, xfmrs, etc.

However, I am not real comfortable with rewiring the water heater especially in a rental.

In the long run I think you should go with two smaller ones and be done with it.

---------- FOLLOW-UP ----------

QUESTION: I'm sorry but you misunderstand. I will NOT be re-wiring the WH, because it's not as fair as splitting the supply lines.

There will be no WH labeling nor mention AT ALL in either Panel A or B & the WH will ONLY be labeled on & in the Subpanel (C). This way no-one can logically make any mistake.

But then you said, I'd have a Back Feed problem ONLY IF some monkey wandered in to just flip any switch in Panel A or B, since there would be no labeling nor mention of the WH in either.

Then I asked where the Back Feed would come from since neither supply line is ever connected to each other at any point. If there's no supply there's no Feed in any direction.

Please remember we're talking about Resistance Heating. There's NEVER any supply lines connecting, even if an element fails the supplies only become capped. If 1-side shuts down nothing changes for the other side.

Not to offend but, are you comfortable in understanding this, it's really not anything complicated & only slightly above wiring an outlet.

I only say this because you seem distracted or rushed & hadn't answered any of my other initial questions either. And, why would I have made the circuit mock-up? I'm not confused, I'm entirely comfortable with everything in the mock-up


Should I then assume there's nothing wrong with my design?


Can you pass me off to someone else?


Should I re-post to another Expert?

Let me say this as plain as I can;

I do not condone feeding a water heater from two different sources.

I do not condone rewiring the water heater so one element is fed from one meter and the other element is fed from a different meter.

Your lack of technical understanding leaves me no choice but to abandon trying to explain any thing further.

You are free to "pass" yourself on to someone else.

Good day.
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Greg Hughes


Troubleshooting electrical including appliances and HVAC.


34 years of experience.

Both college and tech schools in this field.

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