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Here’s my situation. I am trying to add an electric tankless hot water to a 4 unit building. 4 separate circuit breaker box present. The water heater requires 4 sets of 40 Amp breakers at 220-240 volts. I will need to add a separate breaker box which I want to use the 4 existing boxes to supply electricity to. I will take it between the meter and breaker box, thereby eliminating the need to go through the existing circuits but still have it registered on the electric meter. And hence, let the hot water usage be shared among the 4 existing boxes.

My issue is, once I connect all 4 existing box to the new one to supply electricity to the water heater box, I will effectively combine all 4 existing meter as one. I NEED to prevent that. So I’m thinking that just before the existing boxes connects to the new one, I can add something to prevent box A from from drawing from box B, C &D. This will allow flow of electricity only in the direction from boxes ABCD to the new box for the water heater. I am not an electrician but I am handy, so any detailed answer will be appreciated. This way I can have help to evaluate whether it’s possible or not and whether I’ll need a skilled electrician to undertake.

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  • Draw a schematic or block diagram. Your block of text will be much easier to follow.
    – winny
    Commented Jan 13, 2018 at 17:29
  • 4
    You're going to burn your house down. Please hire an electrician.
    – Jeroen3
    Commented Jan 13, 2018 at 17:38
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    There are so many things wrong with this, but did you consider that those 4 circuits likely aren't equally used? Likely under low flow conditions they are not. You also are creating a dangerous situation where 4 breaker boxes must be accessed to safely disconnect one piece of equipment--- nothing about your question is safe or sane.
    – Tyson
    Commented Jan 13, 2018 at 18:28
  • winny - yes a diagram would have made this much clearer- Thanks............ Jeroen3 - I was not planning to mess around with 220/240 volts at this amperage. I am at the research state to see if its even possible. Turns out it is not but there are alternate way forward such as a new breaker box with its own meter or separate heating unit... Tyson - lol. I dont think you follow the text properly. A diagram as suggested earlier would have been the better way to provide the details. This post was to answer the question of if its possible to prevent that from happening. But it's not possib
    – S. A.
    Commented Jan 14, 2018 at 22:01
  • If I read this correctly it would not be legal in the U.S. (a water heater fed from 4 sources. It would be safer to feed this from 1 service and split the power usage.
    – Ed Beal
    Commented Jan 14, 2018 at 22:59

2 Answers 2

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Can't be done.

You should get a new meter installed for the water heater.

It's up to you how you get the tenants to pay for the usage. However without also adding hot-water meters for each tenant there is no way to know who is drawing the water and using the power.

Normally landlords embed the common costs in the rent for all units. Or swallow it as cost of doing business.

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    Thanks. This is what someone from Home Depot suggested as well. To add a separate meter or use 4 separate hot water tank.
    – S. A.
    Commented Jan 14, 2018 at 21:54
  • @S.A. having the heater on a separate feed is probably a good idea anyway. The inrush current on those things is nasty and can cause the lights to dim, electronics to act up.
    – Trevor_G
    Commented Jan 14, 2018 at 22:01
  • @Trevor_G Water heaters do not have inrush, because resistors don't have inrush. If you get a voltage sag when it kicks on, that's your wiring; or you have a tanked heat pump type with a compressor motor.
    – Harper - Reinstate Monica
    Commented Jan 14, 2018 at 22:44
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I get what you're trying to do, but you absolutely cannot do that thing that way. This is serious paralleling, and will cause havoc with imbalances of load - especially when tenants discover they can shut off a certain breaker in their box, and poach electric power from their neighbors for free. Don't be surprised if one of them gets in the Bitcoin mining business.

You will also have big tenant problems when they find out each of them is paying for everyone else's hot water usage. They won't see it as equal, they will feel others use much more than themselves. So even if it was possible to electrically isolate the four heating-coil sections and serve each from a separate service, this entire concept is trouble.

In fact it sounds like you don't really care who pays for the power this thing uses, as long as it isn't you. I'm not sure why; it will use less energy than your previous heater, and be a net savings.

Not surprisingly, there is landlord-tenant law to cover this exact situation. Your AHJ would never issue a permit for the type of splitting you want to do (and if you're doing this without a permit, that's super dumb and you will get nailed hard when caught).

If you meter tenants separately, you must also have an extra meter for commons loads - such as commons hallway lighting and heat, security lighting, yard bug zappers, garage door openers, coin washer-dryers, and yes: water heaters if shared. This is a requirement of building and electrical codes. But even then, you can't force tenants to split the actual commons-load bill, you must flat-rate that (by building it into the cost of rent). Yes, that does create a perverse incentive: if they waste hot water, you pay, not them. That is the trouble with commons hot water.

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  • That was the reason for asking about "something" that prevents the electricity from flowing from one box to another. But as I found out, it cannot be done. Adding a separate meter is the way forward. It's part of their lease agreement to cover their own hot water cost but I am not researching how to go about doing this without having to re-plumb the whole house. Either a new meter or 4 separate hot water system. At any which rate, dividing up the cost will never be accurate since usage varies and would ultimately have to be covered by the landlord. Thanks for the clear and concise response.
    – S. A.
    Commented Jan 14, 2018 at 21:55
  • A lease agreement can't override state law. You might want to get some books like "The landlord's Law Book" or "Tenant's Rights" both by Nolo.The only legal way I can see to make them pay hot water is give each unit its own heater punched down on its own electric service.
    – Harper - Reinstate Monica
    Commented Jan 14, 2018 at 22:32
  • I think he could add a meter on each supply and divide the cost by the % of the total usage. I believe this is the way a friend is doing it , I wired the water meters & some power monitors a few years back.
    – Ed Beal
    Commented Jan 14, 2018 at 23:07
  • Ed Beal ---Yes, adding a separate meter was suggested. Then dividing up the cost using a specified matrix that must be on the lease. However, I do not know if there are any statues that impose rules on this other than landlord can only bill for actual cost but I am getting mix info on what is considered actual cost... Harper..which of those 2 books are more comprehensive for FL? That is, include both landlord's rights/duties and that of the tenants as well. I had seen one with case examples in the law library but didn't take down the ISBN or title. I think it's a worthwhile investment for me.
    – S. A.
    Commented Jan 15, 2018 at 3:04
  • @S.A. "The Landlord's Law Book" is certainly more inclusive, as it was 2 volumes in the 90s, maybe more now. But "Tenant's Rights" is a good complement as it will get you thinking like a tenant, which is an sensibility you could definitely use more of. Notice here, how you made a beeline for the most unworkable (from the tenant's POV) option, without even realizing you did. Nobody in my complex would put up with that.
    – Harper - Reinstate Monica
    Commented Jan 15, 2018 at 15:24

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